Transcript Chapters 0-1: Measurements

WELCOME!
ELEMENTARY QUANTITATIVE ANALYSIS
CHEM 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
Address: 722 HaH
Phone: 472-3039
e-mail:[email protected]
web page: http://bionmr-c1.unl.edu/
Labs
720-721 HaH
472-5316
Office Hours: 10:30-11:30 am MWF or by Special Appointment
I 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
Ms. Kelly Mercier
Mr. Rob Waters
phone: 472-5316
office: 721 HaH
phone: 472-5316
office: 721 HaH
contact: Resource center e-mail: [email protected]
COURSE OUTLINE
Required Items:
(i)
(ii)
(iii)
(iv)
Chem. 110 is the only prerequisite
Text: "Quantitative Analysis" 7/e Daniel C. Harris, Freeman & Co., New York
Lab Manual: "Laboratory Manual for Quantitative Chemical Analysis", J.D.Carr (2007)
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
Course Work:
Exam 1:
Exam 2:
Exam 3:
Final:
Laboratory:
Lab Notebook:
Total:
100 pts
100 pts
100 pts
200 pts
400 pts
100 pts
1000 pts
(Thurs., Sept. 20)
(Thurs., Oct. 18)
(Tues., Nov. 20)
(10am-12pm, Wednesday, Dec. 19)
(due at end of each lab)
(due at end of semester)
Homework problem sets will not be collected or graded, but will aid
your preparation for the exams.
Lecture Topics
Date Chapter
Aug 28
Aug 30
Sept 4
Sept 6
Sept 11
Sept 13
Sept 18
Sept 20
Sept 25
Sept 27
Oct 2
Oct 4
Oct 9
Oct 11
Oct 16
Oct 18
Oct 22-23
Oct 25
Oct 30
Nov 1
Nov 6
Nov 8
Nov 13
Nov 15
Nov 20
Nov 22-23
Nov 27
Nov 29
Dec 4
Dec 6
Dec 11
Dec 13
Dec 19
Chap 0 & 1
Chap 2 & 3
Chap 3
Chap 27
Chap 4
Chap 4
Chap 5
Chap 6
Chap 6
Chap 7
Chap 8
Chap 8
Chap 8
Chap 8
Chap 9
Chap 9
Chap 10
Chap 11
Chap 11
Chap 12
Chap 14
Chap 15
Chap 16
Chap 18
Chap 23
Chap 23
Chap 24
FINAL EXAM 10:00-12:00
Topic
Problems
Measurement
Tools
Error
Gravimetry
Statistics
Statistics (cont)
Calibration
EXAM 1
Equilibrium (Intro)
Equilibrium (cont)
Titrations
Activity
Equilibrium (systematic)
Equilibrium (more)
Equilibrium (even more)
EXAM 2
Fall Break
Monoprotic acid/base
Monoprotic (again)
Polyprotic acid/base
Acid/base Titrations
Acid/base Titrations (cont)
EDTA Titrations
Electrochemistry
EXAM 3
Thanksgiving
Potentiometry
Redox Titrations
Spectrophotometry
Separations
Separations
Gas Chromatography
0-1,5-A,6 & 1-5,7,22,24,26
2-D,1,10,15, & 3-A,5,9,11
3-12,13,15,18,21,23
27-2,3,7,14,18,25,26
4-B,E,2,3,6
4-9,11,13,14,15,18,22
5-A,B,C,22,23
6-A,B,G,I,K,1,2,3,5,13
6-17,21,37,40,54
7-B,C,D,1,2,4,8,11,13
8-A,C,1,4,8,14
8-F,G, H,10,16
8-18,8-21,8-23
8-26, 28
9-B,C,G,H,4,6,10,13,19
9-24,26,27,29,30,36,37
10-A,1,2,4,7,9,16,23,29,31,33,38
11-A,B,F,G,I,3,5,6,7,13,16
11-23,27,34,36,45,46,54,64
12-B,2,4,5,6,13,22,28
14-B,D,I,2,3,15,18,25,41
15-E,6,7,8,10,13,17,23,24
16-A,C,1,2,7,14,15,16,24
18-A,C,D,1,6,8,16,18,19
23-B,1,2,3,29, 44
24-A,B,C
Tentative Lab Schedule
Date
Experiment
Aug 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)
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
Due to equipment limitations, experiments # 7, 10, 11, 14 & 15 will
be taken in different order by portions of the students.
Value
200
TOTAL 1100
Scaled to 400 for final grade
NOTE: Students having a Monday lab should make up Sept 4 lab on Sept 7 (Friday)
COURSE OUTLINE
Lectures:
ALL PowerPoint lecture notes are available online on BlackBoard and my website (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 is
incomplete and a Useless
Document. Limited Detail.
This Notebook Page Has
Precise Description with
Adequate 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.
How to Read and Use a Buret
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.
Read volume associated with bottom of
“meniscus”.
A 50 mL buret can be read to ±0.01 ml.
A constant dark reflection
against a white background
enables higher precision in
determining relative titrant
volumes.
How to Read and Use a Buret
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
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)
CSI: Crime Scene Investigation
Introduction to Analytical Chemistry
Background
1.) Definition:
ANALYTICAL CHEMISTRY: The Science of Chemical Measurements.
2.) Types of Questions Asked in Analytical Chemistry
a.) 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 Question
Is 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
Introduction to Analytical Chemistry
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
Introduction to Analytical Chemistry
The Analytical Process
4.) Sample Preparation:
a.) Example:
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
How do you
Animal?
How do you
How do you
treat the animal with the drug?
monitor the drug concentration in the
Tumor size is measured by fluorescence
through the mouse skin using quantum
dots as a function drug dosage
determine the drug location?
determine the animals health?
M. Dahan et al., Science (2003) 302:442-445
Introduction to Analytical Chemistry
The Analytical Process
4.) Sample Preparation:
a.) Example:
How do you prepare samples for Drug Discovery?
Cross-section of sacrificed
mouse showing tissue
removal
Inject mouse with
drug
Tissue plug from
mouse kidney
Chromatography indicates presence of drug
an metabolites in tissue sample
Determine drug quantity and distribution
Regulatory Toxicology and Pharmacology 31, S57–S62 (2000)
Introduction to Analytical Chemistry
The Analytical Process
5.) Analysis:
a.) measure concentration of analyte in several identical
aliquots (portions)
(i) Replicate measurements  uncertainty in the
analysis


(ii)
Avoid large errors
Reliability of measurement
Calibration Curve

Measure response for known samples
6.) Report and Interpretation of Results
7.) Drawing Conclusions
a)
How the Report is used
Units and Concentrations
To a large extent, analytical chemistry is a science of measurement
and measurements require minimizing errors
60
50
40
30
20
10
0
ia
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)
us
s
U
K
1970
1980
1990
R
A
us
Be tria
lg
i
C
ze C um
ch an
R ad
ep a
u
D bl i
en c
m
a
Fi rk
nl
an
Fr d
a
G nc
er e
m
an
Is y
ra
N el
or
w
Sl
a
ov
P
ak ol y
R and
ep
ub
lic
Sp
Sw ain
ed
en
kg/person
Sugar Consumption
Units of Measurement
1.) SI Units:
a.) international units of measurement (metric units)
b.) ALL SI units are based on certain fundamental
quantities
Units and Concentrations
Units of Measurement
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.
Standards Of Length (1876) Trafalgar Square
In 1588, Elizabeth I issued a new standard yard which remained
the legal British yard for over 300 years.
Units and Concentrations
Units of Measurement
History of the meter
Origins 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
Units and Concentrations
Units of Measurement
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.

1 liter
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
Units and Concentrations
Units of Measurement
1.) SI Units:
d.) To indicate multiples or fractions of units, various
prefixes are used
Example:
3.2x10-11 s = 32 x10-12 s = 32 ps
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
m
10-6
Nano
n
10-9
Pico
p
10-12
Femto
f
10-15
Atto
a
10-18
Units and Concentrations
Units of Measurement
1.) SI Units:
e.) conversions to SI units
f.) Liter is commonly used for
volume instead of m3
Quantity
Volume
Length
Mass
Unit
Symbol
SI equivalent
liter
L
*10-3 m3
milliliter
mL
*10-6 m3
angstrom
Å
*10-10 m
inch
In.
*0.0254 m
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
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
Energy
Power
horsepower
745.700 W
Temperature
Centigrade (= Celsius)
oC
*K - 273.15
Fahrenheit
oF
*1.8(K – 273.15) + 32
Units and Concentrations
Units of Measurement
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
No. C’s
at. wt. C
No. H’s
at. wt. H
1m ol
)
78.114g
Conc. C6H6 = (12.00g)(
= 0.6144 M
0.2500L
Make Sure Units Cancel!
Units and Concentrations
Units of Measurement
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:
Acetic Acid:
(iii)
(iv)
Not convenient to refer to the concentrations of each individual form.
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
Units and Concentrations
Units of Measurement
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.
Weight percent 
(ii)
Volume Percent (vol/vol or v/v): Concentration expressed in terms of volume of
substance versus the total volume of the sample.
Volume percent 
(iii)
mass of subs tance
x( 100 )
mass of total solution or total sample
volume of subs tance
x( 100 )
volume of total solution or total sample
Weight-Volume Percent (wt/vol or w/v): Concentration expressed in terms of
mass of substance versus the total volume of the sample.
weight  volume percent 
mass of subs tance
x( 100 )
volume of total solution or total sample
Units and Concentrations
Units of Measurement
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 solution
Vc = volume of concentrated solution used
Md = desired Molarity of the diluted solution
Vd = 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?