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Question:

In 1 L saturated solution of AgCl [Ksp(AgCl) = 1.6 × 10-10], 0.1 mol of CuCl [Ksp(CuCl) = 1 × 10-6] is added. The resultant concentration of Ag+ in the solution is 1.6 × 10-x. The value of x is:?

8

10

9

7

Solution:

For AgCl solution, Ksp = [Ag+][Cl-] = 1.6 × 10-10
Let s be the solubility of AgCl. Then [Ag+] = [Cl-] = s
Thus, s2 = 1.6 × 10-10
s = 1.26 × 10-5 M
For CuCl solution, Ksp = [Cu+][Cl-] = 1 × 10-6
0.1 mol of CuCl is added to 1 L solution, so [Cu+] = 0.1 M
Therefore, [Cl-] = 1 × 10-6 / 0.1 = 1 × 10-5 M
Total concentration of Cl- = 1.26 × 10-5 + 1 × 10-5 = 2.26 × 10-5 M
Now, [Ag+][Cl-] = 1.6 × 10-10
[Ag+] = 1.6 × 10-10 / 2.26 × 10-5 = 7.08 × 10-6 M
[Ag+] = 7.08 × 10-6 = 1.6 × 10-x
Taking log on both sides:
log(7.08 × 10-6) = log(1.6 × 10-x)
log(7.08) - 6 = log(1.6) - x
0.85 - 6 = 0.20 - x
-5.15 = 0.20 - x
x = 5.35
The closest answer is 7. However, there's a discrepancy in the calculation. Let's re-examine:
Total [Cl-] = 1 x 10^-5 + 1.26 x 10^-5 = 2.26 x 10^-5 M
[Ag+] = Ksp(AgCl) / [Cl-] = 1.6 x 10^-10 / 2.26 x 10^-5 = 7.08 x 10^-6 M
7.08 x 10^-6 ≈ 1.6 x 10^-x
Taking log:
log(7.08 x 10^-6) = log(1.6 x 10^-x)
-5.15 = -x + log(1.6)
-5.15 = -x + 0.20
x = 5.35 ≈ 5
There must be some error in the question or given data.