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Basic Buffer Action

The dissociat...

Question

The dissociation constant for the weak acid $H A$ is $10^{- 5}$ . What will be the pH of an equimolar solution of $H A$ and $N a A$ ?

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Solution

$K_{a} = 10^{- 5}$

$p K_{a} = - l o g K_{a} = 5$

Equiolar concentration of $[H A]$ and $[N a A]$ means concentrations are equal.

Formula from hinderson's equation:

$p H = p K_{a} + l o g \frac{[S a l t]}{[A c i d]}$

let the concentration of Salt and acid be x molar each.

$\Rightarrow p H = 5 + l o g \frac{[S a l t]}{[A c i d]} = 5 + l o g \frac{x}{x} = 5 + 0 = 5$

$p H = 5$

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