Chemistry 65.100 A and V
Final Exam
April, 2001

Part A. Answer all questions (5 marks each).

  1. Define all terms in the equation DGo = DHo - TDSo. Be precise!
  2. Which of aluminum metal or nickel metal could be used to cathodically protect a piece of iron metal? How do you know? (A table of reduction potentials appears on the last page of this exam.)
  3. Reaction A is twice as fast as reaction B. What can be said about the relative values of DGo for these two reactions?
  4. For the reaction 2 NO2(g) ® N2O4(g), a plot of 1/[NO2(g)] versus time gives a straight line. What is the order of the reaction?
  5. Nitrous acid (HNO2) is a weak acid. Suggest a compound that you could add to an aqueous solution of nitrous acid to make a buffered system.
  6. Why is the boiling point of water increased when NaCl(s) is added to it?
  7. An object is thought to be billions of years old. Which radioisotope would you choose to date the object accurately: 14C (t1/2 = 5730 y) or 40K (t1/2 = 1.26 x 109 y)? Why?
  8. Name five functional groups in organic chemistry containing the carbonyl (C=O) group.

 

Part B. Answer all three questions (20 marks each).

  1. The rate constant for the reaction N2O5(g) ® 2 NO2(g) + 1/2 O2(g) is k = 4.9 x 10-3 s-1 at 338 K and 3.5 x 10-5 s-1 at 298 K.
    1. Calculate the activation energy in kJ/mol.
    2. Calculate the value of k at 360 K.
    3. Calculate the half-life of the reaction (in seconds) at 338 K.
    4. If the initial partial pressure of N2O5(g) is 0.10 atm, calculate its partial pressure after 1000 s at 338 K.

 2 (i) Complete the following nuclear reactions which have been used to produce new elements:

    (a) ? + 42He ® 24397Bk + 10n
    (b) 23892U + 126C ® ? + 6 10n
    (c) 24998Cf + 105B ® 257103Lw + ?

    (ii) The easiest fusion reaction to initiate is 21H + 31H ® 42He + 10n
    Calculate the energy released per mole of 42He produced (in kJ mol-1) given the following masses (1 amu = 1.66 x 10-27 kg):
    21H 2.01410 amu
    31H 3.01605 amu
    42He 4.00260 amu
    10n 1.00866 amu

  1. (i) Name the following compounds:

(a) (b) (c)

(d)

(ii) Draw or give correct names for the products of the following reactions:

 

(a) (b)

(c)

(d) Acetic acid + ethyl amine ®

Part C. Answer any four of the eight questions. If you answer more than four, the best four will be used to calculate your mark (20 marks each).

4. The overall reaction in the lead acid battery is:

Pb(s) + PbO2(s) + 2 H+(aq) 2 HSO4-(aq) ® 2 PbSO4(s) + 2 H2O(l)

(a) Calculate the cell potential for this battery at 25oC when [H2SO4(aq)] = 4.5 M, that is [H+(aq)] = [HSO4-(aq)] = 4.5 M.

(b) Calculate [H2SO4(aq)] when the cell potential has decreased to 1.80 V at 25oC.

5. A metallic solid with atoms in a face-centred unit cell with an edge length of 392 pm has a density of 21.45 g cm-3. Calculate the atomic mass of the metal and identify the metal.

6. Calculate the pH and the concentrations of all species in a 1.00 M aqueous solution of arsenic acid, H3AsO4. The acid dissociation constants are:

Ka1 = 6.0 x 10-3, Ka2 = 1.1 x 10-7, Ka3 = 3.0 x 10-12

7. When 1.00 g of a naturally occurring compound named reserpine is dissolved in 25.0 g of liquid camphor, the freezing point depression is 2.63 Celcius degrees. Kf for camphor is 40.0 oC kg mol-1. Calculate the molality of the solution and the molecular weight of reserpine.

8. Calculate the pressure exerted by 0.500 mol of N2 in a 1.00 L container at 25.0oC:

(a) Use the ideal gas law.
(b) Use the van der Waals equation. For N2(g), a = 1.39 atm L2 mol-2 and b = 0.0391 L mol-1.
(c) Explain the difference in the two calculated pressures.
(d) Would the difference be greater or smaller in the case of ammonia, NH3(g)? Why?

9. The normal boiling point of acetone is 56.5oC. Its enthalpy of vaporization is 32.0 kJ mol-1. At what temperature will acetone boil at an elevation of 5300 ft. where the atmospheric pressure is 630 Torr?

10. The solubility product, Ksp, for lead iodide, PbI2(s) in water is 1.4 x 10-8. Calculate the solubility of lead iodide in:
(a) water
(b) 0.10 M Pb(NO3)2(aq)
(c) 0.10 M NaI(aq)

11. The equilibrium constant for the reaction:

2 Fe+3(aq) + Hg2+2(aq) ¾ 2 Fe+2(aq) + 2 Hg+2(aq)

is Kc = 9.1 x 10-6 at 25oC.

(a) Calculate the value of DGo
(b) If the initial concentrations of each of the four species are 1.00 M, which way will the reaction proceed? (Hint - calculate the reaction quotient!)
(c) Calculate the value of DG when [Fe+3(aq)] = 0.20 M, [Hg2+2(aq)] = 0.010 M, [Fe+2(aq)] = 0.010 M and [Hg+2(aq)] = 0.025 M. In which direction will the reaction proceed to achieve equilibrium?