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Analytical Chemistry
CHEM 2354

Analytical Chemistry
CHM 2354, Winter 2015
Schedule:
Monday LAB

14:30-18:30

Marion Hall (MRN)

Room: 301

Tuesday DGD
Thursday DGD
Thursday LEC
Tuesday LEC

14:30-15:30
14:30-15:30
08:30-10:00
10:00-11:30

HGN
FSS
Montpetit Hall (MNT)
Montpetit Hall (MNT)

Room: 302
Room: 2005
Room: 202
Room: 202

Instructor: Professor Maxim Berezovski
Office:
Address: D’Iorio Hall room 201
Phone: [phone] ext. 1898 e-mail: [e-mail] web page: http://mysite.science.uottawa.ca/mberezov/
Office Hours:
15:30-17:30 Tuesdays & Thursdays (after DGDs) 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.
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, mass spectrometry.

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

The table shows the extent to which industrial employers think students should have experience with various analytical techniques, as determined by the 2004 survey.

The Analytical Process
1.) Formulating the Question:
Translate General Question into Specific Question
Is this coffee strong?  What is the concentration of caffeine?

2.) Selecting Analytical Procedures:
a.) Choose procedure to measure caffeine
•
Sample preparation
•
Uncertainty in measurement
•
Limit of detection
•
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

Kazuki Yamamoto is a Japanese barista who constructs eye­popping works of 3D art using just foam and coffee.

Try Asking for One of These at Starbucks
Within the six years Yamamoto has been working at a coffee shop in Osaka, he's racked up more than 100,000 Twitter followers obsessed with his latte art.

Sometimes One Cup Is Not Enough
Some of his creations even climb out of their cups and reach out to others ( I'm afraid those fish are not long for this world…)

Introduction to Analytical Chemistry
The Analytical Process
4.) Sample Preparation:
a.) convert sample into form suitable for chemical analysis
(i) Remove species that interfere with analysis
(ii) Dissolve sample
(iii) Concentrate sample

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


How the Report is used

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)

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

Units of Measurement
1.) SI (International System of Units) from the French Le Système
International d'Unités:
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
1.) SI Units:
c.) 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



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:
d.) conversions to SI units
e.) 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)

o

Fahrenheit

o

C

*K - 273.15

F

*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 = 6.022 141 29 x 10 23 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 (C 6H6) 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

1mol
)
= 0.6144 M
78.114g
0.25000L

Conc. C6H6 = (12.00g)(

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:
c.) 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 tan ce x ( 100 ) mass of total solution or total sample

volume of subs tan ce 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 tan ce x ( 100 ) volume of total solution or total sample

Units and Concentrations
Units of Measurement
2.) Expressions of Concentration:
d.) 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
If a DILUTE solution has a concentration of 1 ppm, it would be approximately 1 mg/L or 1 µg/mL (valid if dmix= 1.0 g/mL)


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

Serial dilution is the stepwise dilution of a substance in solution. Usually the dilution factor at each step is constant, resulting in a geometric progression of the concentration in a logarithmic fashion.
Serial dilutions are used to accurately create highly diluted solutions as well as solutions for experiments resulting in concentration curves with a logarithmic scale.

Chemical Equilibrium
Introduction
1.)

Equilibria govern diverse phenomena


2.)

Protein folding, acid rain action on minerals to aqueous reactions

Chemical equilibrium applies to reactions that can occur in both directions:






reactants are constantly forming products and vice-versa
At the beginning of the reaction, the rate that the reactants are changing into the products is higher than the rate that the products are changing into the reactants.
When the net change of the products and reactants is zero the reaction has reached equilibrium.

First, system reaches equilibrium
Then, system continually exchanges products and reactants, while maintaining equilibrium distribution.

Reactants

Product

At equilibrium the amount of reactants and products are constant, but not necessarily equal

Chemical Equilibrium
Equilibrium Constant
1.) The relative concentration of products and reactants at equilibrium is a constant. 2.) Equilibrium constant (K):


For a general chemical reaction

c

Equilibrium constant:

K

d

[C ] [ D]

[ A]a [ B ]b

Where:
- small superscript letters are the stoichiometry coefficients
- [A] concentration chemical species A relative to standard state

Chemical Equilibrium
Equilibrium Constant
2.) Equilibrium constant (K):



A reaction is favored when K > 1
K has no units, dimensionless
- Concentration of solutes should be expressed as moles per liter (M).
- Concentrations of gases should be expressed in bars. express gas as Pgas, emphasize pressure instead of concentration
► 1 bar = 105 Pa; 1 atm = 1.01325 bar
►

- Concentrations of pure solids, pure liquids and solvents are omitted
► are unity
► standard

state is the pure liquid or solid

3.) Manipulating Equilibrium Constants
Consider the following reaction:

[ H  ][ A ]
K1 
[ HA]

Reversing the reaction results in a reciprocal equilibrium reaction:

K '1 

[ HA]




[ H ][ A ]

1 / K 1

Chemical Equilibrium
Equilibrium Constant
3.) Manipulating Equilibrium Constants
If two reactions are added, the new K is the product of the two individual K values:

K1
K2
K3

[ H  ][ A ]
K1 
[ HA]

K2 

[CH  ]
[ H  ][C ]

[ A ][CH  ]
K3 
[ HA][C ]

[ H  ][ A ] [CH  ] [ A ][CH  ]
K 3 K1K 2 



[ HA]
[ HA][C ]
[ H ][C ]

Chemical Equilibrium
Equilibrium Constant
3.) Manipulating Equilibrium Constants

Example:
Given the reactions and equilibrium constants:
Kw= 1.0 x 10-14
KNH3= 1.8 x 10-5
Find the equilibrium constant for the reaction:

Solution:
K1=
Kw
K2=1/KNH3
K3=Kw*1/KNH3=5.6x10-10

Chemical Equilibrium
Le Châtelier’s Principal
1.) What Happens When a System at Equilibrium is Perturbed?


Change concentration, temperature, pressure or add other chemicals



Equilibrium is re-established
-

-

Reaction accommodates the change in products, reactants, temperature, pressure, etc.
Rates of forward and reverse reactions re-equilibrate

Chemical Equilibrium
Le Châtelier’s Principal
1.) What Happens When a System at Equilibrium is Perturbed?


Le Châtelier’s Principal:
If a system in equilibrium is disturbed, the direction in which the system proceeds back to equilibrium is such that the disturbance is partially offset.

Consider this reaction:
At equilibrium:

Add excess CO(g):

To return to equilibrium
(balance), some (not all)
CO and H2 are converted to CH3OH

If all added CO was converted to CH3OH, then reaction would be unbalanced by the amount of product

Chemical Equilibrium
Le Châtelier’s Principal
2.) Example:
Consider this reaction:

K

[ Br - ][Cr2O 72- ][ H  ]8
[ BrO3- ][Cr 3 ]2

1 10 11 at 25 o C

At one equilibrium state:

[H  ] 5.0 M [Cr2O 72- ] 0.10 M [Cr 3 ] 0.0030 M
[Br  ] 1.0 M [BrO3- ] 0.043 M

Chemical Equilibrium
Le Châtelier’s Principal
2.) Example:
What happens when:

[Cr2O 72- ] increased from 0.10 M to 0.20 M
According to Le Châtelier’s Principal, reaction should go back to left to off-set dichormate on right:

Use reaction quotient (Q), Same form of equilibrium equation, but not at equilibrium: Q

[ Br - ][Cr2O 72- ][ H  ]8
[ BrO3- ][Cr 3 ]2


1.0  0.20  5.0  8

 0.043  0.0030  2

 2 10 11  K

Chemical Equilibrium
Le Châtelier’s Principal
2.) Example:
Because Q > K, the reaction must go to the left to decrease numerator and increase denominator.
Continues until Q = K:
1. If the reaction is at equilibrium and products are added (or reactants removed), the reaction goes to the left

2. If the reaction is at equilibrium and reactants are added ( or products removed), the reaction goes to the right

Chemical Equilibrium
Le Châtelier’s Principal
3.) Affect of Temperature on Equilibrium
Combine Gibbs free energy and Equilibrium Equations: o 
G

  H o  TS 
RT e
RT
K e

e
e



o

H


 H o

RT
RT

 S

e

R

S o


R

Only Enthalpy term is temperature dependent:

K(T )  e

 H o

RT

Chemical Equilibrium
Le Châtelier’s Principal
3.) Affect of Temperature on Equilibrium
1. Equilibrium constant of an endothermic reaction (Ho = +) increases if the temperature is raised.



H = +

2. Equilibrium constant of an exothermic reaction (Ho = -)decreases if the temperature is raised.



H = -

Chemical Equilibrium
Le Châtelier’s Principal
4.)

Thermodynamics vs. Kinetics


Thermodynamics predicts if a reaction will occur
-



determines the state at equilibrium

Thermodynamics does not determine the rate of a reaction
-

Will the reaction occur instantly, in minutes, hours, days or years?

G = spontaneous

Diamonds
-

Graphite

While reaction is spontaneous, takes millions of years to occur

Key Equations