KVPY SA Exam 2011 Question Paper

Question : 71 of 80

Marks: +1, -0

CHEMISTRY

An aqueous buffer is prepared by adding 100 ml of 0.1 mol I

^{-1}

acetic acid to 50 ml of 0.2 mol l

^{-1}

of sodium acetate. If pKa of acetic acid is 4.76, the pH of the buffer is

Solution:

Meq of CH

_3

COOH = 100 × 0.1 × 1 = 10
Meq of CH

_3

COONa = 50 × 0.2 × 1 = 10

\pH=\pK_\a+\log [\CH_3\COO^{-}]/[\CH_3\COOH]

=4.76+\log 10/10

=4.76+\log 1

\pH=4.76

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