Answers and reasons for these two questions? 1. Recall that the first equivalenc

Question

Answers and reasons for these two questions?

1. Recall that the first equivalence point for the potentiometric titration is for the ppt of the least soluble salt while the second equivalence point for the potentiometric titration is for the most soluble salt. Keep in mind which salt precipitates at which equivalence point for a mixture of Cl- and I- titrated with Ag+. If the first equivalence point occurs at a volume of 13.65 mL and the second equivalence point occurs at a volume of 32.87 mL, what is the volume of Ag+ solution required to precipitate only chloride?

A. 13.65ml

B. 32.87ml

c. 19.22ml

D. 46.52ml

2. Calculate the cell potential when [Ag+] = 2.6 x10-8 M and a Ag/AgCl reference electrode is used.

A. 1.06V

B. 1.25V

C. 343mV

D. 153mV

Explanation / Answer

1) Since, the Ksp value of AgCl is more than that of AgI, therefore AgI precipitates first.

Thus, the volume used up in 2nd equivalence corresponds to Cl- precipitation

Hence volume required = 32.87 - 13.65 = 19.22 ml

2) AgCl(s) + e- ------>Ag(s) + Cl-(aq) ; E0cell = 0.23 V

Now, Ecell = E0cell - (0.06/n)log[Cl-]

or, Ecell = 0.23 - (0.06/1)*log[2.6*10-8]

or, Ecell = 0.685 V

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