Ksp question?

Question

M+ is added to a solution of 0.0038 M X- and 0.0011 M Z-. MX has Ksp=9.4E-9, while MZ has Ksp=2.4E-10. What percentage of the Z- is still in solution (not precipitated) when the MX just starts to precipitate? Answer in units of %.

Answer 1

when the MX just starts to precipitate

K = [M+] [X-]

9,4 × 10−9 = [M+] [0.0038]

when MX is ready to ppt, [M+] = 2.47e-6 molar

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question is, What amount of the Z− is in solution when [M+] = 2.47e-6 molar ?

K = [M+] [Z-]

2.4 × 10−10 = [M+] [Z-]

2.4 × 10−10 = [2.47e-6] [Z-]

[Z-] = 9.7e-5 molar

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What percentage

of the Z− is still in solution ?

9.7e-5molar / 0.0011 molar @ start times 100 = 8.8%

your answer: 8.8%