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Final Exam
Spring 2004


Possibly useful information:

Similar formulas for So and Go

Go = Ho – TSo

Kw = KaKb
(for conjugate acid-base pairs)

Kc = Ka/Ka(conjugate acid)

Go = –RTlnKeq

pH = –log[H3O+]

Go = wmax

S = RlnW

R = 8.314 J/mol•K = 0.0821 L•atm/mol•K

Complex Ion

Kf (25 oC)

Salt

Ksp (25 oC)

Ag(NH3)2+

1.6×107

Al(OH)3

1.1×10–33

Al(OH)4

1.1×1033

Ca(OH)2

2.5×10–14

Cr(OH)4

8×1029

Cr(OH)3

6.3×10–31

Zn(NH3)42+

4.1×108

Mg(OH)2

1.8×10–11

 

Substance

Go (kJ/mol, 25 oC)

Acid

Ka (pKa) (25 oC)

H2O(g)

–228.6

Al3+(aq)

1.4×10–5 (4.85)

H2O(l)

–237.2

CH3NH3+(aq)

2.4×10–11 (10.62)

H3O+(aq)

–237.2

Co2+(aq)

1.3×10–9 (8.89)

Co2+(aq)

–51.5

Cr3+(aq)

6.1×10–4 (3.21)

Mg2+(aq)

–454.8

HF(aq)

6.6×10–4 (3.18)

MgOH+(aq)

–626.7

HONH3+(aq)

1.1×10–6 (5.96)

Co(OH)2(s)

–454.5

HSO4(aq)

1.1×10–2 (1.96)

Mg(OH)2(s)

–833.9

Zn2+(aq)

2.5×10–10 (9.60)

 

Half–reaction

Eored (V, 25 oC)

Ag+(aq) + e Ag(s)

0.800

AgCl(s) + e Ag(s) + Cl(aq)

0.222

Co2+(aq) + 2 e Co(s)

–0.277

Zn2+(aq) + 2 e Zn(s)

–0.763


1. Complete and balance the following reactions:

a. H2SO4(aq) + NaOH(aq)

b. Pb(NO3)2(aq) + NaCl(aq)

c. Zn2+(aq) + NH3(aq)

d. C6H5NH2(aq) + H2O(l)

e. Cr3+(aq) + H2O(l)

f. NiCl2(aq) + K3PO4(aq)

g. HF(aq) + CH3NH2(aq)

h. Fe(NO3)2(aq) + KCl(aq)

i. VO2+(aq) + S(s)VO2+(aq) + H2SO3(aq)

j. [Cr(OH)4](aq) + ClO3(aq) CrO42–(aq) + Cl(aq)

2. Consider the following reaction:

HgCl2(aq) + C2O42–(aq) Cl(aq) + CO2(g) + Hg2Cl2(s)

a. Balance the reaction.

b. The following rate data was collected:

Experiment
[HgCl2], M
[C2O42–], M
Initial rate, mol L–1 min–1
1
2
3
4
0.105
0.105
0.052
0.052
0.15
0.30
0.30
0.15
1.8×10–5
7.1×10–5
3.5×10–5
8.9×10–6

Determine the order of reaction with respect to HgCl2, with respect to C2O42–, and the overall order.

c. Write the rate law for the reaction.

3. Al(OH)3 is a sparingly soluble salt. Determine if the solubility will increase, decrease, or stay the same in the following solutions. Briefly (15 words or less) explain your answer.

a. 1 M HCl solution.

b. 1 M NaClO4 solution.

c. 1 M NH3 solution.

d. 1 M NaOH solution.

4. You need to prepare a buffer with pH = 6.00 and a buffer capacity of about 0.1 M.

a. Based on information provided with this exam, which substances should you use to prepare the buffer?

b. 0.010 mol of NaOH is added to 1.0 L of your buffer; estimate the new pH.

c. 1.00 mol of NaOH is added to 1.0 L of your buffer; estimate the new pH.

5. An assumption that we make about the group 2 hydroxides is that both hydroxides completely dissociate. This question will test that assumption using magnesium hydroxide as an example.

a. Write the hydrolysis reaction for the magnesium ion.

b. Find Go for the reaction in part a.

c. Show how you would find the equilibrium constant at 25 oC for the reaction in part a using data available on this exam. Do not do the calculation, but show the set up and plug in numbers into whatever equations are required. Be sure that all values are in the correct units.

d. What subscript should be used with the equilibrium constant found in part c?

e. The calculation from part c gives an equilibrium constant of ~10–12. Estimate the pH and per cent ionization of a 1 M solution of magnesium ion.

f. The per cent dissociation of the second hydroxide in magnesium hydroxide is equal to 100 – (per cent ionization of magnesium ion). Based on the result in part e, is it justifiable to assume that both hydroxides should be considered strong? Why or why not?

6. This question will use available data to fill in a value in the Table of Thermodynamic Quantities.

a. Write the hydrolysis reaction for Co2+(aq).

b. Show how you would find Go at 25 oC for the reaction in part a using data available on this exam. Do not do the calculation, but show the set up and plug in numbers into whatever equations are required. Be sure that all values are in the correct units.

c. The answer for part b is –50.7 kJ. Use this value to find Gfo for the cobalt(II) monohydroxide cation.

d. A common mistake beginning students make is to write the hydrolysis reaction for Co2+(aq) to give cobalt(II) hydroxide. Find Go for this hypothetical reaction and explain why the reaction does not occur.

7. Consider the cell:

Co(s)|Co2+(aq) pH = 0 ||AgCl(s)|Cl(aq)| pH = 0 |Ag(s)

a. Write the oxidation half–reaction.

b. Write the reduction half–reaction.

c. Write the net reaction.

d. Find the cell potential under standard conditions.

e. Is the reaction spontaneous or nonspontaneous? Why?

f. Write the mass action expression for the net reaction that would be used in the Nernst equation.

g. Will the spontaneity increase or decrease if the concentration of chloride ion is increased in the cell? Why?