Question

If ka of hcn is 4*10^-10 then the ph of 0.25 molar hcn is?

Answer 1

If pKa =4, Ka = 1E-4

As it's a weak acid we can assume that the concentration of hydrogen ions equals the concentration of cyanide ions.

So using the Ka expression for HCN, the concentration of hydrogen ions = √(0.01 × 1E-4) = 0.001 mol/dm³

Hence pH = -log(0.001) = 3