Question

An acid-base indicator changes color between pH values of 6.0 and 8.5. Which of the following statement is true?

a. It can distinguish a pH 4 solution from a pH 5.5 solution

b. It can distinguish a pH 7.0 solution from a pH 10.5 solution

c. Solutions of pH 6 and pH 11 could have the same color.

d. Solutions of pH 5 and pH 8 could have the same color

Answer 1

b) it can distiquish a pH 7.0 solution from a 10.5 solution

Explanation

Acid base indicators having the two forms HIn and In-

these two forms are under equillibrium

HIn <-------> In- + H+

K_ind = [In-] [ H+ ]/[HIn]

So, at higher [ H+ ] , HIn- is predominent

at lower [H+] , In- is prodominent

at particular point of pH , [ HIn ] = [ In- ]

this pH is colour changing pH at which one form is start to dominate other form but for human eye , colour changing occur through range of pH

So, in the given problem

up to pH = 6 one distinct colour

between pH = 6 to pH = 8.5 , in between two colours

above pH = 8.5 other distinct colour