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NTA Abhyas JEE Main2020ChemistryIonic EquilibriumPractice

An acid base indicator has K a = 3 × 1 0 - 5 . The acid form of the indicator is red and the basic form is blue. By how much must the pH change in order to change the indicator from 75% red to 75% blue (log 3 = 0.4770)

Options

  1. A0.95
  2. B2.3
  3. C0.75
  4. D5

Correct answer

A. 0.95

Step-by-step solution

pH change = pH of 75 % blue - pH of 75% red = p K a + l o g l o g 75 25 - p K a + l o g l o g 25 75 = l o g 3 + l o g 3 p H = 0.954

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