Ionic EquilibriumHard
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)?
Options
A.0.0
B.1.0
C.2.0
D.5.0
Solution
For complete colour change, PH should change from, $P^{H} \leq \left( P^{K_{a}} + \log\frac{1}{10} \right)\text{ to }P^{H} \geq \left( P^{K_{a}} + \log 10 \right)$and hence, minimum PH change should be of 2.0 units.
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