The ionisation constant of chloroacetic acid is `1.35xx10^(-3)`. What will be the pH of 0.1 M acid and its 0.1 M sodium salt solution?

Explanation

`pK_(a)=-log_(10)K_(a)=-log_(10)(1.35xx10^(-3))=2.87`
For the solution of a monoprotic acid,
`pH=(1)/(2)pK_(a)-(1)/(2)logc`
Given: `c=0.1(M)`
`therefore pH=(1)/(2)xx2.87-(1)/(2)log0.1=1.935`
For the solution of sodium salt of chloroacetic acid, which is a salt of strong base and weak acid,
`pH=7+(1)/(2)+(1)/(2)pK_(a)+(1)/(2)logc`
Given: `c=01M`
`therefore pH=7+(1)/(2)xx2.87+(1)/(2)log0.1=7.93`.