Chemistry
Chemistry
Problem
An acid type indicator. differs in colour from its conjugate base ( ). The human eye is sensitive to colour differences only when the ratio 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 ( )? (IIT 1997)Intuitive explanation
An acid indicator changes color when its protonation state shifts, and the human eye only detects this when the ratio of conjugate base to acid swings between extreme values. Using the Henderson–Hasselbalch equation, you can relate the pH to this ratio and find how much pH change is needed to go from one detection threshold (mostly HIn) to the other (mostly In⁻). The key is calculating the pH at each visibility limit, then finding the difference.
Intuitive explanation
An acid indicator changes color when its protonation state shifts, and the human eye only detects this when the ratio of conjugate base to acid swings between extreme values. Using the Henderson–Hasselbalch equation, you can relate the pH to this ratio and find how much pH change is needed to go from one detection threshold (mostly HIn) to the other (mostly In⁻). The key is calculating the pH at each visibility limit, then finding the difference.