Chemical and Ionic Equilibrium - Result Question 115

####59. 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=1.0×105)

(1997,2M)

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Solution:

  1. pH=pKIn +log10=pKIn +1

 When [In][HIn]=10

=pKIn +log(0.1)=pKIn 1 When [In][HIn]=0.1

pH range is pKIn 1 to pKIn +1.



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