The pH at which an acid indicator with K_ =1 10⁻⁵ changes colour when the indicator concentration is 1 10⁻³ M is

Step-by-step solution

An acid indicator is a weak acid. It dissociates Colour A HIn H ⁺+ Colour B In ⁻ K_ In = [ H ⁺ ] [ In ⁻ ] [ HIn ] The indicator HIn will show a colour change at mid point, i.e. the point at which [ In ⁻ ]=[ HIn ] Hence, K_ in = [ H ⁺ ]=10⁻⁵ or pH =5