Question

Electrochemistry

1.Consider the Daniel Cell at the indicated molalities:

Zn(s)|ZnSO₄(aq, 0.100 M)||CuSO₄(aq, 0.500 M)|Cu(s)

a) Calculate the ionic strength I and mean activity coefficient   (gamma+-) for each species, the latter using the Debye - Hückel limiting law, and compare this value to those found in

the data tables (i.e.,   (gamma +-),ZnSO₄ = 0.150 at 0.100 M;   (gamma +-),CuSO₄ = 0.0620 at 0.500 M).

b) Calculate E using the molalities indicated in the above Cell and the mean activity coefficients from the data tables. What is the relative error if only the concentrations are used?

(You can skip no. 1 as I got the answer for it, elsewhere.)

2. The Edison storage cell is described by,
Fe(s)|FeO(s)|KOH(aq, a)|Ni₂O₃(s)|NiO(s)|Ni(s)

The half-cell reactions are as follows,
Ni₂O₃(s) +H₂O(l) + 2e– ----> 2NiO(s) + 2OH–(aq. ) Eo = 0.40 V

FeO(s) + H2=₂O(l) + 2e– -----> Fe(s) + 2OH–(aq) Eo = –0.87 V

a) What is the overall cell reaction?

b) How does the cell potential depend on the activity of KOH?

c)How much work can be obtained per pound (453.6 g) of the active materials in the cell?

3) Graph the radius of the ionic cloud as a function of ionic strength of a sodium ion dissolved in ethanol at 298.15 K for a concentration of NaCl from 0.001 to 0.010 M at 0.0001 intervals in ethanol; for ethanol, epsilon r = 25.3 and rho s = 789 kg m^-3. Note: remember to include a  sample calculation for both I and k^-1 as well as a copy of the spreadsheet and final graph.

Kinetics

4. The gas phase reaction 2 N₂O₅(g) ⟶ 4 NO₂(g) + O₂(g) obeys first order kinetics. The half- life for the reaction is 8.95×104 s at 0.0 oC and the half-life for the reaction is 795 s at 50.0 oC.

a) Evaluate the Arrhenius parameters Ea and A.

b) Calculate the rate constant at 25.0 oC.

5) Bananas are somewhat radioactive due to the presence of substantial amounts of potassium. The isotope of potassium is radioactive and decays by the two different pathways shown below:

  ⁴⁰₁₉K --(k1)--> ⁴⁰₂₀ Ca +beta^-  (an antineutrino) (89.3%)

⁴⁰₁₉K  ⎯⎯(k2)--> ⁴⁰₁₈ Ar +gamma+ beta (a gamma ray and a neutrino) (10.7%)

The half-life for potassium decay is 1.251×10⁹ years. Evaluate the rate constants k1 and k2.

Answer 1