Chemical and Ionic Equilibrium - Result Question 128

####71. How many gram-mole of HCl will be required to prepare one litre of buffer solution (containing NaCN and HCl ) of pH8.5 using 0.01g formula weight of NaCN ?

KHCN=4.1×1010

(1988,4M)

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Solution:

  1. HCN for buffer will be formed by the reaction

NaCN+HClNaCl+HCN

mmol of NaCN present initially =0.0149×1000=0.2

Let xmmol of HCl is added so that xmmol of NaCN will be neutralised forming x mmol of HCN.

$$ \begin{aligned} pH & =p K _a+\log \frac{[NaCN]}{[HCN]} \



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