Addition of sodium hydroxide solution to a weak acid (HA) results in a buffer of pH 6. If ionisation constant of HA is `10^(-5)`, the ratio of salt to acid concentration in the buffer solution will be :

Options

A. `4:5`
B. `1:10`
C. `10:1`
D. `5:4`

Answer

C

Explanation

`HAhArrH^(+)+A^(-)`
(Unionized, weak acid and common ion effect)
`HA+NaOHtoNaA+H_(2)O`
`NaAtoNa^(+)+A^(-)` (ionized)
`K_(a)=([H^(+)][A^(-)])/([HA])`
Given, pH =6, `[H^(+)]=1xx10^(-6)`
`[H^(+)]=(K_(a)["Acid"])/(["Salt"])`
`(["Acid"])/(["Salt"])=(K_(a))/([H^(+)])=(10^(-5))/(10^(-6))=10:1`