An acid type indicator, H In differs in colour from its conjugate base `(In^(-))` . The human eye is sensitive to colour differences only when the ratio `[In^(-)]//[H In]` is greater than 10 or smaller than `0.1`. What should to observe a complete colour change ? `(K_(a)= 1.0xx10^(-5))`

Explanation

`HIn hArr H^(+) + In^(-)`
`K_a =([H^+][In^-])/"[Hi n]"` or `[H^+]=K_a([HI n])/([In^-])`
When `([In^-])/([Hi n])=10, [H^+]=10^(-5)xx1/10=10^(-6)`
or pH=-log `[H^+]=-log (10^(-6))` =6
When `([In^-])/([Hi n])=0.1 , [H^+]=10^(-5)xx10=10^(-4)`
or pH=-log `[H^+]=-log (10^(-4))` =4
`therefore` Minimum pH change =2