What is the pH of a 1M HCN solution , Ka=10^{-10}Ka=10−10?

1 Answer
VictorFiz
Jul 11, 2018

pH=5pH=5

Explanation:

HCN rightleftharpoons⇌ H^+H+ + CN^-CN−
K_aKa = [H^+H+] [CN^-CN−] //[HCN]/[HCN]=10^-1010−10

HCN
Initial_(HCN)=1MInitialHCN=1M
Delta_(HCN)=-xM
Equilibrium_(HCN)=(1-x)M

H^+
Initial_(H^+)=0M
Delta_(H^+)=+xM
Equilibrium_(H^+)=xM

CN^-
Initial_(CN^-)=0M
Delta_(CN^-)=+xM
Equilibrium_(CN^-)=xM

K_a = [x] [x] //[1-x]=10^-10**
=x^2 //1 =10^-10
Here the x value can be ignored, and therefore x becomes 0 in [1-x]

x=sqrt(10^-10)M

pH = -logx
pH = -logsqrt(10^-10)
pH=5

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