Find the pH at which an acid indicator having concentration `1.0xx10^(-4)M`, having dissociation of `1%` shows a colour change.

Answer

8

Explanation

`H InhArrH^(+)+In^(-)`
`[H^(+)]=c.alpha=1.0xx10^(-4)xx0.01=1.0xx10^(-6)`
`K_(a)=c.alpha.alpha=1.0xx10^(-6)xx0.01=1.0xx10^(-8)`
Now, the indicator will show colour when `[In^(-)]=[H In]`
`:. K_(a)=[H^(+)])`
or `[H^(+)]=K_(a)=1.0xx10^(-8)`
or `pH=8`