Announcements

1
Announcements

• Homework
• Chapter 4
• 8, 11, 13, 17, 19, 22
• Chapter 6
• 6, 9, 14, 15

• Exam
• Next Thursday

2
Comparison of Means with Students t

• A t test is used to compare one set of
  measurements with another to decide whether or
  not they are The Same
• Compare measured result with a true value
• Comparing two experimental means

3
Comparison of Means with Students t
Experimental Mean Bromothymol Blue
Are the end-points different?
Experimental Mean Erthyrosine
First you must ask, is there a significant
difference in their _____________________?
YES
NO
4
Comparison of Standard deviations between data

• The F-test may be used to provide insights into
• Whether there is a difference in the precision of
  two methods.
• (may warrant a new calculation to compare means!
  )
• Is method A more precise than method B?

5
F-test (comparison of std. dev.)
We always put the larger standard deviation in
the numerator, so that Fcalcgt1. If Fcalculated gt
Ftable then the difference is significant at the
95 CL.
6
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7
Throwing out Bad data
8
For an analysis of alcohol content in wine

• Dr. Skeels finds the following
• 12.51,
• 12.56,
• 12.47,
• 12.67,
• and 12.48

9
Q-test for Bad Data

• Compare to Qcritical
• Qcalc gt Qcritical can reject

10
Range

• 12.47 12.48 12.51 12.56 12.67

Gap
11
(No Transcript)
12
Recommended treatment of Outliers (When good Data
goes BAD)

• Reexamine carefully all data relating to the
  outlying result to see if a gross error could
  have affected its value.
• If possible, estimate the precision that can be
  reasonably expected.
• Repeat the analysis if sufficient sample and time
  are available.
• If more data cannot be secured, apply the Q test
  to the existing set to see if doubtful result
  should be retained or rejected based on
  statistical grounds
• If the Qtest indicates retention, consider
  reporting the median instead of the mean.

13
The minute paper

• Please answer each question in 1 or 2 sentences
• What was the most useful or meaningful thing you
  learned during this session?
• What question(s) remain uppermost in your mind as
  we end this session?

14
Chapter 6

• Chemical Equilibrium

15
Chemical Equilibrium

• Equilibrium Constant
• Equilibrium and Thermodynamics
• Enthalpy
• Entropy
• Free Energy
• Le Chateliers Principle
• Solubility product (Ksp)
• Common Ion Effect
• Separation by precipitation
• Complex formation

16
Equilibrium Constant

• aA bB . . . ltgt cC dD . . .

17
Evaluating an Equilibrium Constant

• 1. The concentrations of solutes should be
  expressed as moles per liter.
• 2. The concentrations of gases should be
  expressed in atmospheres.
• 3. The concentrations of pure solids, pure
  liquids, and solvents are omitted because they
  are unity.

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ManipulatingEquilibrium Constants

• HA H A-

19
ManipulatingEquilibrium Constants

• H A- HA

20
Adding Equilibrium Expressions

• Consider an acid that donates its proton to
  another atom.

K1
K2
HA C ? C H A-
K3 ?
21
ManipulatingEquilibrium Constants
HA C ? C H A-
K3 ?
22
Example

• The equilibrium constant for the reaction
• H2O H OH-

Kw 1.0 x 10-14
KNH3 1.8 x 10-5
K3 ?
23
Equilibrium and Thermodynamics

• A brief review

24
Equilibrium and Thermodynamics

• enthalpy gt H
• enthalpy change gt DH
• exothermic vs. endothermic
• entropy gt S
• free energy
• Gibbs free energy gt G
• Gibbs free energy change gt DG

25
Equilibrium and Thermodynamics

• DGo DHo - TDSo
• DGo -RT ln (K)
• K e-(DGo/RT)

26
Equilibrium and Thermodynamics

• The case of HCl
• HCl H Cl-

K?

• DHo -74.83 x 103 J/mol
• DS0 -130.4 kJ/mol
• DGo DHo - TDSo

27
Equilibrium and Thermodynamics

• The case of HCl
• HCl H Cl-

K?

• DGo (-74.83 kJ/mol) (298.15 K) (-130.4
  kJ/mol)
• DGo -35.97 kJ/mol

28
Predicting the direction in which an equilibrium
will initially move

• LeChateliers Principle and Reaction Quotient

29
Le Chatelier's Principle

• If a stress, such as a change in concentration,
  pressure, temperature, etc., is applied to a
  system at equilibrium, the equilibrium will shift
  in such a way as to lessen the effect of the
  stress.
• Stresses
• Adding or removing reactants or products
• Changing system equilibrium temperature
• Changing pressure (depends on how the change is
  accomplished

30
Consider

• 6CO2 (g) 6 H2O(g) C6H12O6(s) 6O2(g)

Predict in which direction the equilibrium moves
as a result of the following stress
Increasing CO2
31
Consider

• 6CO2 (g) 6 H2O(g) C6H12O6(s) 6O2(g)

Predict in which direction the equilibrium moves
as a result of the following stress
Increasing O2
32
Consider

• 6CO2 (g) 6 H2O(g) C6H12O6(s) 6O2(g)

Predict in which direction the equilibrium moves
as a result of the following stress
Decreasing H2O
33
Consider

• 6CO2 (g) 6 H2O(g) C6H12O6(s) 6O2(g)

Predict in which direction the equilibrium moves
as a result of the following stress
Removing C6H12O6(s)
34
Consider

• 6CO2 (g) 6 H2O(g) C6H12O6(s) 6O2(g)

Predict in which direction the equilibrium moves
as a result of the following stress
Compressing the system
35
Consider

• 6CO2 (g) 6 H2O(g) C6H12O6(s) 6O2(g)

DH 2816 kJ
Predict in which direction the equilibrium moves
as a result of the following stress
Increasing system temperature
36
Consider this

• CoCl2 (g) Co (g) Cl2(g)
• When COCl2 is 3.5 x 10-3 M, CO is 1.1 x 10-5
  M, and Cl2 is 3.25 x 10-6M is the system at
  equilibrium?
• Q Reaction quotient

K2.19 x 10-10
37
Compare Q and K
Q ____________ K 2.19 x 10-10 System is
______________, if it were the ratio would be
2.19x10-10 When
QgtK
QltK
QK
38
Solubility Product

• Introduction to Ksp

39
Solubility Product

• solubility-product
• the product of the solubilities
• solubility-product constant gt Ksp
• constant that is equal to the solubilities of
  the ions produced when a substance dissolves

40
Solubility Product

• In General
• AxBy ltgt xAy yB-x
• Ayx B-xy
• K ------------
• AxBy
• AxBy K Ksp Ayx B-xy

41
Solubility Product

• For silver sulfate
• Ag2SO4 (s) ltgt 2 Ag(aq) SO4-2(aq)

42
Solubility of a Precipitatein Pure Water

• EXAMPLE How many grams of AgCl (fw 143.32)
  can be dissolved in 100. mL of water at 25oC?
• AgCl ltgt Ag Cl-
• Ksp 1.82 X 10-10 (Appen. F)

43
EXAMPLE How many grams of AgCl (fw 143.32)
can be dissolved in 100. mL of water at 25oC?

• AgCl(s) Ag (aq) Cl- (aq)

Ksp AgCl- 1.82 X 10-10
x 1.35 X 10-5M
44
EXAMPLE How many grams of AgCl (fw 143.32)
can be dissolved in 100. mL of water at 25oC?
x 1.35 X 10-5M

• How many grams is that in 100 ml?

45
The Common Ion Effect