Chemistry(Please check answers)
posted by Hannah on .
1) The Ka for acetic acid is 1.8e5. What is the pH of a 3.18M solution of this acid?
I did 1.8e5 = x^2/3.18
x=sqrt 1.8e5 X 3.18 = 7.56e3
pH=log(7.56e3) = 2.12
The pH is 2.12
2) At 25 degrees celsius, the pH of a 1.75M NaCN solution (the Ka for HCN is 4.0e10) is ?
4.0e10 = x^2/1.75
x=sqrt 4.0e10 X 1.75 = 2.64e5
pH=log(2.64e5) = 4.58
Did I solve these problems correctly? Thank you!

1 is right.
2 is not.
The pH of salts is determined by the hydrolysis of the salt.
CN^ + HOH ==> HCN + OH^
Kb for CN^ is (Kw/Ka for HCN) 
is Kw 1.0e14?

yes

so kb = 1.0e14 / 4.0e10 = 2.5e5

is 2.5e5 my answer or do I have to do another step?