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  4. Calculate the pH of buffer solution prepared by dissolving 0.20 mol of sodium cyanate (NaCNO) and 1.0 mol of cynic acid (HCNO) in enough water to make 1.0 litre of slution. Ka(.HCNO.)=2.0× 10- 4.

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Q. Calculate the pH of buffer solution prepared by dissolving 0.20 mol of sodium cyanate (NaCNO) and 1.0 mol of cynic acid (HCNO) in enough water to make 1.0 litre of slution. $K_{a}\left(\right.HCNO\left.\right)=2.0\times 10^{- 4}.$

NTA AbhyasNTA Abhyas 2020Equilibrium

Solution:

pH $=-logK_{a}\left(\right.HCNO\left.\right)+log\frac{\left[\right. N a C N O \left]\right.}{\left[\right. H C N O \left]\right.}$

$=-\log \left(2.0 \times 10^{-4}\right)+\log \frac{0.20 \mathrm{~mol} / \mathrm{L}}{1.0 \mathrm{~mol} / \mathrm{L}}$

$=3.7+\left(\right.-0.67\left.\right)$

$=3.03\sim eq3.0$