Redox equilibrium

2011-02-18 5:13 pm

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Q1: At 298K, the reduction potential , E, of Ag+(aq)|Ag(s) can be obtained from the equation: E = EΦ + 0.059 log[Ag+(aq)] The e.m.f. of the cell was found to be 0.17V at 298K. Calculate the concentration of silver ions in the saturated AgCl(aq)(Given : EΦ of Ag+(aq)|Ag(s) = +0.80V at 298K) Q2: State, with explanation, the effect on the cell e.m.f. of adding a small volume of KCl(aq) to the saturated AgCl(aq). Please give the answer with detailed steps, thx!

回答 (1)

pingshek

2011-02-19 7:07 am

✔ 最佳答案

1)
Let y M be the [Ag⁺] in the sat. AgCl solution.
y < 0.01 M

For the 0.01 M AgNO3 solution: E1 = E°+ 0.059 x log(0.01) ... [1]
For the sat. AgNO3 solution: E2 = E° + 0.059 x logy ... [2]

[1] - [2]:
Ecell = 0.059 x {log(0.01) - logy}
0.059 x (-2 - logy) = 0.17
-2 - logy = 0.17/0.059
logy = -2 - (0.17/0.059)
y = 1.31 x 10^-5

[Ag⁺] in the sat. AgCl solution = 1.31 x 10^-5 M

2)
AgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq)

When the small volume of KCl solution is added, the concentration of Cl⁻ ions increases. This will shift the equilibrium position of the left, and thus the solubility of AgCl decreases. This is known as common ion effect.

參考: miraco

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