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Final Exam
Spring 2006

No electronic devices (calculators, PDAs, laptop computers, cell phones, iPods, MP3 players, etc.) are allowed for this exam.

Read all questions carefully. Numerical answers require units to obtain full credit. Answers without work shown will receive no credit. Remember to balance all chemical equations. Before beginning, carefully remove this page from the rest of the exam.

Possibly useful information:

ZeroOrder:

[A] = –kt + [A]o

FirstOrder:

SecondOrder:

ArrheniusEquation:

Kp=Kc(RT)n

R = 0.0821 L•atm/mol•K

F = 96485 coul/mol

G = wmax

G = H – TS

Go = –nFEo

pH = –log[ H3O+ ]

pOH = –log[ OH ]

pH + pOH = 14.00 (25 oC)

Kc = Ka(acid)/Ka(conj. acid)

S = RlnW

Ka×Kb = Kw

Go = –RTlnKeq

Eocell = Eored + Eoox

R = 8.314 J/mol•K

Substance

HofkJ/mole

GofkJ/mole

SoJ/mole•K

 

Acid

Ka

e

0

0

20.9

 

H2CO3

4.4×10–7

H+(aq)

0

0

0

 

HCO3

4.7×10–11

H2O(g)

–241.8

–228.6

188.7

 

H3PO4

7.1×10–3

H2O(l)

–285.8

–237.2

69.9

 

H2PO4

6.3×10–8

H2O2(l)

–187.8

–120.4

110.

 

HPO42–

4.2×10–13

H2O2(aq)

–191.2

–134.1

144.

 

H2SO3

1.3×10–2

O2(g)

0

0

205.0

 

HSO3

6.2×10–8

MnO4(aq)

–541.4

–447.2

191.2

 

HF

6.6×10–4

MnO42–(aq)

–653.0

–836.3

59.0

 

Co2+(aq)

1.3×10–9

Mn2+(aq)

–220.8

–228.1

–73.6

 

Cr3+(aq)

6.6×10–4

 

Reduction Half–reaction

Eo (V)

 

Complex ion

Kf

H2O2(aq) + 2 H+(aq) + 2 e 2 H2O(l)

1.763

 

Ag(NH3)2+

1.6×107

MnO4(aq) + 8 H+(aq) + 5 e Mn2+(aq) + 4 H2O(l)

1.51

 

Co(NH3)62+

1.3×105

O2(g) + 4 H+(aq) + 4 e 2 H2O(l)

1.229

 

Cu(NH3)42+

1.1×1013

O2(g) + 2 H+(aq) + 2 e H2O2(aq)

0.695

 

Zn(NH3)42+

4.1×108

MnO4(aq) + e MnO42–(aq)

0.56

 

 

 

 

 

 

Salt

Ksp

 

 

 

MgF2

3.7×10–8

 

 

 

BaF2

1.0×10–6


1. Complete and balance the following chemical equations.

a. aqueous nitric acid plus aqueous cesium hydroxide

b. aqueous dihydrogen phosphate ion plus aqueous carbonate ion

c. aqueous sulfite ion plus water

d. H2SO4(aq) + Al(OH)3(s)

e. Co2+(aq) + NH3(aq)

f. H2SO4(aq) + Pb(NO3)2(aq)

g. Cr3+(aq) + PO43–(aq)

h. HCN(aq) + BrO3(aq) Br2(l) + C2N2(g)

i. Mg(s) + BrO(aq) Mg(OH)2(s) + Br2(l)

j. [AuCl4](aq) + Hg(l) Hg22+(aq) + Au(s) + Cl(aq)

2. For each of the following solutions or mixtures, list all of the dissolved ions and/or molecular species (except water) in the solution. Indicate the relative concentration of each of these species as high (> 10–4 M), intermediate (between 10–4 and 10–10 M), or low (< 10–10 M). Write the reactions that are needed to answer the question. Do not do any detailed calculations.

a. 0.1 M perchloric acid

b. 0.1 M potassium hydroxide

c. 0.1 M H2SO3

d. 0.1 M Cr(NO3)3

e. 0.1 mol BaF2 placed in 1 L of water

3. The rate constants for a reaction were measured and plotted as shown below:

a. Which plot is correct to determine the activation energy? Why?

b. What is the value of the activation energy in units of kJ/mol?

c. What is the order of the reaction that was studied?

4. One of the homework assignments considered the following reaction:

MnO42–(aq) + O2(g) MnO4(aq) + H2O2(aq)

This series of questions will examine several different ways of obtaining Go.

a. Balance the reaction under acidic conditions.

b. Find the standard potential under acidic conditions.

c. Show how you would use the standard potential to calculate Go in units of kJ/mol. Do not perform the calculation.

d. Calculate Go for the reaction in units of kJ/mol using the Gibb's energies of formation.

e. Calculate Ho for the reaction in units of kJ/mol.

f. Calculate So for the reaction in units of J/mol•K.

g. Show how you would use Ho and So to calculate Go for the reaction in units of kJ/mol at 25 o. Plug the appropriate values into the appropriate equation but you do not need to calculate the final result.

h. Consider the van't Hoff plot shown below for the reaction.

The following values were extracted from the plot: slope = –4030, slope × R = –33500, slope/R = –485, intercept = 25.1, intercept × R = 209, and intercept/R = 3.02. What is the value for the enthalpy change for the reaction in units of kJ/mol? What is the value for the entropy change for the reaction in units of J/mol•K?

i. Show how you would calculate the value for the Gibb's energy change at 25 oC in units of kJ/mol using the van't Hoff plot data. Plug the appropriate values into the appropriate equation but you do not need to calculate the final result.

j. If you had done the calculations in parts c, g, and i you would have gotten –26 kJ/mol, –28.6 kJ/mol, and –28.8 kJ/mol, respectively. Compare all four values found for Go and comment on any sources of error.

k. Is the reaction spontaneous or nonspontaneous? Which thermodynamic quantity is the controlling factor in the spontaneity - the enthalpy change or the entropy change?

5. Briefly answer the following questions:

a. One of the substances listed in the Table of Solubility Product Constants is bismuthyl hydroxide, BiOOH. Describe a simple test that confirms that this substance is (BiO)(OH), not Bi(OOH).

b. A solution is prepared that has pH = 4. Is this a strong acid or a weak acid?

c. Ka for the hydrolysis of Fe3+ is about ten million times larger than Ka for the hydrolysis of Fe2+. Explain why.