Posted by Linda on .
Ignoring activities, determine the molar solubility (S) of Zn(CN)2 in a solution with a pH = 3.63. Ksp (Zn(CN)2) = 3.0 × 10-16; Ka (HCN) = 6.2 × 10-10.
I'm completely lost help please!
You can work this one of two ways. Here is one way; I don't know which would be easier for you to understand.
Zn(CN)2 ==> Zn + 2CN^-
Then 2CN^- + 2H^+ ==> 2HCN.
Solubility Zn(CN)2 = S
Then Zn^2+ = S and
CN^- = 2S. The total CN = 2S and
2S = (CN^-) + (HCN)
Use Ka for HCN = (H^+)(CN^-)/(HCN)
Solve for (HCN)/(CN^-) = and convert that to (HCN) = (CN^-)*some number.
Then go back to 2S = CN + HCN
and this becomes 2S = CN + somenumber*CN
and convert this to CN = ? in terms of S.
Plug this back into Ksp and solve for S. I get a value of 0.022 M. Try this and see if you understand. If so there is no need to go through the other method.
this doesn't make sense