JEE Main Chemistry question
An acid type indicator HIn differs in colour from its conjugate base (In⁻). The human eye is sensitive to colour differences only when the ratio [In⁻]/[HIn] is greater than 10 or smaller than 0.1. What should be the minimum change in the pH of the solution to observe a complete colour change (Ka=1.0×10⁻⁵)?
Answer: (B)
Solution
Full colour change spans pKa±1 (ratio 0.1 to 10), a total of 2 pH units.