Department of Chemistry and Chemical Biology

 

 

Ch-362

Fall 2005

Instrument Analysis I, Laboratory Manual

Room 429 McLean Building

Section C: Monday 12:00 -3:50 PM

Section A: Tuesday 02:00 -5:50 PM

Section B: Friday 02:00 -5:50 PM

Professor Athula Attygalle

312 McLean Building

216-5575

aattygal@stevens-tech.edu

http://www.chem.stevens.edu/MassSpectrometry/

Office hours:

Tuesdays 1:00 – 2:00 PM

   
   
Teaching Assistants  
 

Constantine (Dean) George (cgeorge@stevens.edu)

 

 

Office hours:

0.5 hr after each lab

Hyeunjoo Lee (hyeunjoo2@yahoo.com)

hlee6@stevens.edu

 

Office hours:

0.5 hr before each lab

 

 

 

 

Safety Rules

The following regulations are an absolute necessity for a safe laboratory. Please read them carefully, as signing the slip below indicates your agreement to abide by these rules. Since there are hazard risks associated with non-compliance (fire, explosions, burns, etc.), you may be asked to leave if you don’t follow these rules.

1. Safety goggles must be worn at all times in the laboratory (TAs have been instructed to subtract 10 points for each failure). Wear a lab coat or an apron to protect your clothing.

2. Report any accidents and injuries immediately to your instructor.

3. No eating or drinking in the laboratory. Do not taste or smell chemicals, unless you are instructed to do so.

4. Do not sit on bench tops.

5. Clothing must be appropriate for the lab; no shorts, short skirts, sandals, tank tops, or high heels.

6. Long hair must be tied back. It is advisable to minimize the use of hair sprays and other hair products, because they are highly flammable.

7. Contact lenses should never be worn in the laboratory.

8. Be aware of the location of the safety shower, eyewash station, fire extinguisher, first aid equipment, and the exits.

9. All experiments must be approved by the instructor. Do not perform un assigned or unlisted experiments

10. Know the hazardous properties of the chemicals you are using. Specific instructions for dealing with hazardous material will be given by the instructor prior to their use. Read MSDS (Material Safety Data Sheets) information. When in doubt, ask! Use gloves appropriately. Note that if you use gloves to handle hazardous chemicals, your gloves are contaminated. Do not handle clean equipment with contaminated gloves. Do not operate computer and instrument keyboards with contaminated gloves. To carry a chemical bottle use only one hand with a glove on. Use the other hand without a glove to do other tasks such as opening doors. Remove gloves when writing notes.

• Use the fume hoods when instructed.

• Dispose of hazardous waste as instructed. No chemical should be poured to municipal drains.

• Do not pipet by mouth.

11. Use only the chemicals called for in your experiment. Make sure you know what chemicals you are looking for. Many chemicals have similar names or formulas. Treat all chemicals as hazardous.

12. All substances must be properly labeled.

13. No chemicals, supplies, or equipment may leave the laboratory.

14. You may not work alone in a lab.

15. Follow your instructor’s procedure when pushing glass tubing through corks and rubber stoppers.

16. Wash your hands before leaving lab.

Other Rules

Keep the laboratory floor, benches and walls clean (do not put your feet on walls and leave shoeprints). Before leaving the laboratory, clean your work area and wipe it dry.

Users of the Electronic Balance. If you find the balance dirty, you can refuse to use it (and go home). On the other hand, if you must use it (because you have to finish an experiment before a deadline), you must clean the balance yourself. The excuse that someone else is responsible for the dirt is never acceptable in a scientific laboratory. If you spill chemicals or other material in the balance itself, or on the bench, you must immediately sweep out the contaminant with a brush before proceeding.

No "walkmans" and other music devices, no earphones, no cellular phones with audible ringing tones.

Instrument computers should not be used for any other purpose (no web-browsing, down-loading. games, or music; no exceptions to this rule)

Please sign and return this slip to your instructor.

I have read and understand the chemical laboratory safety rules and regulations, and agree to abide by them.

Safety Rules

The following regulations are an absolute necessity for a safe laboratory. Please read them carefully, as signing the slip below indicates your agreement to abide by these rules. Since there are hazard risks associated with non-compliance (fire, explosions, burns, etc.), you may be asked to leave if you don’t follow these rules.

1. Safety goggles must be worn at all times in the laboratory (TAs have been instructed to subtract 10 points for each failure). Wear a lab coat or an apron to protect your clothing.

2. Report any accidents and injuries immediately to your instructor.

3. No eating or drinking in the laboratory. Do not taste or smell chemicals, unless you are instructed to do so.

4. Do not sit on bench tops.

5. Clothing must be appropriate for the lab; no shorts, short skirts, sandals, tank tops, or high heels.

6. Long hair must be tied back. It is advisable to minimize the use of hair sprays and other hair products, because they are highly flammable.

7. Contact lenses should never be worn in the laboratory.

8. Be aware of the location of the safety shower, eyewash station, fire extinguisher, first aid equipment, and the exits.

9. All experiments must be approved by the instructor. Do not perform un assigned or unlisted experiments

10. Know the hazardous properties of the chemicals you are using. Specific instructions for dealing with hazardous material will be given by the instructor prior to their use. Read MSDS (Material Safety Data Sheets) information. When in doubt, ask! Use gloves appropriately. Note that if you use gloves to handle hazardous chemicals, your gloves are contaminated. Do not handle clean equipment with contaminated gloves. Do not operate computer and instrument keyboards with contaminated gloves. To carry a chemical bottle use only one hand with a glove on. Use the other hand without a glove to do other tasks such as opening doors. Remove gloves when writing notes.

• Use the fume hoods when instructed.

• Dispose of hazardous waste as instructed. No chemical should be poured to municipal drains.

• Do not pipet by mouth.

11. Use only the chemicals called for in your experiment. Make sure you know what chemicals you are looking for. Many chemicals have similar names or formulas. Treat all chemicals as hazardous.

12. All substances must be properly labeled.

13. No chemicals, supplies, or equipment may leave the laboratory.

14. You may not work alone in a lab.

15. Follow your instructor’s procedure when pushing glass tubing through corks and rubber stoppers.

16. Wash your hands before leaving lab.

Other Rules

Keep the laboratory floor, benches and walls clean (do not put your feet on walls and leave shoeprints). Before leaving the laboratory, clean your work area and wipe it dry.

Users of the Electronic Balance. If you find the balance dirty, you can refuse to use it (and go home). On the other hand, if you must use it (because you have to finish an experiment before a deadline), you must clean the balance yourself. The excuse that someone else is responsible for the dirt is never acceptable in a scientific laboratory. If you spill chemicals or other material in the balance itself, or on the bench, you must immediately sweep out the contaminant with a brush before proceeding.

No "walkmans" and other music devices, no earphones, no cellular phones with audible ringing tones.

Instrument computers should not be used for any other purpose (no web-browsing, down-loading. games, or music; no exceptions to this rule)

Please sign and return this slip to your instructor.

I have read and understand the chemical laboratory safety rules and regulations, and agree to abide by them.

_______________________________ ___________

Signature Date

__Ch-362/561________________________

You must know where to find MSDS (Material Safety Data Sheets) information for each chemical you use.

(http://www.ilpi.com/msds/)

Hazardous Material Classification

NFPA (National Fire Protection Association) hazard identification coding system

Fire Hazard Identification System

Fire Hazard - Flash Points

4 - Below 73 F

3 - Below 100 F

2 - Below 200 F

1 - Above 200 F

0 - Will not burn

Health Hazard

4 - Deadly

3 - Extreme danger

2 - Hazardous

1 - Slightly hazardous

0 - Normal material

Reactivity

4 - May detonate

3 - Shock and heat may detonate

2 - Violent Chemical change

1 - Unstable if heated

0 - Stable

Specific Hazard

Oxidizer - OXY

Acid - ACID

Alkali - ALK

Corrosive - COR

no water -  

Radiation Hazard - 

 

 

Ch-362 consists of laboratory sessions and lectures. Fifty percent of your final grading will be based on laboratory work, which consists of seven units.

 

Grading (per unit)

  Points
Pre-lab Report submitted on time (a week before the experiment). 2
Pre-lab Report contents 8
TA evaluation 5
Final lab report (due a week after the experiment) 35
No Excel sheet Minus 10
Late submission (two weeks after the experiment).

Reports will not be accepted 2 weeks after the due date (Reports may be computer-assisted, typed or hand-written. Excuses such as "my computer crashed, my printer ran out of ink, my partner had all my data, etc" are not acceptable, since hand-written or typed lab reports are acceptable. Reports on compact disks or diskettes are not acceptable. Electronic submissions require prior approval from the TA.

Minus 10
Total per unit 50

Final Grading for Lab Work

 

Seven Units ( 50 x 7) 350
Proper use of pipettes, burettes, and electronic balances) 80
Lab Notebook (submit all lab notebooks to your TA on or before December 9 , 2005) 35
TA Evaluations 35
Total 500

Last day for you final lab report is December 9, 2005.

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Pre-Lab Reports

Preliminary Lab Reports: The mission of this course is to develop good analytical thinking and problem solving capabilities in students. Students are required to plan their work prior to their arrival in lab. Many calculations that are necessary for the experiment must be done before coming to the lab session. If you have to do these calculations after coming to the lab, you will not have enough time to finish experimental procedures. Each student is required to write a preliminary lab report for each unit. A prelab reoprt is worth 10 points and is due a week before the beginning of the lab period. TAs will not allow you to proceed with any experiment without a pre-lab report. Two points are awarded if it is turned in on time, zero if it is late. The other 8 points depend on the quality of your report, as discussed below.

The preliminary reports should include the following four sections. Where appropriate, write complete sentences and use proper grammar. Please number your responses (1 - 5)

1) Title of the Experiment, Date of Experiment

2) Name of Technique:

1. Present a schematic (block) diagram of the instrumental technique that shows its essential components.

2. Write in your own words a brief summary describing how the technique works. If you cut and paste from Web pages give proper acknowledgement and make sure you understand the content. You will be penalized if you cut and paste material that you don’t understand.

3) Use of the Technique for your Experiment:

a) What types of samples can be analyzed by this technique? In other words, what physical or chemical properties must samples have in order to be determined by this technique?

b) What physical or chemical property of the sample is probed in this measurement?

c) How can the technique be used for qualitative and/or qualitative measurements?

d) What the major advantages and limitations of the technique?

e) Describe the nature of the signal. (What is actually being detected?)

Calculations:

a) Calculate (tabulate if necessary) the molecular weights needed for your estimations.

b) Give the amounts that will be weighed (tabulate, if necessary), in what volumes they will be dissolved. Show how dilutions will be made if that is required (tabulate if necessary).

5) References: Include complete citations showing title, author, publisher, year, etc. You must use at least two sources. Follow the format used by the journal "Analytical Chemistry." Here are examples of the reference format:

(1) Koile, R. C.; Johnson, D. C. Anal. Chem. 1979, 51, 741-744.

(2) Willard, H. H.; Merritt, L. L., Jr.; Dean, J. A.; Settle, F. A.,

Jr. Instrumental Methods of Analysis, 6th ed.; Van Nostrand:

New York, 1981; Chapter 2.

If you cut and paste Figures from the WWW, the URL of the reference must be given. Direct cut and paste of text from the internet will get you a poor grade. Explain in your own words, what is required.

MSDS Safety Issues and Chemical Hazard Information

6) Provide answers to any prelab questions asked in the instructions sheet?

 

 

 

 

Laboratory Notebook

Students must maintain a hardcopy laboratory notebook. Data should be entered in such a way that any other analyst is able to follow you techniques and results, or reproduce the results if necessary. Neatness and reliability is an integral part of good laboratory practice.

On the title page of laboratory note book write your name, address, telephone number, email address, name of the course and instructor’s name.

The first 3-4 pages should be reserved for the Table of Contents.

Data must be recorded Immediately in the note book with a pen (no pencils) (the excuse, I lost all my data due to a computer crash is not acceptable).

Each experiment should have a title, and the start date.

Data must never be recorded on loose sheets of paper.

If you make an error, neatly draw a single diagonal line thought the entry, and use a fresh page. Use of Tipp-Ex, ink bleaches and eradicators, and erasures are not allowed.

Pages must never be removed from the note book.

The note book should be available for inspection at any time.

After recording data and before leaving the lab, students must obtain the signature of the TA on the page they have recorded data. Submit all lab notebooks to your TA on or before December 9, 2005. You receive 25 points for properly maintaining your lab note book.

===============================================================

Computer: Bring your laptop with Excel to each lab session. Do you calculations before you leave the lab and show them to your TA.

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Final Lab Report:

After finishing each Unit, a laboratory report must be submitted within a week. Each report is worth 35 points.

The final lab reports must be typed using a word processing program. When you work with a partner you will share data, however, each person must write an independent lab report. The final report should be your own writing. Laboratory reports are also exercises in learning how to communicate in a formal manner. Utmost attention to detail is required. Imagine you are writing a scientific paper. Follow the style of the journal "Analytical Chemistry." (Check http://pubs.acs.org.)

TITLE: The title should accurately, clearly, and concisely reflect the emphasis and content of the paper. The title must be brief and grammatically correct. Copying the title from the instruction sheet is not acceptable.

Bad Tile: "Gas Chromatography"

Good title: "Quantitative Determination of Caffeine in VegiCola by Gas Chromatography"

AUTHOR NAME: (Include names of all members of the group. Use first names, initials, and surnames (e.g., John R. Smith).

AUTHOR ADDRESS: The affiliation should be the institution where the work was conducted.

ABSTRACT: All reports must be accompanied by an abstract (one paragraph). The abstract should briefly state the problem or purpose of the experiment, indicate the theoretical or experimental plan used, summarize the principal findings (include numerical values you found), and point out major conclusions. Experimental and instrumental details are not required in the abstract.

INTRODUCTION: One or two paragraphs. Do not describe the whole technique (this should in the prelab report), but describe the important points of the experiment.

Experimental Section

Describe the procedures undertaken. Follow the style of the journal "Analytical Chemistry."

RESULTS AND DISCUSSION

Present calculations, figures, tables here.

FIGURES AND CAPTIONS. Each figure must have a caption that includes the figure number and a brief description, preferably one or two sentences. The caption should immediately follow the figure with the format "Figure X. Figure caption.". All figures must be mentioned in the text consecutively and numbered with Arabic numerals. The caption should be understandable without reference to the text. Place the keys to symbols used in the figure in the caption, not in the artwork.

TABLES. Each table must have a brief (one phrase or sentence) title that describes its contents. The title should follow the format "Table X. Table Title" . The title should be understandable without reference to the text. Put details in footnotes, not in the title. Define nonstandard abbreviations in footnotes.

Use tables when the data cannot be presented clearly as narrative, when many precise numbers must be presented, or when more meaningful interrelationships can be conveyed by the tabular format. Tables should supplement, not duplicate, text and figures. Tables should be simple and concise. It is preferable to use the Table Tool in your word-processing package, placing one entry per cell, to generate tables.

REFERENCES. Place references at the end of the report. In any case, place your list of references at the end of the manuscript.

Read recommendations given in The ACS Style Guide, 2nd ed., available from Oxford Press. Always use complete sentences, coherent statements, and consistent tense throughout the report. Although most word processing programs will discourage you, use the third person passive tense in your writing. That is the style for scientific reporting.

Do not use first person tenses: "I weighed out 10.0 g of bubliomatric acid."

Do not use second person tense: "You weigh out 10.0 g oxalic acid."

Also do not write instructions in the imperative tense: "Weigh out 10.0 g NaCl."

Instead, use the third person passive tense: "10.0 mL of NaOH solution was measured." ("not were measured")

In regular writing, third person passive is considered weak, since action is performed to an object instead of that object actually doing the action. However, for scientific writing, this tense is perfectly acceptable since it is understood that the lab has already been done (past tense action) and the reader knows who did the lab (your name was on the paper).

Hints

Acceptable Not acceptable  
0.05 g .5g (note the zeros and blank spaces)
0.1 M solution 0.1 Molar solution  
50 0C 500C space
254 nm 254nm space
A = 5 A=5 note spacing
25- to 30-mg samples    
Five grams of NaCl was added to the solution. Five grams of NaCl were added to the solution. grammar
None of the samples were soluble. None of the samples was soluble. grammar

Proper use of pipets, burets, and electronic balances. Gloves. Dilution.

Proper Pipeting Technique for Fixed Volume Pipets

 

1. Clean pipet thoroughly and rinse with deionized water.

2. Drain completely, leaving no rinse-water drops inside. If the pipet is wet with rinse water, rinse three times with a few milliliters of the solution to be used in the analysis. DO NOT SUCK SOLUTION MY MOUTH.

3. Keep the tip of the pipet below the surface of the solution.

4. Draw the liquid up in the pipet using the pipet bulb. Never use your mouth.

5. Disconnect the suction device when the liquid is above the calibration mark. Quickly remove the suction device and immediately place the index finger (not the thumb) of the hand holding the pipet over the exposed end of the pipet to close the end. Do not hold pipet by the pipet bulb (why?).

6. Remove the pipette tip from the solution, and then wipe any excess fluid from the exterior of the tip with a lint free tissue being careful not to touch the bottom of the tip.

7. Hold the pipet vertically, and let the pipet tip touch the inner wall of the volumetric flask, or any other container holding the solution being measured. Release pressure on the index finger to allow the meniscus to approach the calibration mark. You must practice this until you are comfortable with this technique.

8. At the mark, apply pressure to stop the liquid flow, and drain the drop on the tip by touching it to the wall of the container.

9. Wipe the outside of the pipet with a tissue to remove any droplets adhering to the outside walls. (Do not to touch the bottom of the tip).

10. Transfer the pipet to the receiving container. Hold the pipet vertically and touch with the pipet tip the inner wall of the receiving tube (you may tilt the receiving container appropriately) and release pressure on the index finger. Allow the solution to drain completely. Wait 10 seconds (Count up to ten) to allow complete dispensing of the sample solution. Note that the liquid is allowed to drain out and NOT forced out Therefore, DO NOT remove by blowing the little amount of liquid that remains at the pipet tip.

Final lab Report, Check list, and Grading codes

A) No abstract (-5 points)

B) Wrong numerical results, or no results (-5 points)

C) No final (numerical) results given in the abstract (-2 points)

D) Introduction too short, or insufficient description of the technique (-2 points).

E) Experimental. Instrumental names and sources of chemical are not given (-1 point). Incomplete sentences (-1 point). Sentences not in past passive voice (-1 point).

F) Dilutions are not described in detail (-2 points).

G) Figures cut and pasted from external sources without giving proper credit (-2 points).

H) No Excel sheet (-5 points)

I) No cell and row numbers (-1 point)

J) No cell formulas (-2 points).

K) Wrong cell formulas (-1 point)

L) No Figures and Tables within the Results and Discussion section (-2 points). (Statements such as, "Please see attached sheets" are not acceptable)

M) No axes labels in Figures (-1 point for each occurrence)

N) No Figure or Table caption (-1 point).

O) Improper selection of axes scales (-1 point).

P) No units (-1 point for each occurrence)

Q) Wrong number of significant figures (-1 point).

R) Poor experimental results (-4 points).

 

 

 

Unit 0: Volumetric Redox Titration

Unit 1: ATOMIC ABSORPTION SPECTROMETRY

UNIT 2: Ultraviolet-Visible Spectroscopy

Unit 3: Fourier Transform-Infrared Spectroscopy

Unit 4: Gas Chromatography

Unit 5: Solid phase micro-extraction (SPME)

Unit 6: High Pressure Liquid Chromatography

Unit 7: Spectrofluorometry

Unit 8: Polarimetry

 

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Unit 0: Volumetric Redox Titration

This is a practice unit. You will submit pre-lab and final reports. They will be corrected, graded, and returned to you. This is a mock grade. Study your evaluation report and discuss with your TA and the professor how to improve your grade

Introduction

Many redox titrations are based on reactions of iodine. An oxidizing agent is added to excess iodide to produce iodine, which is then titrated with sodium thiosulfate, the reducing agent.

Iodine

iodide triiodide

In this experiment, potassium iodate (KIO3) is used as a primary standard (what is a primary standard?). From a known amount KIO3, an equivalent amount of triiodide (iodine dissolves in iodide solutions to form triiodide) can be formed.

...(1) (reduction)
.(2) (oxidation)
…..(3) (multiply 1 by three)
…..(4) (add 1 and 3)

Since I2 exits as triiodide in the presence of excess iodide, eliminate iodine from equation 4.

...….(5)
……(6) (multiply 5 by three )
…..(7) (add 6 and 4)

Sodium thiosulfate is a universal titrant for triiodite, which oxidizes it to tetrathionate.

…..(9) (oxidation)
…..(10) (reduction)
 

..(11)(add 9 and 10)

As thiosulfate solution is added, the dark brown color of I3- solution disappears. Near the end point (pale straw color), a starch solution is added and titrated until the Prussian blue color of the starch-iodide complex disappears.

The main objective of this experiment is to use the two solutions you have to estimate the amount of ascorbic acid (vitamin C) present in a commercial tablet. This can be done iodimetrically since vitamin C is a mild reducing agent. The idea is to let ascorbic acid from a tablet react with a known excess amount of I3-, and then find out the amount left, by titrating with the standard thiosulfate solution. In this way, the amount of ascorbic acid in a tablet can be computed.

 

H2O

 

 

+2H+ + 2e

 

 

…(12)

Ascorbic acid

 

Dehydroascorbic acid

   

Equipment

Erlenmeyer flasks

Volumetric flasks (250.00 mL)

Buret (50 mL)

Pipet (50.00 mL)

Pipet filler

Reagents:

Na2S2O3 solution (supplied by the lab instructor; approximate molarity provided; you must determine the exact molarity)

KIO3 (solid, note the name of the supplier)

Starch solution

Solid KI

0.5 M H2SO4 solution

Vitamin C tablets.

 

 

Procedure

Prepare 250 mL of approximately 0.01 M standard KIO3 solution (you must calculate the amount to weigh and report in the prelab report).

Pipet 50.00 mL of the KIO3 solution you prepared to an Erlenmeyer flask (this is a quantitative transfer), and add approximately 2 g of solid KI and 10 mL of 0.5 M H2SO4.

Rinse first, and then fill a 50 mL buret with the Na2S2O3 solution provided.

Immediately titrate with thiosulfate solution until the solution is pale yellow.

Add about 1 mL of starch indicator (why starch?), and titrate carefully until the blue color disappears.

Repeat the titration with two additional 50.00-mL portions of KIO3 solution.

Break a vitamin C tablet to two halves. Crush one half, and measure the weight accurately (about 250 mg).

Transfer the powder quantitatively to an Erlenmeyer flask and dissolve the material in 50 mL of 0.5 M H2SO4 in (note: some solid biding material may not dissolve).

Add 2 g of solid KI and 50.00 mL of standard KIO3 solution. Titrate with standard thiosulfate solution as before. Add starch solution just before the end point.

Calculations

(1) Calculate the molarity of the KIO3 solution.

(2) Calculate the molarity of the Na2S2O3solution.

(3) Calculate the weight percentage of ascorbic acid present per tablet.

 

 

 

 

Unit 1: ATOMIC ABSORPTION SPECTROMETRY

Unit 1: EXPERIMENT I: Determination of Copper by Ordinary Linear Calibration Method

Introduction

Atomic Absorption Spectrometry (AAS) is based upon absorption of radiation by free atoms. Almost any solid, liquid, gaseous sample can be analyzed by AAS. However, it is more convenient to convert samples to homogenous solutions prior to use.

Usually, a solution is aspirated into a hot flame of about 2000-3000 K. In the flame, solvent evaporates and remaining solid is broken into atoms. By providing from a radiation source, a selected wavelength specific to the element being determined, transition of electrons from the ground state to an excited state can be achieved. By measuring the amount of radiation absorbed, a quantitative estimation of the amount of analyte can be accomplished.

Basic Instrument Design

The components in an atomic absorption spectrophotometer are:

A light source.

A high temperature flame such as air-acetylene into which a sample solution is aspirated.

A monochromator

Theory

The concentration of a metal ion in a sample solution can be determined by constructing a calibration plot. This technique is known as Ordinary Linear Calibration. To construct such calibration graph, a series of calibration standards are prepared. These calibration standards should be prepared in the same solvent as the unknown sample so that the flow rate of the sample and the standards are identical.

A plot of absorbance vs. the concentration of the ion in each solution, according to Beer's law, is a straight line. From this calibration graph, the concentration of the unknown is found by interpolation.

Equipment

* 1-L volumetric flasks (1)

* 100-mL volumetric flasks (4)

* 100-mL beakers (5)

* 10-mL graduated cylinder (1)

* 1-mL volumetric pipet (1)

* 2-mL volumetric pipet (1)

 

Reagents

* 1.60 x 10-3 M CuSO4 (formula weight of CuSO4.5H2O 249.68), 1000-mL (0.400 grams per liter).

* Unknown, distilled, and deionized water samples (supplied by the laboratory instructor.)

Procedure

(1) Clean all glassware before starting the experiment.

(3) Pipet (volumetrically) 1.0, 2.0, 3.0, and 4.0 mL from CuSO4 stock solution, and place them into four separate 100-mL volumetric flasks. Diluting to the mark with distilled water will yield concentrations of 1, 2, 3, and 4 mg/mL in copper respectively (you must check and verify whether these numbers are correct).

(3) Turn on the atomic absorption spectrophotometer according to instrument's operating manual.

(4) Measure the aspiration rate by placing 10-mL of water into a graduated cylinder. Then, place the aspirator tube into the cylinder and measure the time. (Adjust the rate to be between 7 to 10 mL/min, if necessary).

(5) Transfer the calibration solutions to four separate 100-mL beakers.

(6) Place some water into a 100-mL beaker, and aspirate for approximately 15 seconds, then adjust the instrument to read zero absorbance by pressing the Auto Zero key. Aspirate the first solution into the flame for approximately 15 seconds, and record its absorbance. Repeat step 6 for the remaining solutions.

(7) Obtain four samples of tap water, and deionized water and record their absorbances. Record the absorbance of an unknown sample (four times) supplied by the laboratory instructor. If the concentration is outside of the calibration range, make an appropriate dilution. Use an Excel Data Sheet to record the raw data (Note: Do not discard the unknown sample. You will need this sample for Experiment II.)

Calculations

 

(1) Construct a linear calibration graph by plotting absorbance vs. concentration (mg/mL) of Cu in solution (Use Excel).

(2) Determine the concentration of Cu in tap water, deionized water and unknown sample.

 

Unit 1: Experiment 2: Analysis of Copper by the Standard Addition Method

Theory

In standard addition technique, known quantities of analyte are added to a sample of unknown the concentration. From the increase in signal strength, it is possible to deduce how much analyte was present in the original unknown. A calibration graph is constructed and by extrapolating the calibration line, as shown below, to X axis, the concentration of unknown can be determined. Mathematically this relationship can be shown as follows:

Let Ao = Absorbance of unknown when zero amount of known added

A = Total absorbance

a = Absorptivity

b = Path length of light

Cx = Concentration of unknown that we want to determine

Cs = Concentration of standard

Then the following relationship holds true: Ao= abCx ……………(1)

A = ab(Cx + Cs)

A = abCx + abCs …….(2)

Substitute equation (1) into (2): A = Ao + abCs ………(3)

When total absorption (A) is zero then: 0 = Ao + abCs

-abCx = abCs

-Cx = Cs

Equipment

100-mL volumetric flasks (4)

100-mL beakers (5)

10-mL graduated cylinder (1)

1-mL volumetric pipet (1)

2-mL volumetric pipet (1)

Reagents

0.001603 M CuSO4, 1000-mL (0.400 grams per liter)

Unknown sample (supplied by the lab instructor.)

 

 

Procedure

(1) Use the value of the unknown concentration that was found in Experiment I to determine how many milliliters of unknown solution (used in Experiment I) are required to prepare a 100-mL solution that contains approximately 1 mg/mL of Cu; a concentration that falls inside the linear calibration range.

(2) Pipet equal amounts of unknown solution needed to yield approximately 1 mg/mL of Cu into four separate 100-mL volumetric flasks.

(3) Pipet 0, 1, 2, and 3-mL aliquots of stock solution (100 mg/mL in Cu) into the volumetric flasks, and dilute them to 100-mL mark with distilled water.

(4) Follow steps 3 through 6 of Part I, and use an Excel Data Sheet to record the raw data.

Calculations

(1) Construct a plot of the absorbances as a function of the concentration of standard added using Excel. (Be sure to adjust the copper concentration scale to show the intersection of the calibration line at zero absorbance.)

(2) Determine the concentration of copper in the unknown sample. Remember to correct the determined concentration and standard deviation for the dilution.

(3) In your report, discuss the advantage of this method to Ordinary Linear Calibration Method. What are the disadvantages?

=============================================================

Unit 1: EXPERIMENT 3: Determination of Percentage Copper in an Alloy by Ordinary Linear Calibration Method

Reagents

Concentrated HNO3 (diluted 1:1)

Concentrated HCl (diluted 1:1)

Cu(NO3)2.3H2O

Copper coins

Procedure

(1) Dissolve 0.038 g of Cu(NO3)2.3H2O (formula weight 241.60) in 100 mL of deionized water [100 ppm stock solution of copper].

(2) Prepare 4 standard solutions (50 mL each) by diluting the stock solution.

  Concentration of copper Volume of stock solution (mL) Volume of water (mL)
1 8 ppm 4.0  
2 10 ppm    
3 12 ppm    
4 20 ppm    

(3) Clean and weigh accurately a copper coin (note the year it was manufactured). Dissolve the coin completely in 10 mL of HCl and minimum of HNO3 (about 15 mL) (These acids are very corrosive. All operations should be carried out in the hood. Gloves and proper safety goggles are mandatory!). Using a hot plate, bring the mixture to boil to remove oxides of nitrogen. Reduce the heat the moment rigorous reaction starts. One the coin is completely dissolved, cool, and transfer the contents quantitatively to a 100 mL volumetric flask and make it up to the mark with deionized water. Take 2 mL of this solution and dilute to 100 mL quantitatively with deionized water.

Using the AA spectrophotometer record absorbances to plot a calibration curve, and then record the value for the coin solution.

Calculations

Calculate the percentage of copper in the coin. Comment and discuss your results.

Discussion

Discuss the chemical reaction between copper and nitric acid. Write a balanced equation. The brown vapor represents what oxide of nitrogen. Discuss the significance of noting the year of manufacture of the coin.

http://www.usmint.gov/about_the_mint/fun_facts/index.cfm?action=fun_facts2

Unit 1 Final Report. Submit the final report within one week after completion of the experiments. Follow the style of the Journal Analytical Chemistry. Each report must have a comprehensive title, an abstract, a short introduction (material given as the prelab report is not appropriate here), an experimental section, results, a discussion, and a list of references.

UNIT 2: Ultraviolet-Visible Spectroscopy

 

 

l = pathlength (centimeters)

C = concentration (molar, M)

E = molar absorptivity (M-1 cm-1)

 

In absorption spectrometry, we measure the intensity of the fraction of light (radiation) of a selected wavelength that passes through a sample. Most light sources produce a whole range of wavelengths. Passing light first through, a filter or special device called a monochromator enables us to select the appropriate wavelength required for the assay.

In practice, two measurements of the intensity of light are made. First, the intensity of light of the selected wavelength (l) reaching the detector when a sample cell (a.k.a cuvette) filled with solvent (blank) is measured (I0). In other words, represents when the concentration of the assayed material is zero. Then the absorption by the sample is recorded (I). Molar absorptivity (which used to be called the extinction coefficient) gives us an indication how good a compound absorbs light at a particular wavelength. It is numerically equal to the absorbance recorded by placing a molar solution in a cell of 1 cm pathlength.

Prelab Question: What are the units of Absorbance and molar absorptivity?

Unit 2: EXPERIMENT 1. Determination of ascorbic acid in Vitamin C tablets.

Limeys
The True Story of One Man's War against Ignorance, the Establishment and the Deadly Scurvy
David I. Harvie
Review by Patricia K. Crimmin
2002 ISBN: 0-7509-2772-0
L-Ascorbic acid is an important vitamin. Lack of ascorbic acid in diet causes scurvy, a disease characterized by weakness, small hemorrhages throughout the body that cause gums and skin to bleed, and loosening of the teeth. Scurvy was a serous problem for English sailors in the 1600s and 1700s. James Lind, a British doctor, discovered that sailors would not develop scurvy if they were given limes and other citrus fruits. Since this discovery, the Royal Navy made sure that all sailors had lemon juice to drink when they were at sea for longer than one month.

Many believe that ascorbic acid stimulates immune function and protects people from colds and flu-like symptoms. Vitamin C is a water soluble antioxidant, and plays a vital role in protecting the body. Pollutants such as smog and cigarette smoke contain oxidizing molecules that cause tissue damage. Animals make oxidizing molecules in response to infections. Unfortunately, these molecules while killing infecting organisms and cause tissue damage too. The body requires extra vitamin C when fending infections. Since ascorbic acid is a water-soluble vitamin, risk of getting an over dose is minimal and any unused vitamin C will be excreted. The minimum daily requirement is 30 mg, and the recommended daily allowance is 60-70 mg per person.

 

Check this site: http://askabiologist.asu.edu/research/scurvy/

 

Equipment

1) 25 mL volumetric flasks (8)

2) 100 mL volumetric flasks (2)

3) 1 mL, 2 mL, 3 mL, and 4 mL volumetric pipets (one of each)

4) Matching quartz cuvettes (2) (why quartz?)

Reagents

* Reagent grade ascorbic acid (vitamin C)

* Vitamin C tablets

* Absolute ethanol

Procedure

Clean all glassware before starting the experiment.

Prepare a stock solution by weighing accurately about 0.01 g of ascorbic acid, and transfer it into a 100 mL volumetric flask. Dilute with absolute alcohol to the mark. Stopper the flasks, and make sure the solutions are well mixed by turning the flasks upside down.

Pipet 1.0, 2.0, 3.0, 4.0 mL aliquots of ascorbic acid stock solution into four separate 25 mL volumetric flasks (label your flasks, No.1 to 4), and dilute with absolute alcohol to the mark.

Fill two quartz cells (prelab question: why quartz?) with ethanol, set the wavelength range of the spectrometer from 320 to 220 nm, and take a blank spectrum (use the auto-zero procedure)

Obtain absorption spectra from 320 to 220 nm of all four solutions of ascorbic acid according to instrument’s operating procedure.

Weigh accurately a tablet of vitamin C and grind it to fine powder. Weigh about 0.01 g of this power accurately and transfer it into one 100 mL volumetric flask. Dilute with absolute alcohol to the mark.

 

Pipet 3.0 mL aliquot of this vitamin C solution, transfer it into a 25.00 mL volumetric flask (No.5), and dilute with absolute alcohol to the mark.

Obtain its absorption spectrum from 320 to 220 nm of the solution.

 

Calculations

Calculate the percentage of vitamin C in a tablet. Calculate the molar absorptivity (E) for ascorbic acid at the wavelength you selected. Discuss what part of the ascorbic acid molecule is accountable for the UV absorption.

 

 

 

 

 

 

Unit 2: EXPERIMENT 2. Quantitative Analysis of Multicomponent Samples

 

[See G. D. Christian, Analytical Chemistry, sixth edition, Wiley, page 478]

Theory

Quantitative spectrophotometric analysis of multicomponent samples with overlapping spectra can be achieved by chemometric techniques when the identities and the spectra of the components are known. The method is useful for applications where a well-defined process requires quality control monitoring.

For example, the absorbance of a solution, consisting of three components x, y , and z, at the wavelength (i) is the sum of absorbances of all species in the solution.

If the cell pathlength (l) is constant, then for a sample mixture that obeys Beer's law, the absorbance, Ai, at wavelength i is a linear sum:

where aij is the absorbance of pure component j per unit concentration, cj is the molar concentration of j in the mixture, and the sum is taken over all n absorbing components.

For measurements made at various wavelengths the system of simultaneous equations can be expressed in matrix form as:

A = [a] c

where A is a column vector composed from the measured absorbances of the mixture at r different wavelengths, [a] is an r X n matrix whose columns contain the spectra (per unit concentration) of the pure components, and c is column vector whose elements represent the concentrations of the n respective components. The concentration vector can be obtained by the least-squares pseudoinverse matrix computation:

c = [a]+A

Where [a]+ is the pseudoinverse of [a].

By ensuring that the number of wavelengths are greater than the number of components (r > n) the uncertainties in the concentrations can also be determined.

For example, the composition of a mixture containing Co, Ni and Cu can be determined in this way.

Equipment

* 10-mL volumetric pipets (3)

* 25-mL volumetric flasks (3)

* Matching cuvettes (2)

Reagents

* 0.05 M Co(NO3)2 stock solution

* 0.05 M CuSO4 stock solution

* 0.05 M Ni(NO3)2 stock solution

* Unknown mixture of the three components supplied by the laboratory instructor.

Procedure

(1) Turn on the U-3000 UV-VIS spectrophotometer according to instrument's operating procedure, and allow it to warm up.

(2) Prepare 0.02 M Cu(II), Co(II), and Ni(II) solutions by diluting the 0.05 M stock solutions with deionized water into three separate 25-mL volumetric flasks. (Caution: DO NOT contaminate the stock solutions, i.e., do not pipet directly from the stock solution bottles. Pour a little more than the required amount to a beaker and pipet the required volume)

 

(3) Rinse two matching glass cuvettes thoroughly with deionized water (never with cleaning detergents), and fill them with deionized water (avoid air bubbles in the cuvette). Holding the cuvette on the two opaque sides, wipe the two transparent sides to remove moisture, dust, and fingerprints. Insert the cuvettes, containing deionized water, into the REFERENCE and SAMPLE compartment respectively.

(4) Record absorption spectrum of the baseline (from 380 nm to 900 nm) as directed in instrument's operating procedure.

(5) Replace the solution in the SAMPLE compartment with the Cu(II) solution. (Be sure to rinse the cuvette with the Cu(II) solution several times before filling it. Wipe the cuvette, and check for air bubbles.) Record the baseline-corrected-spectrum (from 380 nm to 900 nm) according to instrument's operating procedure.

(6) Repeat steps 3 through 5 for Co(II) and Ni(II) solutions, respectively.

(7) Examine the spectra of Cu(II), Co(II), and Ni(II), and select three wavelengths for analyzing mixtures, and their baselines, of these three components.

(8) Measure accurately the absorbances of the three standard solutions at each of the three selected wavelengths.

(9) Obtain an unknown mixture from the Laboratory Instructor. Record the absorbances of the unknown at the three selected wavelengths.

Calculations

(1) Correct the absorbances of each sample for baseline.

(2) Tabulate your data and results according to data sheet given below.

(3) Use Excel to obtain the concentrations of Cu(II), Co(II), and Ni(II) in the unknown (consult your TA for details of the calculation).

DATA SHEET FOR UV-VIS EXPERIMENT 2 (Unit 2)

NAME:_______________________________PARTNER:________________________

DATE: ________LAB INSTRUCTOR’S SIGNATURE:___________________

Instrument (Model No.): ______________________________________

 

I. Preparation of Solutions

   

Calibration standards

  Conc. of Stock Solution

(mol/L)

Volume of Stock Solution

(mL)

Vol after dilution

(mL)

Conc after dilution

(mol/L)

Cu++ 0.05      
Co++        
Ni++        

Final volume =________________________________mL

  Wavelength Selected (nm)
Cu++  
Co++  
Ni++  

II. Spectral Absorbance Data

 

Calibration standards (measured absorbance)

Unknown Mixture
Wavelength (nm)

Cu2+

(abs)

Co2+

(abs)

Ni2+

(abs)

(abs)
         
         
         

III. Calculations

Calibration Matrix and Mixture Vector

 

Calibration standards (molar absorptivity, [M-1cm-1])1

Mixture
Wavelength (nm)

Cu2+

(abs/conc)

Co2+

(abs/conc)

Ni2+

(abs/conc)

(abs)
         
         
         

1Molar absorptivity is obtained by dividing absorbance by molar concentration, and path length in centimeters.

Concentration of Unknowns: (Use Excel; see Appendix)

A set of three simultaneous linear equations must be solved to obtain the concentration of Cu2+, Co2+, and Ni2+ in the unknown mixture. Do not worry if matrix mathematics is unfamiliar to you. However, you must know how Excel can assist you to carry out such complicated math effortlessly. First

Summary of results

 

True

Conc.

(mol/L)

Calc.

Conc.

(mol/L)

Cu2+

   

Co2+

   

Ni2+

   

 

 

 

 

Unit 3: Fourier Transform-Infrared Spectroscopy

 

 

Theory

Nearly all organic or inorganic compounds having covalent bonds absorb various frequencies of infrared radiation. Depending on the type of bonds present, a number of selected frequencies of IR radiation will be absorbed by a molecule.

 

With modern FT-IR instruments, it is relatively easy to record spectra from solids, liquids, gases and polymer films. In fact, a choice of sampling techniques exists for all states of matter. Some of the most common sample preparation methods are discussed in this section.

 

Techniques for Solids

(a) a solution in a suitable solvent such as CCl4,

(b) a suspension in liquid (mull),

(c) mixed and pressed into a alkali halide disc,

(d) reflectance techniques.

One of the easiest and the fastest methods to analyze a solid sample is by the mull technique. The solid sample is ground into a fine powder, suspended in a mineral oil such as Nujol, and the resulting mixture is ground to a smooth paste. Then, a small amount of paste is placed in between a pair of NaCl plates and the spectrum is recorded. The disadvantages to this technique are the lack of controlling the thickness of the paste in between the NaCl plates, and scattering of light by the solid particles. The latter can be minimized by using a liquid of the same refractive index as the solid sample.

The traditional technique of analyzing solid samples is by the Pellet Method. In this method, the sample is first ground into a fine powder. The powder is then mixed with dry KBr, and ground further. An agate mortar and pestle is normally used to grind the materials (agate is preferred since it is an inert material; KBr corrodes stainless steel). However, using an electrical mill for this purpose is much more convenient. A capsule made of polystyrene, stainless steel, or agate is used to contain the sample during the milling process. Stainless steel is popular, however, it should be noted that KBr will corrode this material. Small stainless steel balls are placed in the capsule with the sample and KBr and a stopper is used to close the capsule. The mill, depending on design, either vibrates the capsule, or rocks it back and forth at very high speed.

The finely ground material is then removed from the mill, placed in a KBr die and several tons of pressure is applied with a hydraulic press to coalesce the sample into a transparent or semi-transparent disk. Die sizes range from 1mm, for micro samples, up to the traditional 13mm diameter disks. When necessary, a vacuum line is connected to the die to remove entrained air, and to a limited extent, entrained moisture. As entrained moisture can cause the finished disk to be opaque the KBr powder should be kept dry by means of a desiccator or a heated oven. Moist samples are not suitable to this technique as they will cloud the disk. Such samples should be dried before analysis.

Assembly and Loading of Sample

Step 1

• Place the base on a flat surface and insert the ‘0-ring in the groove

• Place the die assembly over the post in the base.

• Insert the anvil POLISHED SIDE UP into the bushing of the die.

Step 2

• Load the prepared sample through the bushing hole and onto the anvil.

• Level the sample matrix material using a microspatula or a clean, dry, glass rod.

Step 3

• Place the second "0-ring" fl the groove and place the barrel on top.

• Insert the plunger and place the "0-ring" and washer around the plunger.

Pressing the Pellet

• Place the complete die in a hydraulic press and connect the vacuum line.

• After two minutes under vacuum, press the pellet.

• After an additional two minutes, release the pressure and the vacuum

• Wait one minute before removing the die from the press.

Conversion for 13mm Die:

lbs. total load = 0.205 x psi

Examples: 25,000 psi - 5125 lbs. total load (gauge reading)

Caution: DO NOT exceed 12,000 pounds total load on the gauge (60,000 psi at sample)

Techniques for Liquids

solution in a suitable solvent such as CCl4,

a thin film of pure liquid between salt plates,

(c) reflectance techniques.

Usually for liquid samples as a solution, a demountable sodium chloride cell is used. The cell consists of two NaCl plates situated in between two supporting metal plates. At the two ends of the cell, there are two openings which are used to fill up the cell. Spectra of neat liquids can be recoded as a thin film pressed between two salt plates.

Techniques for gases

a gas cell with alkali halide windows,

a solution in a suitable solvent.

Techniques for polymers

(e) a solution in a suitable solvent such as CCl4,

(f) a thin film,

(g) a thin film evaporated on an alkali halide plate,

(h) a thin slice cut from larger sample,

(i) reflectance techniques.

The use of Horizontal Attenuated Total Reflectance (HATR) in the characterization of Polymer Films

In the HATR system, a crystal of an IR transmitting material having a high refractive index, of 2.2 or more, is held in a horizontal plane. The IR beam from the spectrometer is directed into the crystal at an angle which exceeds the critical angle. Internal reflection takes place in the crystal. The sample is placed in optical contact with the surface at which this internal reflection occurs. At this reflection point, some energy is lost to the sample, corresponding to the absorption bands of the sample. The beam finally exits the crystal and mirrors of the accessory guide the IR the remaining energy to the instrument's detector.

 

For samples of films and polymers, a flat plate system is used. The sample is placed on the crystal and a sample clamp used to provide optical contact. The sample clamp normally has a facility which enables it to accommodate samples of varying thickness and also to provide a range of contact pressures to optimize the experiment, by controlling band intensity.

 

 

 

 

 

 

Unit 3, Experiment 1: Characterization of organic compounds as thin films by FT-IR

 

Equipment

JASCO FT/IR-460 spectrometer

 

 

Reagents

* Polystyrene, polyethylene, nylon, saran, Teflon, polyester, mylar, and any other available thin films.

* Bring samples of wool, synthetic fabric such as polyester, soda bottles and cans.

Procedure

Record infrared spectra of at least five different thin films and two kinds of fiber by horizontal attenuated total reflectance (ATR) technique using JASCO FT/IR-460 spectrometer. [use polyethylene, polystyrene, nylon, saran, Teflon,

Cut one square inch pieces for soda bottles and cans, and fabric material.

Final report

Interpret spectra you recorded. Write the chemical structures of the polymers used. Assign vibrations to least three major peaks in each spectrum.

Record spectra from at least three samples you brought from home. Identify the polymers as best as you can.

Write a one page report on how infrared spectroscopy is used in forensic investigations.

     

Recycling Symbols

   
CODE TYPE NAME

FORMULA

DESCRIPTION SOME EXAMPLES
PETE polyethylene terephthalate

usually clear or green, sinks in water, rigid, glossy soda bottles, peanut butter jars, vegetable oil bottles
HDPE high density polyethylene

semi-rigid, sinks in water milk and water jugs, juice and bleach bottles
PVC polyvinyl chloride

semi-rigid, glossy, sinks in water detergent / cleanser bottles, pipes
LDPE low density polyethylene

flexible, not crinkly 6-pack rings, bread bags, sandwich bags
PP polypropylene

semi-rigid, low gloss margarine tubs, straws, screw-on lids
PS polystyrene

often brittle, glossy styrofoam, packing peanuts, egg-cartons, foam cups

 

 

Unit 3, Experiment 2: Characterization of organic compounds as solutions by FT-IR

The objective of this experiment is to record spectra from solutions, and then identify functional groups present in an unknown chemical provide by your TA.

Equipment

* Perkin Elmer Paragon 1000PC Fourier-transform infrared spectrometer.

* Demountable sodium chloride cell

Reagents

* Carbon tetrachloride, cyclohexane, ethyl acetate, methyl ethyl ketone, (10 mL of each)

* Unknown (labeled UNK? supplied by the laboratory instructor)

Procedure

1) Record infrared spectra of cyclohexane, ethyl acetate, and methyl ethyl ketone using a demountable NaCl cell. Use air (cardboard cutout) as background. If spectra of neat liquids are out of range, adjust their concentrations by diluting them with CCl4. (about 5 to 10 times dilution).

2) Obtain the infrared spectrum of the unknown.

3) Correlate functional groups to absorption peaks observed in all the spectra.

4) Determine the functional groups present in the unknown, and identify to which class of compounds it belongs to (e.g. alkanes, alkenes, etc.).

Report

Present your spectra of cyclohexane, ethyl acetate, and methyl ethyl ketone in an appropriate Figure. Correlate major abortion bands and to functional groups of the compounds tested.

Unit 3, Experiment 3: Quantitative determination of Methyl Ethyl Ketone

The objective of this experiment is to determine the concentration of methyl ethyl ketone (MEK) in an unknown sample.

Theory: In the absence of chemical interactions, infrared absorbances should obey Beer’s Law, A = Elc, where A is the absorbance, E is the molar absorptivity, l is the path length, and c is the concentration. In this experiment you will prepare a standard curve by measuring the absorbance due to MEK in several standard solutions and plotting the data as absorbance vs. concentration. According to Beer’s Law, the plot should be linear. You will then record the spectrum of an unknown sample of MEK and utilize the standard curve to determine the unknown concentration.

Equipment

* Perkin-Elmer Paragon 1000PC Fourier-transform infrared spectrometer.

* Demountable sodium chloride cell

* 10 mL volumetric flasks (6)

* Syringe

Reagents

* Cyclohexane, methyl ethyl ketone, (10 mL of each)

* Solution of methyl ethyl ketone in cyclohexane of unknown concentration (labeled UNK-MEK? supplied by the laboratory instructor)

Procedure:

1) Prepare four standard solutions of MEK in cyclohexane of 0.3-1.5 % (v/v) range. Pure cyclohexane serves as the 0.0 % solution. Use the demountable liquid cell having a 0.2-mm gap between the NaC1 windows. The cell is filled using the glass syringe with a steel needle. The cell can be emptied using the plastic syringe to blow out any residual liquid. Clean the cell by flushing it with the organic solvent followed by the solution to be measured. Measure the most dilute solution first. Spent reagents, properly dispose to organic waste.

• Record a BACKGROUND scan using the empty demountable cell.

• Record a SCAN for each of the standards and the unknown. Save each spectrum.

• View the spectra in absorbance mode.

• Print a spectrum of the unknown only.

• Identify a peak whose size depends on the concentration of MEK.

• Overlay the spectra for the six standards and the unknown on one screen. Greatly expand the horizontal and vertical axes to obtain a view showing how the size of the peak of interest varies with concentration. Print this view.

• Select a frequency that is appropriate for quantification. Measure absorbance values at that frequency from the spectra of standards and that of the unknown.

• Use Excel to plot a calibration curve and calculate the concentration of MEK in the unknown solution.

Final report

• Determine the wavenumber of an absorption peak that is suitable for the quantitative analysis? On what basis did you select this peak? What functional group is responsible for this absorption peak?

• What relationship between absorbance and concentration is revealed from your data?

• What is the concentration of the unknown?

 

Unit 3, Experiment 4: IR Spectrum of benzoic acid

Equipment

* Perkin Elmer Paragon 1000PC Fourier-transform infrared spectrometer.

* KBr pellet apparatus (die, hydraulic press, grinder, etc.)

Reagents

* Potassium bromide

* Benzoic acid

* Nujol

Procedure

(1) The method of making a KBr pellet will be demonstrated by the laboratory instructor.

(2) Mix a few milligrams of benzoic acid with approximately 0.5 to 1 g of oven-dried KBr.

(3) Use a portion of this mixture to make the pellet, and obtain its spectrum.

(4) Grind approximately 0.1 g of benzoic acid into a fine powder.

(5) Add approximately 1 g of Nujol, and grind the mixture into a smooth paste.

(6) Place a small quantity of the paste in between two NaCl plates, and obtain its spectrum.

Final report

(1) Compare the spectrum of benzoic acid obtained by mull and KBr pellet techniques. Discuss the differences observed (if any).

Unit 4: Gas Chromatography

Chromatography is a physical method for separating mixtures. Generally, in any chromatographic separation there are two phases (solid, liquid or gas) that move relative to each other while maintaining intimate contact. The moving mobile phase carries analytes with it while the stationary phase tries to retain them. Retention of solutes by the stationary phase will cause solutes to migrate slower than the average velocity of the mobile phase. The extent to which this occurs is reflected in the retention time (Rt, the amount of time required for a analyte to appear at the end of a column of length) of a solute. Since some analytes may stay longer in the stationary phase than others, a separation is afforded.

In gas chromatography, vaporized analytes are transported thorough a column by a gaseous mobile phase (usually helium). The instrument used for the separation is called a gas chromatograph. Basic components of a typical instrument are a heated injector, a precisely temperature controlled oven, and a detector that responds to minute amounts of analytes that elute from the column.

The intensity versus time plot that is recorded is called a chromatogram.

Modern gas chromatography is conducted with open tubular capillary columns made of fused silica. Outside of the columns are coated with polyimide resin to give a certain degree of flexibility to the columns. Inner wall are coated with a very thin film of viscous liquid which acts as the stationary phase.

Useful Websites

http://www.chem.agilent.com/cag/cabu/whatisgc.htm

Prelab Question: 1) Clearly define the terms chromatography, chromatograph, chromatogram, and chromatographer.

Unit 4, Experiment 1: Gas chromatographic separation of a hydrocarbon mixture

Equipment

·28 GC Syringe (10 mL)

·29 Agilent 6890 Gas Chromatograph equipped with a flame ionization detector.

·30 HP-5 (5% phenyl methyl silicone) coated fused silica capillary column (30 m x 0.32 mm, 0.25 mm film thickness) (J&W Scientific)

·31

Reagents

A mixture of normal hydrocarbons (n-nonane to n-hexadeane) in hexane.

Unknown sample (supplied by the laboratory instructor.)

Procedure

Note column parameters, carrier gas flow rates, and temperature programs used for each experiment.

1) Inject 1 mL of the hydrocarbon mixture into the gas chromatograph, keep the oven temperature at 100 0C isothermal, and record a chromatogram for 25 min. After finishing the run, integrate the peak areas using the built in ChemStation software program. Identify the GC peaks by injecting a sample of a known hydrocarbon.

2) Inject 1 mL of the hydrocarbon mixture into the gas chromatograph, keep the oven temperature at 40 0C isothermal for 2 min, increase the oven temperature at 8 0C /min to 260 0C, and hold the temperature at 260 0C for 1 min. After finishing the run, integrate the peak areas using the built in ChemStation software program. Repeat the experiment one more time (measure 1 microliter of sample as accurate as you can).

3) Inject 1 mL of the unknown hydrocarbon solution using the same temperature gradient gas chromatographic conditions as in section 2 and record a chromatogram.

 

Final report

1) Make a Table listing data from the isothermal run (Retention time, log10 retention time, peak area, identification, carbon number).

2) Plot a graph retention time (y axis) versus the carbon number of hydrocarbons (x axis) from the isothermal run.

3) Plot a graph log10 retention time (y axis) versus the carbon number of hydrocarbons (x axis) from the isothermal run. Compare the two graphs, and comment on important differences and trends you observe.

4) Compare the chromatograms obtained under isothermal and temperature gradient conditions.

5) Find the average chromatographic peak area for each component (and SD) from the three chromatograms recorded under temperature gradient conditions. Find mean response per microliter of the solution per component. Plot a histogram with vertical error bars [carbon number x axis, response (= peak areas) y axis]. Comment on the errors observed.

6) Explain the following acronyms used in gas chromatography. WCOT, SCOT, PLOT, FID, and TCD.

Unit 4, Experiment 2: Gas chromatographic separation

To be added later.

 

Unit 5: High Pressure Liquid Chromatography

 

Modern liquid chromatographic separations are conducted with columns packed with very fine particles (3-5 mm). The use of a high pressure pump is required to force the mobile phase to pass through such columns (high pressure liquid chromatography, HPLC).

Two main classes of stationary phase are commonly used in HPLC.

1) Normal phase columns are usually packed with silica gel; they work in the adsorption mode in a manner similar to that of a silica gel column in conventional gravity chromatography. Since the stationary phase is polar, a more polar solvent has a higher eluent strength.  
2) Reversed phase chromatography is the most common form of HPLC. Frequently, reversed phase columns are packed with a chemically bonded octadecylsilyl coated silica; such columns are referred to as C-18 RP columns. Thus, stationary phase is nonpolar or weakly polar and the solvent used is more polar. In this case, a less polar solvent has a higher eluent strength.

 

 

Unit 5, Experiment 1: HPLC separation of a mixture of compounds

 

 

 

 

Equipment

 

·34 HPLC Syringe (50 mL)

·35 Agilent 1100 Liquid Chromatograph with a diode array UV detector.

 

Reagents

Reverse Phase Test Mixture.

Filtered HPLC grade solvents (methanol, water, acetonitrile).

Reverse Phase Test Mixture

name structure lmax (nm)
uracil  
acetophenone  
methyl benzoate  
toluene  
naphthalene  

 

 

Procedure

Note the column parameters (manufacturer; packing material; length and i.d), solvent flow rate and pressure, dimensions of the injector loop, and ambient temperature of the lab. Set up an acquisition data file in the computer. Set pump parameters for a 50:50 water:acetonitrile isocratic run. Learn from the instructor how the HPLC injection valve works. LOAD 10 mL of the Reverse Phase Test Mixture to the injection loop using a syringe. INJECT the sample. Record a chromatogram monitoring UV absorption at 254 nm. Print UV spectra of all components. Repeat the injections twice more. Integrate the chromatographic peak areas using the built in ChemStation software program.

Repeat the experiment thrice, each time injecting 40 mL Reverse Phase Test Mixture. Integrate the chromatographic peak areas using the built in ChemStation software program.

Final report

1) Using UV spectra you recorded, assign the chromatographic peaks to respective compounds. Comment on the elution order of compounds. Comment on why absorption maximas [lmax (nm)] are different for each compound (relate to structure).

2) Plot a histogram showing average peak areas and standard errors from 10 mL injections (one set of columns), and average peak areas and standard errors from 40 mL injections (another set of columns).

3) Compare the two sets of columns and comment on the important points (particularly, the standard errors) you observe.

Unit 5, Experiment 2: HPLC Determination of Caffeine in Beverages

About 90% of adult Americans consume caffeine in one form or another every day. In fact, more than half of all American adults consume more than 300 mg of caffeine every day, making it America's most popular drug by far. Caffeine is central nervous system stimulant. Caffeine containing products include coffee, tea, cola, chocolate, and many over the counter analgesics.

Reagents

Benzophenone (1.0 mM in water:acetnitrile 50:50)

Benzoic acid ((1.0 mM in water)

Caffeine (0.2 mM in water)

Determining Detector Response Ratios.

Procedure: Pipette 5.00 mL of each of 1.00 mM aqueous benzophenone (the internal standard), 0.200 mM caffeine and 1.00 mM benzoic acid into a 25 mL conical flask equipped with a ground glass joint. Mix well. Inject 30 microlitres onto the HPLC injection loop. Identify each peak by injecting solutions of the pure components individually.

From the chromatographic trace of the mixture, determine the ratio of the areas relative to that of the internal standard, and hence determine the relative molar response factors for caffeine and benzoic acid relative to the internal standard.

  Peak area Relative area (area of analyte/ area of IS) Ratio of conc. (con of analyte/conc of IS) Molar response ratio
caffeine        
benzoic acid        
benzophenone   1.00 1.00 1.00

Calibration curve

Prepare 4 solutions by mixing 10.00 mL of 0.2 mM benzophenone and 10.00 mL of 0.2 mM, 0.4 mM, 0.6 mM. or 0.8 mM caffeine solution.

Inject 30 microlitres of each calibration mixture onto the HPLC injection loop. Determine

Obtain about 10 mL of an appropriate beverage. Pipete 1.00 mL of the beverage into a 25 mL volumetric flask and make the solution up to the mark with the internal standard solution (0.2 mM benzophenone).

Inject 30 microlitres of the above solution and record an HPLC trace. Determine the relative peak area using the known concentration of the IS.

Final report

Present data in the form of a Table which clearly shows how the values were obtained.

Determine relative peak area and correct for the molar detection responses of the individual components.

Determine the concentration of caffeine and benzoic acid in the beverage sample.

===============================================================

 

Since the internal standard and the analyte do not aborb UV light in an identical manner, we must calculate the relative response factor (RRF).

Caffeine

Concentration (mM)

Chromatographic peak area of caffeine signal (arbitrary units) benzophenone

Concentration (mM)

Chromatographic peak area of benzophenone signal (arbitrary units) Areacaffeine

Areabenzophenone

Conc.caffeine

Conc.benzophenone

0.2 a1 0.2 A1 a1/ A1 1.0
0.4 a2 0.2 A2 a1/ A1 2.0
0.6 a3 0.2 A3 a1/ A1 3.0
0.8 a4 0.2 A4 a1/ A1 4.0
           

………..()

RRF can be determined by a plotting a graph Areacaffeine/ Areabenzophenone versus Conc.caffeine/Conc.benzophenone. The slope of this graph gives the Relative Response Factor (RRF). We must calculate this since the detector generally has a different response to each component. This means if the analyte and internal standard are of equal concentrations, the area under the analyte peak is F times smaller or larger than that of the internal standard peak.

Furthermore, to determine the concentration of an unknown solution, however, the dilution factors must be considered. Since 24.00 mL of 0.2 mM benzophonne was diluted to 25.00 mL, the new concentration must be calculated.

In this way, the concentration of caffeine solution that was injected to the HPLC can be calculated. However, this is not what is required. We need to know the caffeine concentration in the beverage.

Unit 6: Spectrofluorometry

Quinine is an alkaloid extracted from the bark of the cinchona tree, a plant indigenous to the eastern slopes of the Amazonian area of the Andes. Apparently, the name cinchona comes from the Countess of Chinchon, the wife of a viceroy of Peru, who was cured of a malarial type of fever by using an extract of the bark of this tree. Although quinine is not used as an anti-malarial drug anymore, it is presently added as the bitter flavoring agent to "tonic water."

C20H24N2O2

Molecular weight 324.44 (free base)

Synonyms: Quinine bisulfate, Quinine hydrogen sulfate, dihydrate
CAS No.: 804-63-7
Molecular Weight: 782.96
Chemical Formula: (C20H24N2O2)2H2SO4.2H2O

Quinine is a strongly fluorescing compound, especially in dilute solutions, and thus can be detected in trace amounts by fluorometry.

A spectrofluorometer is composed of two monochromators. With one the wavelength for excitation is selected. With the other the wavelength of fluorescence is selected. Fluorometric cuvettes are similar to those used in regular UV measurements. They are made of quartz. However, fluorometric cells are clear on all sides.

Unit 6, Experiment 1: Determination of Quinine in Tonic Water by Spectrofluorometry

Note: Parts-per-million (ppm) is mass-ratio unit. However, 1 ppm is equivalent to 1 mg/mL or 1 mg/L because the density of dilute aqueous solutions is nearly 1.00 g/mL.

 

Materials Checklist

Spectrofluorometer (Shimadzu RF-1501)

Fluorometeric cuvettes (1 cm quartz). (Are these cell any different from regular UV cells?)

Volumetric glassware.

Commercial tonic water.

Wash bottle with distilled water

Tissues

Sulfuric acid (0.05 M)

Quinine sulfate

Tonic water

 

Procedure

Preparation of stock and standard solutions.

 

i. Prepare a stock solution quinine by weighing accurately about 10 mg of quinine sulfate dihydrate, and transferring it into a 250 mL volumetric flask with 0.05 M H2SO4.

ii. Prepare 5 calibration samples of 0.1, 0.2, 0.6, 0.8, 1.0 ppm quinine solution by making appropriate dilutions with 0.05 M H2SO4.

iii. Pour about 10 mL of tonic water to a clean and dry beaker and shake it thoroughly to reduce effervescence as much as possible. Then pipette three 1 mL samples to three 250 mL volumetric flasks and make it up to the mark with 0.05 M H2SO4.

iv. Set the excitation wave length of the fluorometer to 247 nm, and measure fluorescence emission spectrum between 350 and 600 nm of the 1 ppm standard solution.

v. Measure the fluorescence intensities of the calibration samples.

vi. Make at least three measurements for each sample.

vii. Measure the fluorescence intensities of the diluted tonic water samples.

Calculations

Construct a calibration curve using Excel. Report the concentration of quinine in tonic water in ppm.

 

 

 

 

 

 

Unit 7: Polarimetry

Principles of Polarimetry

In geometry, a figure is considered chiral if it is not identical to its mirror image. Some molecules show also this property of chirality. In other words, the overall three-dimensional configuration a chiral molecule cannot be superimposed on its mirror image. Such nonsuperimposable isomers are called enantiomers. Such molecules often has a center of chirality. To correctly describe the three-dimensional arrangements of atoms around a chiral center, we use R and S nomenclature system proposed by Cahn, Ingold and Prelog. You are expected to know how assign configurations according to method using a set priority sequence rules.

S-(+)-carvone

bp 230oC

density 0.965 g/mL

primary odor component of caraway oil

 

 

R-(-)-carvone

bp 230oC

density 0.965 g/mL

primary odorant of spearmint oil

 

 

Our understanding of stereochemistry owes much to initial observation made by French scientist Jean Baptiste Biot in the early nineteenth century. He observed that when linearly polarized light passes through a solution containing chiral molecules, the direction of polarization can be changed. This phenomenon is called optical rotation or optical activity.

Dextrose, which another name for glucose, refers to the fact that it causes linearly polarized light to rotate to the right side. Similarly, levulose, commonly known as sucrose, causes the plane polarized light to rotate to the left. Invert sugar, formed by converting sucrose to a mixture of glucose and fructose, gets its name from the fact that the conversion causes the direction of rotation to "invert" from left to right.

The degree of rotation depends on the wavelength of the light (usually, the yellow sodium D line near 589 nm wavelength is used), the optical path length, the concentration of the solution, and the chemistry of the molecule. Under identical conditions, some molecules rotate polarized light more than the others do. In order measure how good chiral molecules rotate plane- polarized light, we define a term called the "specific rotation." In fact, the specific rotation is an intrinsic characteristic of a chemical similar to other properties such melting point, or solubility. By convention, the specific rotation of a chemical is defined as the observed rotation when light of a specified wavelength passes thorough through sample path length of one decimeter (1 dm = 10 cm) and a sample concentration of 1 g/mL.

l = is the length of the cell in decimters (1 dm = 10 cm)

measured at 20 0C using the yellow sodium D line near 589 nm wavelength.

C = concentration of the solution in g/mL.

Some properties of a few chiral sugars are given below.

Compound
D-glucose (mixture)

a-D-glucopyranose (36%)

(m. pt. 146 0C)

b-D-glucopyranose (64%)

( m. pt. 148-155 0C)

+52.7

 

 

+112.2

 

 

 

 

+18.7

D-galactose (mixture)

a-D-galactopyranose

b-D-galactopyranose

+80.2

+150.7

+52.8

Maltose (mixture)

a-D-maltopyranose

b-D-maltopyranose

+130.0

+173.0

+112.0

Sucrose +66.5

Both anomers of D-glucopyranose can be crystallized and isolated (why are they called anomers?). In fact, they are different compounds with different melting points. However, if a sample of anyone of these pure anomers is dissolved in water, the optical rotations slowly change and converge to a constant value. This phenomenon is called mutarotation. Mutarotation of cyclic sugars occurs via a reversible ring opening to form the open-chain aldehyde, followed by ring closure to form back one of the hemiacetal anomers.

For a pure substance in solution, if the color and path length are fixed and the specific rotation is known, the degree of rotation can be used to determine the concentration. Polarimetry measures the rotation of polarized light as it passes through an optically active fluid. The instrument used is called a polarimeter, which a tool of great importance to those who trade in or use sugar syrups in bulk. The measured rotation can be

used to calculate the value of solution concentrations. A polarimeter consists of a polarized light source, an analyzer, a graduated circle

to measure the rotation angle, and sample tubes.

 

Unit 7, Experiment 1: Determination of sucrose by polarimetry

 

Materials Checklist

Polarimeter (Rudolph Autopole IV)

http://www.rudolphresearch.com

Volumetric glassware.

Sucrose.

Wash bottle with deionized water

Unknown sucrose solution

Coke and diet coke

 

 

Procedure

Preparation of stock and standard solutions.

viii. Prepare a stock solution by measuring 10.000 g of sucrose and quantitatively transferring it to a 100.00 mL volumetric flask with deionized.

ix. Prepare 5 calibration samples of 1.0, 2.0, 4.0, 6.0, 8.0, 1.0% w/v solutions and mix them well.

x. Fill the polarimeter cell with deionized water and zero the instrument. Note pathlength of the cell.

 

 http://www.rudolphresearch.com/cells.htm

xi. Fill the polarimeter cell with each solution and measure the rotation using plane-polarized light of 436 nm wavelength.

xii. Fill the polarimeter cell with the unknown sugar solution and measure the rotation.

xiii. Measure optical rotation of coke and diet coke (make sure the beverages have been left open to purge all the carbon dioxide out)

 

Calculations

Construct a calibration curve using Excel. Report the concentration of unknown sugar solution in w/v percentage. Find the specific rotation of sucrose. Comment on the optical rotation values you recorded with coke and diet coke.

 

 

 

 

n fact, one name for glucose, dextrose, refers to the fact that it causes linearly polarized light to rotate to the right or dexter side. Similarly, levulose, more commonly known as sucrose, causes the plane of polarization to rotate to the left. Invert sugar, formed by converting sucrose to a mixture of glucose and fructose, gets its name from the fact that the conversion causes the direction of rotation to "invert" from left to right.

In polarimetry the rotation of polarized light is measured as it passes through a cell containing an optically active fluid. The measured rotation can be used to calculate the value of solution concentrations; especially substances such as sugars, peptides and volatile oils. A polarimeter consists of a polarized light source, an analyzer, a graduated circle to measure the rotation angle, and sample tubes.

The polarized light passes through the sample tube and exhibits angular rotation to the left (-) or right (+). On the side opposite the polarizer is the analyzer. Using optics, visual fields are manually adjusted by the user to measure the optical rotation angle

Polarimetry is a sensitive, nondestructive technique for measuring the optical activity exhibited by inorganic and organic compounds. A compound is considered to be optically active if linearly polarized light is rotated when passing through it. The amount of optical rotation is determined by the molecular structure and concentration of chiral molecules in the substance. Each optically active substance has its own specific rotation as defined in Biots law:

The polarimetric method is a simple and accurate means for determination and investigation of structure in macro, semi-micro and micro analysis of expensive and non-duplicable samples. Polarimetry is employed in quality control, process control and research in the pharmaceutical, chemical, essential oil, flavor and food industries. It is so well established that the United States Pharmacopoeia and the Food & Drug Administration include polarimetric specifications for numerous substances.

Polarimetry

Molecules that contain an asymmetric carbon atom have the ability to rotate plane polarized light. A polarimeter is a device that measures the angle that plane polarized light is rotated on passing through a solution. A polarimeter consists of a source of monochromatic light, a polarizer, a sample cell of known length, and an analyzer to measure the angle of rotation. The extent of polarization is related to the concentration of the optically active molecules in solution by the equation a = [a]lc, where a is the measured angle of rotation, [a] is the optical activity (which is a constant for each type of molecule), l is the pathlength and c is the concentration. The overall angle of rotation depends on the temperature and wavelength of light used and so these parameters are usually standardized to 20oC and 589.3 nm (the D-line for sodium). A calibration curve of a versus concentration is prepared using a series of solutions with known concentration, or the value of [a] is taken from the literature if the type of carbohydrates present is known. The concentration of carbohydrate in an unknown sample is then determined by measuring its angle of rotation and comparing it with the calibration curve.

measure the optical rotation angle.

Polarimeters offer high accuracies where precision is critical in

determining the concentration of samples. Cole-Parmer offers

manual polarimeters where you look through a viewing scope to

read values on a vernier scale, and semiautomatic polarimeters

that have a digital display. Polarimeters can measure in angle of

rotation (°), International Sugar Scale (°Z), or both.

"C" is the concentration of the sample as a percentage, "L" is the length

of the sample tube in decimeters (1 dm = 100 mm), "[ a ]" is the specific

rotatory power of the sample, usually found in a chemical reference book,

and "a" is the measured angle of rotation in degrees.

For example: A cane sugar solution is polarized in a 200-mm sample tube

and shows an angle of rotation of +15.0°. The specific rotatory power of

pure cane sugar is +66.5°. Using this equation, you can solve for sample

concentration (C).

C = 100 x 15.0 = 11.28%

2 x 66.5

Appendix

Frequently, the word analysis is used improperly even by experienced chemists. Only samples are analyzed. Elements, ions, and compounds are identified in a sample. It is correct to say that an analyst found traces of asbestos in a soil sample from a construction site. It is incorrect to say that asbestos was analyzed unless it means that the sample was asbestos (a so-called "pure" sample) and it was analyzed to determine the presence of impurities.

Rules for Significant Figures

Initial zeros are not significant. Because they are only used to locate a decimal place. The number 0.0777 has three, and 100.001 six significant figures, respectively.

Final Zeros. Zeros after a nonzero digit are significant only if a decimal point is present.

Final Zeros. Zeros after a nonzero digit are significant only if a decimal point is present.

Examples.

Number     Number of Significant Figures
7.77 x 104 =77700 7.77E+04 3
7.700 x 101 =77.00 7.700E+01 4
7.7000 x 102 =770.00 7.7000E+02 5
9.25 x 104 = 92500 9.25E+04 3
9.250 x 104 = 92500 9.250E+04 4
6.532 x 10-4 = 0.0006532 6.532E-04 4

 

Addition and subtraction. First carry out addition and subtraction, then round the answer to reflect the appropriate number of significant figures.

Examples:

24.35

+ 3.147

27.497 = 27.50

24.3

+ 3.137

27.437 = 27.4

In multiplying and dividing two measures numbers, the final product or quotient should bear the same number of significant digits as the least significant quantity in the problem.

Examples:

5.4 X 2.621 = 14.1534 = 14.1
4.234/2.34 = 1.8094017 = 1.81

Counting and measuring. A number obtained by counting has an infinite number of significant figures. There is no uncertainty when ten apples are in a bag whether it is 10.1 apples or 9.9 apples. Although we don’t bother to write it, the correct number is 10.00000000000000000000000.

Example: An apple weighs 50.12 g. The weight of 9 apples expressed in correct number of significant figures should be

9 X 50.12 g = 45.108 g = 45.11 g

 

 

Excel

We will use Excel spreadsheet program to record, calculate, and graph numerical data. Each final report should accompany a copy of the spreadsheet that was used.

Example:

Given below is spreadsheet from an experiment in which the weight was recorded each time after an addition of 1 milliliter of water from a burette to a beaker. The weight of the beaker was tared to zero at the beginning. The experiment was conducted in triplicate. Average weights and standard deviations were calculated using the functions available in Excel. In this example, slope gives the density of water. Always provide units when you report the slope and intercept. Together with the final lab report write up, a copy of the spreadsheet should be submitted as an appendix. Make sure the Row and Column numbers are included in your print out.

A B C D E F G
1
2 Weight of water per milliliter
3
4 weight of water recorded (g)  
5 determination I detrmination II determination III
6 Volume (mL) average weight (g) SD
7
8

1.00

1.0032

1.0045

1.2114

1.0730

0.1198

9

2.00

2.0150

2.2364

2.1009

2.1174

0.1116

10

3.00

3.0754

3.1307

2.9980

3.0680

0.0667

11

4.00

4.0065

4.1807

4.0097

4.0656

0.0997

13

5.00

5.0477

5.0028

5.2989

5.1165

0.1596

Formula: F8=AVERAGE(C8:E8)
Formula: G8=STDEV(C8:E8)

 

How to Print an Excel Spread sheet with Column and Row labels.

2. From the File menu, select Page Setup...
The Page Setup dialog box appears.

3. Select the Sheet tab

4. In Print Section, select Gridlines and Rows and Column headings.

5. You may also try the Fit to 1 Page Command in Page.

=========================================================================

You must learn how to add errors bars, insert Greek letters, superscripts and subscripts (Select the letters; Format; Cells, Subscript) in Excel charts.

 

Matrix determinant and Cramer’s Rule

We can use Matrix determinant and Cramer’s Rule to solve multiple equations. For example, we wish to find the values of x and y of the following system (equations 1 and 2).

x + 8y = 4 ………………..(1)

3x - y = -13 ………………(2).

Classically, we would solve equation 1 for x and apply that to equation 2 and find the answer. However, this procedure becomes too difficult when there are many equations and many unknowns. Matrix algebra provides an easier method.

A rectangular array of numbers such as

is called a matrix. This is a 3 by 3 matrix because it has three rows and three columns (An m by n matrix has m rows and n columns). In fact, this is a square matrix since it has the same number of rows and columns. It is matrix of order 3 since it has three rows and three columns. Each square matrix is associated with a number called the determinant.

=

Systems of three equations and three unknowns, x , y, and z, can be dealt in the same way. If D  0, the system has a unique solution, given by Cramer’s rule:

Example:

Evaluate the following determinant.

2

1

3

2

1

3

-1

-2

3

-1

2

3

1

2

3

-2

-4

27

-6

-12

3

2

1

3

2

1

3

-1

-2

3

-1

2

3

1

2

3

-2

-4

27

Add them up to find the determinant

Det A = -(-6) - (-12) -3 + (-2) + (-4) + 27 = 36

 

Excel provides such matrix calculations at a click of a button.

For example.

A

B

C

1

2

1

3

2

3

-1

-2

3

2

3

1

Click on any empty cell, click on "fx" in tool bar, and INSERT FUNCTION window will open.

Select the function MDETERM, and say OK.

Select the cells containing your matrix and say OK.

Alternatively, you may just type =MDETERM(A1:C3) in any cell. The matrix determinant is a number derived from the values in the array A1:C3.

For a three-row, three-column array, A1:C3, the determinant is defined as:

MDETERM(A1:C3) equals
A1*(B2*C3-B3*C2) + A2*(B3*C1-B1*C3) + A3*(B1*C2-B2*C1)

Cramer’s Rule

If D ≠ 0, the following system has a unique solution.

≠ 0

a11x + a12y = b1 ………………(1)

a21x + a22y = b2 ………………(2)

Equations 1 and 2 have two unknowns, x and y. Cramer’s rule states that x and y may be found from the formulas

This is best understood by working an example.

x + 8y = 4 ………………(3)

3x - y = -13 ……………(4) Solve this system and find values of x and y.

Answer:

First find the determinant of the coefficient matrix

= -1 – (8 x 3) = -25

= -4 - (-13 * 8) / -25 = -4

= 1

 

Pre Lab Exercises:

Find the following 3rd order determinant.

Answer = 30

Find the following 4th order determinant (use Excel).

Answer = -12

Solve the following systems of equations by Cramer’s rule.

a. 5x – 2y = 11 Answer x = 5, y = 7

2x + 3y = 31

 

Solve the following systems of equations by Cramer’s rule.

b. 2x – 1y -2z = 10 Answer x = 3, y = 2, z = -1

3x + 2y -z = 14

x + 3y +z = 8

=========================================================================

Logarithms and Antilogarithms

antilog (-6.82) = 10-6.82 = 10-6 x 100.18 = 0.15 x 10-6 = 1.5 x 10-7

Example 1: What is the pH of a 1.5 X 10-7 M H+ ion solution?

pH = -log(H+ ion concentration)

pH = -log(1.5 X 10-7)

In EXCEL you may write a cell function, =-LOG10(1.5E-7)

Which will return the answer 6.82.

Example 2: What is the H+ ion concentration of a solution pH of a 6.82?

In EXCEL you may write a cell function, =10^-6.82

Which will return the answer 1.5E-07

To add Mathematical Equations to Your Research Reports Use Microsoft Equation Editor

=============================================

You can insert a mathematical equation into Word, Excel, or PowerPoint, from Insert menu. However, you may have to install the program from you Office CD.

1. Insert your copy of Office CD in CD-ROM drive.

2. Open the Control Panel.

3. Double-click the Add/Remove Programs icon.

4. In the white box, locate the Microsoft Office entry that corresponds to what you have installed and click once to highlight it. For example, if you have Office XP, locate Microsoft Office XP Professional and select it.

5. Click the Change button. When the Office installation window opens, select Add or Remove Features, then click Next.

6. Next to Office Tools, click the + (plus sign) once. Click Equation Editor, and select Run from Computer.

7. Click Continue. When Equation Editor has finished installing, click OK.

======================================================

To enter a mathematical equation, do the following:

1. On the Insert menu, click Object.

2. In the working area into your document, and the Equation toolbar and menus will appear within the Office program’s window.

The equation you insert is an embedded object created by the Equation Editor program.

 

Final lab Report, Check list, and Grading codes

A) No abstract (-5 points)

B) Wrong numerical results, or no results (-5 points)

C) No final (numerical) results given in the abstract (-2 points)

D) Introduction too short, or insufficient description of the technique (-2 points).

E) Experimental. Instrumental names and sources of chemical are not given (-1 point). Incomplete sentences ((-1 point). Sentences not in past passive voice (-1 point).

F) Dilutions are not described in detail (-2 points).

G) Figures cut and pasted from external sources without giving proper credit (-2 points).

H) No Excel sheet (-5 points)

I) No cell and row numbers (-1 point)

J) No cell formulas (-2 points).

K) Wrong cell formulas (-1 point)

L) No Figures and Tables within the Results and Discussion section (-2 points). (Statements such as, "Please see attached sheets" are not acceptable)

M) No axes labels in Figures (-1 point for each occurrence)

N) No Figure or Table caption (-1 point).

O) Improper selection of axes scales (-1 point).

P) No units (-1 point for each occurrence)

Q) Wrong number of significant figures (-1 point).

R) Poor experimental results (-4 points).