Chapters 0-1: Measurements

WELCOME!

ELEMENTARY QUANTITATIVE ANALYSISCHEM 221

ELEMENTARY QUANTITATIVE ANALYSIS CHEM 221, Fall 2007

Tues & Thur 9:30-10:45, Rm. 112 Hamilton Hall

COURSE OUTLINE

Instructor: Dr. Robert Powers

Office LabsAddress: 722 HaH 720-721 HaHPhone: 472-3039 472-5316e-mail:[email protected] page: http://bionmr-c1.unl.edu/

Office Hours: 10:30-11:30 am MWF or by Special AppointmentI am in my office many other times during the week and am always willing to speak with you if you find me in or make an appointment.

Teaching Assistants:Ms. Jennifer Copeland phone: 472-5316 office: 721 HaHMs. Kelly Mercier phone: 472-5316 office: 721 HaHMr. Rob Waters contact: Resource center e-mail: [email protected]

http://bionmr-c1.unl.edu/

mailto:[email protected]

Course Work:Exam 1: 100 pts (Thurs., Sept. 20)Exam 2: 100 pts (Thurs., Oct. 18)Exam 3: 100 pts (Tues., Nov. 20)Final: 200 pts (10am-12pm, Wednesday, Dec. 19)Laboratory: 400 pts (due at end of each lab)Lab Notebook: 100 pts (due at end of semester)

Total: 1000 pts

Required Items:(i) Chem. 110 is the only prerequisite(ii) Text: "Quantitative Analysis" 7/e Daniel C. Harris, Freeman & Co., New York(iii) Lab Manual: "Laboratory Manual for Quantitative Chemical Analysis", J.D.Carr (2007)(iv) Laboratory Notebook: bound (not spiral), use one with grids instead of lined pages for graphs.(vi) Black Sharpie for labeling glassware(vii) Calculator for exams and lab (TI-89 style or a simpler model)(viii) Laptop (optional) to run Excel calculations during lab

Homework problem sets will not be collected or graded, but will aid your preparation for the exams.

COURSE OUTLINE

Lecture TopicsDate Chapter Topic ProblemsAug 28 Chap 0 & 1 Measurement 0-1,5-A,6 & 1-5,7,22,24,26 Aug 30 Chap 2 & 3 Tools 2-D,1,10,15, & 3-A,5,9,11 Sept 4 Chap 3 Error 3-12,13,15,18,21,23 Sept 6 Chap 27 Gravimetry 27-2,3,7,14,18,25,26 Sept 11 Chap 4 Statistics 4-B,E,2,3,6 Sept 13 Chap 4 Statistics (cont) 4-9,11,13,14,15,18,22 Sept 18 Chap 5 Calibration 5-A,B,C,22,23 Sept 20 EXAM 1Sept 25 Chap 6 Equilibrium (Intro) 6-A,B,G,I,K,1,2,3,5,13 Sept 27 Chap 6 Equilibrium (cont) 6-17,21,37,40,54 Oct 2 Chap 7 Titrations 7-B,C,D,1,2,4,8,11,13 Oct 4 Chap 8 Activity 8-A,C,1,4,8,14 Oct 9 Chap 8 Equilibrium (systematic) 8-F,G, H,10,16 Oct 11 Chap 8 Equilibrium (more) 8-18,8-21,8-23 Oct 16 Chap 8 Equilibrium (even more) 8-26, 28 Oct 18 EXAM 2Oct 22-23 Fall BreakOct 25 Chap 9 Monoprotic acid/base 9-B,C,G,H,4,6,10,13,19 Oct 30 Chap 9 Monoprotic (again) 9-24,26,27,29,30,36,37Nov 1 Chap 10 Polyprotic acid/base 10-A,1,2,4,7,9,16,23,29,31,33,38Nov 6 Chap 11 Acid/base Titrations 11-A,B,F,G,I,3,5,6,7,13,16 Nov 8 Chap 11 Acid/base Titrations (cont) 11-23,27,34,36,45,46,54,64 Nov 13 Chap 12 EDTA Titrations 12-B,2,4,5,6,13,22,28 Nov 15 Chap 14 Electrochemistry 14-B,D,I,2,3,15,18,25,41 Nov 20 EXAM 3Nov 22-23 ThanksgivingNov 27 Chap 15 Potentiometry 15-E,6,7,8,10,13,17,23,24 Nov 29 Chap 16 Redox Titrations 16-A,C,1,2,7,14,15,16,24Dec 4 Chap 18 Spectrophotometry 18-A,C,D,1,6,8,16,18,19 Dec 6 Chap 23 Separations 23-B,1,2,3,29, 44Dec 11 Chap 23 SeparationsDec 13 Chap 24 Gas Chromatography 24-A,B,C Dec 19 FINAL EXAM 10:00-12:00

Date Experiment ValueAug 27-31 Check-in, Safety, Introduction to Analytical Chemistry 0

Sep 4-7 Statistics (Exp 2) 50

Sep 10-14 Gravimetric Aluminum (Exp 3) 150

Sep 17-21 Gravimetric Aluminum (cont)

Sep 24-28 Volumetric Soda Ash (Exp 4) 200

Oct 1-5 Volumetric Soda Ash (cont)

Oct 8-12 Titration of Weak Acid & pK Determination (Exp 5) 100

Oct 15-19 Complexometric Titration for Water Hardness (Exp 6) 100

Oct 24-30 Potentiometric Titration of Iron (Exp 7 ) 100

Oct 31-Nov 6 Coulometric Analysis of Vitamin C (Exp 14 ) 100

Nov 7 – 13 Spectrophotometric Determination of Chromium and Cobalt (Exp 10 ) 100

Nov 14-21 Spectrophotometric Determination of Iron (Exp 11 ) 100

Nov 26-30 Gas chromatography of Aromatic Hydrocarbons (Exp 15 ) 100

Dec 3-7 Lab Make-up

Dec 10-14 Check out of lab

TOTAL 1100

Tentative Lab Schedule

Due to equipment limitations, experiments # 7, 10, 11, 14 & 15 will be taken in different order by portions of the students.

NOTE: Students having a Monday lab should make up Sept 4 lab on Sept 7 (Friday)

Scaled to 400 for final grade

COURSE OUTLINELectures:

ALL PowerPoint lecture notes are available online on BlackBoard and my web-site (http://bionmr-c1.unl.edu/).

!!!!The Lectures Notes Are Not Meant To Replace Attending Class!!!!!

Laboratory:

50% of your grade in CHEM 221 is based on your laboratory effort. You will be furnished samples whose composition is unknown to you. You will be asked to determine how much of a given analyte is present. You will be graded on how well you agree with the correct answer.

You are allowed to re-do one lab during the next to last week You are allowed to re-submit one lab calculation if you made a math mistake at no penalty to your lab grade:

you must clearly state what the mistake was and how you corrected it each subsequent resubmission of a calculation error will incur a progressive 10% penalty

• 2nd re-submission -10%, 3rd re-submission -20%, 4th re-submission -30% You will also be graded on how well you keep and maintain your lab notebook.

Good Lab Practice and Techniques are Essential



Lab Notebook Techniques The Lab Notebook Must:

State what was done. State what was observed Be understandable to someone else

Include Complete Description of Experiment: Purpose Methods Results Conclusions

Include Balanced Chemical Equations for Every Reaction Used

Paste Hardcopies of Important Data in Notebook

Include locations Where other Data is stored (computer files)

Notebooks are Legal Documents and Routinely Used for Patent Litigation

Laboratory Notebook should be bound (not spiral), use one with grids instead of lined pages for graphs.

Lab Notebook Techniques

This Notebook Page Has Precise Description with Adequate Detail

This Notebook Page is incomplete and a Useless Document. Limited Detail.

How to Read and Use a Buret

When reading a buret, it is important that your line of sight be in a direction perpendicular to the buret column.

All buret reading should be done using a buret card.


A constant dark reflection against a white background enables higher precision in determining relative titrant volumes.

Read volume associated with bottom of “meniscus”.

A 50 mL buret can be read to ±0.01 ml.

Upper limit of the black streak ought to be placed just under the meniscus, so that the bottom of the meniscus can be seen distinctly against a narrow zone of white.


A bubble in the nozzle of a buret will produce an inaccurate volume reading if the bubble escapes during a titration

The quickest way to get rid of bubbles is to fill the buret with titrant and open the valve.

Some bubbles may require “light” tapping to dislodge them.

Microsoft Excel Demo

Introduction to Analytical Chemistry

CSI: Crime Scene Investigation

Identifying an Unknown Is Not As Easy as Portrayed by the CSI TV Show.

Typically Requires More Than One Experiment and > 45 Minutes of Analysis with corresponding high cost (single DNA analysis ~$10,000)

Background

1.) Definition:

ANALYTICAL CHEMISTRY: The Science of Chemical Measurements.

2.) Types of Questions Asked in Analytical Chemistrya.) What is in the sample? (qualitative analysis)b.) How much is in the sample? (quantitative analysis)

3.) Techniques used in Analytical Chemistry:a.) Wet Chemical Methods: titrations, color-forming reactions, precipitations, etc.b.) Instrumental Methods: spectrometry, chromatography, etc.


What is it ? How much is there? How pure is it? What are the impurities?

Introduction to Analytical Chemistry The Analytical Process

1.) Formulating the Question:

Translate General Question into Specific QuestionIs this water safe to Drink? What is the concentration of Arsenic in the water sample?

2.) Selecting Analytical Procedures:a.) Choose procedure to measure Arsenic in water(i) Uncertainty in measurement(ii) Limit of detection(iii) Destroy sample(iv) Availability, time, cost b.) If necessary, develop new procedure

3.) Sampling:a.) Select representative material to analyze(i) don’t use the entire sample(ii) consistency in sample collection

Source Caffeine (mgs per serving

Serving size (oz)

Regular coffee 106-164 5

Decaffeinated coffee

2-5 5

Tea 21-50 5

Cocoa beverage 2-8 6

Baking chocolate

35 1

Sweet chocolate 20 1

Milk chocolate 6 1

soft drinks 36-57 12

The Analytical Process

4.) Sample Preparation:a.) convert sample into form suitable for chemical analysis

(i) Dissolve sample (ii) Concentrate sample

(iii) Remove species that interfere with analysis



4.) Sample Preparation:a.) Example:

M. Dahan et al., Science (2003) 302:442-445

How do you prepare samples for Drug Discovery?

What we want to know:• Is the drug active? Does it cure the disease/illness?• How is the drug taken? (Pill, injection)• How often does the drug need to be taken?• Does the drug have side-effects?

How these Questions are Typically Addressed:• Treat animal (rat, mice, etc) with drug• Monitor drug duration in animal• Monitor location of drug accumulation• Monitor animal health

How do you treat the animal with the drug?How do you monitor the drug concentration in the Animal?How do you determine the drug location?How do you determine the animals health?

Tumor size is measured by fluorescence through the mouse skin using quantum dots as a function drug dosage


4.) Sample Preparation:a.) Example:

How do you prepare samples for Drug Discovery?

Regulatory Toxicology and Pharmacology 31, S57–S62 (2000)

Tissue plug from mouse kidney

Cross-section of sacrificed mouse showing tissue removal

Chromatography indicates presence of drug an metabolites in tissue sample

Determine drug quantity and distribution

Inject mouse with drug


5.) Analysis:a.) measure concentration of analyte in several identical

aliquots (portions)(i) Replicate measurements uncertainty in the

analysis Avoid large errors Reliability of measurement

(ii) Calibration Curve Measure response for known samples

6.) Report and Interpretation of Results7.) Drawing Conclusions

a) How the Report is used

Units and Concentrations

Units of Measurement

1.) SI Units:a.) international units of measurement (metric units)b.) ALL SI units are based on certain fundamental

quantities

Quantity Unit (Symbol)

Length Meter (m)

Mass Kilogram (kg)

Time Second (s)

Electric current Ampere (A)

Temperature Kelvin (K)

Luminous intensity

Candela (cd)

Amount of substance

Mole (mol)

Plane angle Radian (rad)

Solid angle Steradian (sr)

To a large extent, analytical chemistry is a science of measurement and measurements require minimizing errors

Units and Concentrations

Standards of length were once represented by the distance between two marks on a solid metal bar. Copies of these standards were displayed in public places so that people could check the accuracy of the rules they were using.

In 1588, Elizabeth I issued a new standard yard which remained the legal British yard for over 300 years.

Standards Of Length (1876) Trafalgar Square

Units of Measurement

Units and Concentrations Units of Measurement

History of the meterOrigins of the meter go back to at least the 18th century• Two competing approaches to the definition of a standard unit of length.

define the meter as the length of a pendulum having a half-period of one second define the meter as one ten-millionth of the length of the earth's meridian along a quadrant

• (1791) French Academy of Sciences chose the meridian force of gravity varies slightly over the surface of the earth, affecting the period of the pendulum. meter equal 10-7 of the length of the meridian through Paris from pole to the equator.

prototype was short by 0.2 millimeters because researchers miscalculated the flattening of the earth due to its rotation.

• (1960) used a definition based upon a wavelength of krypton-86 radiation

• (1983) meter replaced by the following definition: The meter is the length of the path traveled by light in vacuum during a time interval of 1/299 792 458 of a second.

International Prototype Meter standard bar made of platinum-iridium


The Saga of Claude Émile Jean-Baptiste Litre

International System of Units uses the character "l" (lower-case L) to denote the metric unit of volume litre (liter).

It is often difficult to distinguish between the character "l" and the digit "1" in certain fonts or when handwritten. International System of Units only permits the use of a capital letter when the unit is named after a person.

Kenneth Woolner of the University of Waterloo perpetuated a hoax in the April 1978 issue of CHEM 13 News

Woolner created the fictional character of Claude Émile Jean-Baptiste Litre with a distinguished scientific career where he purportedly proposed a unit of volume measurement.

“since no such person existed for "L", it seemed reasonable that one should be invented. Reg suggested that I should write a "biography" for the April issue of CHEM 13 NEWS, and over the course of an evening (which included, I think I recall, most of a bottle of scotch) we generated much of the substance of an 18th century life, full of drama, revolution and romance.” – Dr. Woolner , 1988

1 liter


1.) SI Units:d.) To indicate multiples or fractions of units, various

prefixes are used

Prefix Symbol Factor

Mega M 106

Kilo k 103

Hecto h 102

Deca da 101

Deci d 10-1

Centi c 10-2

Milli m 10-3

Micro 10-6

Nano n 10-9

Pico p 10-12

Femto f 10-15

Atto a 10-18

Example:3.2x10-11 s = 32 x10-12 s = 32 ps


1.) SI Units:e.) conversions to SI unitsf.) Liter is commonly used for

volume instead of m3

Quantity Unit Symbol SI equivalent

Volume liter L *10-3 m3

milliliter mL *10-6 m3

Length angstrom Å *10-10 m

inch In. *0.0254 m

Mass pound lb *0.45359237 kg

metric ton *1000 kg

Force dyne dyn *10-5 N

Pressure bar bar *105 Pa

atmosphere atm *101325 Pa

torr Torr 133.322 Pa

pound/in2 psi 6894.76 Pa

Energy erg erg *10-7 J

electron volt eV 1.602176462x10-19 J

calorie, thermochemical cal *4.184 J

Calorie (British) Cal *1000 cal = 4.184 kJ

British thermal unit Btu 1055.06 J

Power horsepower 745.700 W

Temperature Centigrade (= Celsius) oC *K - 273.15

Fahrenheit oF *1.8(K – 273.15) + 32


2.) Expressions of Concentration:a.) Molarity (moles/L, or M):

(i) Most common unit of concentration Gives number of moles of a substance in 1 liter of the given solvent. Recall: 1 mole (mol) of a substance = 6.022 x 1023 units (atoms, molecules,

ions, etc). Molecular weight (MW): the mass of a substance that contains 1 mole. Example:

Find the concentration in Molarity (M) of 12.00g of benzene (C6H6) dissolved up to a total volume of 250.00 ml in hexane.

MW benzene = 6 * (12.011) + 6 * (1.008) = 78.114 g/mol

Conc. C6H6 = = 0.6144 M

No. C’s at. wt. C No. H’s at. wt. H

0.2500L)

78.114g1mol(12.00g)(

Make Sure Units Cancel!


2.) Expressions of Concentration:b.) Formality (F):

(i) Concentrations expressed in M describe the actual concentration of a given chemical species in solution.

(ii) Some chemicals when placed in solution will dissociate or converted to multiple forms Example:

(iii) Not convenient to refer to the concentrations of each individual form.(iv) Instead, concentration of total substance originally added to the solution is

used. Formal concentration or Formality given in (mol/L) Note: For compounds with a single form in solution, M = F

Acetic Acid:


2.) Expressions of Concentration:b.) Percent Composition:

(i) Weight Percent (wt/wt or w/w): Concentration expressed in terms of mass of substance versus the total mass of the sample.

(ii) Volume Percent (vol/vol or v/v): Concentration expressed in terms of volume of substance versus the total volume of the sample.

(iii) Weight-Volume Percent (wt/vol or w/v): Concentration expressed in terms of mass of substance versus the total volume of the sample.

)100(xsampletotalorsolutiontotalofmass

cetansubsofmasspercentWeight

)100(xsampletotalorsolutiontotalofvolume

cetansubsofvolumepercentVolume

)100(xsampletotalorsolutiontotalofvolume

cetansubsofmasspercentvolumeweight


2.) Expressions of Concentration:b.) Percent Composition:

(iv) Instead of expressing concentrations as a percentage, express in terms of: parts per thousand (ppt) – x103

parts per million (ppm) – x106

Parts per billion (ppb) – x109

3.) Solution Preparation:a.) Dilution of a Solution:

McVc = MdVd

where:Mc = Molarity of substance in the

concentrated solutionVc = volume of concentrated solution usedMd = desired Molarity of the diluted solutionVd = total volume of final diluted solution

Units and Concentrations Examples

How many grams of perchloric acid, HClO4, are contained in 37.6 g of 70.5 wt% aqueous perchloric acid? How many grams of water are in the same solution?

Units and Concentrations Examples

What is the maximum volume of 0.25M sodium hypochlorite solution(NaOCl, laundry bleach) that can be prepared by dilution of 1.00 L of 0.80 M NaOCl?

Chapters 0-1: Measurements

Documents

Transcript of Chapters 0-1: Measurements