[Tizi]

1. Calculate the solubility of AgCN in mol/l in an aqueous buffer solution of pH 3.00!
Ksp for AgCN is 6.00*10^(-17) and Ka for HCN is 4.93*10^(-10).

Hint: the cyanide that dissolves is converted mostly to HCN on account of the fixed acidity
of the buffer. Furthermore neglect [CN-] over [HCN]!

2. After solid SrCO3 was equilibrated with an aqueous pH 8.6 buffer, the solution was found to
have [Sr2+]=1.6*10-4mol/l. From this information calculate the solubility product for SrCO3!
Ka2 for carbonic acid is 5.61*10^(-11).

Thanks a lot.
HAPPY NEW YEAR!!!

[Tizi]

ok thanks.
1) i know that in a buffer system,
   pH=pka+lg(base/acid) i.e (CN-/HCN)
   here the ka for HCN is 4.93*10^(-10), therefore pKa= 9.31
   pH=3
   3=9.31+lg(CN-/HCN)
   lg(CN-/HCN)=-6.31
   (CN-/HCN)=4.9*10^(-7)
   
   AgCN= Ag+   +   CN-
   therefore Ksp=C²
    C= square root of Ksp
    Ksp= 6.00*10^(-17)
    C=8*10^(-9)

Now I don't know how to continue, actually I don't even understand the question and how to apply the HINT provided

2)Ka2 for HCO3= 5.61*10^(-11).
   pKa2= 10.25
pH=pKa2+lg(CO3²-/HCO3)
8.6=10.25+lg(CO3²-/HCO3)
lg(CO3²-/HCO3)=-1.65
(CO3²-/HCO3)=0.0224

SrCO3=Sr²+   +   CO3²-
Ksp=[Sr2+]*[CO3²-]
Ksp=1.6*10-4mol/l*[CO3²-]
it's pretty much similar with the one above.

I am not even sure of my solution so far

[Borek]

AgCN= Ag+   +   CN-

I am not sure I understand your notation - I guess what you have on the left is meant to be AgCN solubility. However, the equation is not correct.

Can you write full mass balance for the dissolved AgCN?

[Ag⁺] = .