63. ANS:B THANKS! 62. Use the following data to calculate the Ksp value at 25°C

Question

63. ANS:B THANKS!

62. Use the following data to calculate the Ksp value at 25°C for PbSO4(s) EO PbOt 4H' + S042 + 2e PbSO4(s) + 2H20 PbO2 + 4H+ + 2e Pb2+ + 2H2O +1 .69 +1.46 A) 3.89 x 10105 B) 2.57×10105 C) 1.7×108 D) 5.9 x 10o E) None of these is within 5% of the correct answer ANS: C KEY: general chemistry | electrochemistry | voltaic cells | dependence of emf on concentration | Nernst equation PTS: 1 DIF: difficult TOP: 11.4 63. Calculate the solubility product of silver iodide at 25°C, given the following data AgI(s) e Ag(s) + 1 12(s) + 2e 21 Ag+ + e Ag(s) -0.15 +0.54 +0.80 A) 19 x 104 B) 8.4 x 1017 C) 3.5 x 1020 D) 2.9 x 10-3 E) 2.1 x 1012

Explanation / Answer

Ans 62

The dissociation reaction

PbSO4 = Pb(2+) + SO4(2-)

The solubility product constant expression for the reaction

Ksp=[Pb(2+)][SO4(2-)]

Write the first equation in reverse order

PbSO4 + 2H2O ==> PbO2 + 4H(+) + SO4(2-) + 2e-

This is oxidation reaction

E° ox = -1.69 V

Write the second reaction

PbO2 + 4H(+) + 2e- ==> Pb(2+) + 2H2O

This is reduction reaction

E°red = 1.46 V

Overall reaction

PbSO4 ==> Pb(2+) + SO4(2-)

E°cell= E°ox + E°red

= - 1.69 + 1.46 = -0.23 V

From the Nernst equation

E°cell = RT ln K/nF

-0.23 = (8.314 x 298 x ln K) / (2 x 96500)

ln K = (-0.23 V x 2 x 96500 ) /(8.314 x 298) = -18.1

K = 1.4 x 10^-8

The nearest answer is C

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