Which, if any of the following mixtures will result in a precipitate. You might

Question

Which, if any of the following mixtures will result in a precipitate. You might need to know that the Ksp for AgCN is 2.2 x 10-16 and that for PbI2 is 7.9 x 10-9.

1-a mixture that is 1.2 x 10-6 M AgNO3 and 2.4 x 10-10 M NaCN

2-a mixture that is 2.3 x 10-4 M Pb(ClO4)2 and 4.6 x 10-3 M KI

answer choices:

I will precipitate but II will not precipitate

More information is required to come to a conclusion.

both will produce precipitates

Neither will produce precipitates

II will precipitate but I will not precipitate

Explanation / Answer

answer is I will precipitate but II will not precipitate

AgCN Ksp = [Ag+] [CN-] = 2.2 x 10-16

PbI2 Ksp = [Pb+2] [I-]2 = 7.9 x 10-9

We have to calculate trial Ksp values

If any solution has    trial Ksp > real Ksp then that solution will form precipitate

If   trial Ksp < Ksp then precipitate will not form.

1) a mixture that is 1.2 x 10-6 M AgNO3 and 2.4 x 10-10 M NaCN

We have to calculate trial Ksp for AgCN

Trial Ksp = [Ag+] [CN-]

[Ag+] = 1.2 x 10-6 M

[CN-] = 2.4 x 10-10 M

Trial Ksp = [Ag+] [CN-] = (1.2 x 10-6 M) x (2.4 x 10-10) = 2.88 x 10-16

Trial Ksp (2.88 x 10-16) > real Ksp (2.2 x 10-16)

So in first mixture will produce precipitate

2) a mixture that is 2.3 x 10-4 M Pb(ClO4)2 and 4.6 x 10-3 M KI

We have to calculate trial Ksp for PbI2

Trial Ksp = [Pb2+] [I-]2

[Pb+2] = 2.3 x 10-4 M

[I-] = 4.6 x 10-3 M

Trial Ksp = [Pb+2] [I-]2 = (2.3 x 10-4 M) x (4.6 x 10-3)2 = 48.688 x 10-10

Trial Ksp (48.688 x 10-10) < real Ksp (7.9 x 10-9)

So in second mixture will not produce precipitate.

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