SCH 204: CHEMICAL KINETICS AND ELECTROCHEMISTRY
24TH NOVEMBER
CAT 2
2014
– 5 –1
1. A substance decomposes at 600 K with a rate constant of 3.72 ×10 s .
(a) Calculate the half-life of the reaction.
(3 marks)
(b) What fraction will remain undecomposed if the substance is heated for
3 h at 600 K?
(2 marks)
+
2. The transport numbers for HCl at infinite dilution are estimated to be t =
–
–1
2
–1
0.821 and t = 0.179 and the molar conductivity is 426.16 Ω cm mol .
Calculate the mobilities of the hydrogen and chloride ions.
(3 marks)
3. The conductivity of a saturated solution of a sparingly soluble salt MX in
water at 298 K is 1.887 × 10-4 S m-1. The molar conductivity of MX at
infinite dilution at this temperature is 138.3 × 10-4 S m2 mol-1. Calculate
the solubility and solubility product of MX at this temperature. (5 marks)
–
4. The electrolytic conductivity of a 0.001 M solution of Na2SO4 is 2.6 × 10
4
–1
–1
Ω cm . If the solution is saturated with CaSO4, the conductivity
–4
–1
–1
becomes 7.0 × 10 Ω cm . Calculate the solubility product for CaSO4
using the following molar conductivities at these concentrations:
–1
2
–1
+
–1
2
–1
λ (Na ) = 50.1 Ω cm mol ; λ (1 2Ca2+) = 59.5 Ω cm mol . (3 marks)
5. Distinguish between an electrolytic cell and a voltaic cell
(2 marks)