1. Tardigrade
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  3. Chemistry
  4. The dissociation constant of a weak acid is 1 × 10-4 in order to prepare a buffer solution with a pH = 5 the [salt] / [Acid] ratio should be :

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Q. The dissociation constant of a weak acid is $1 \times 10^{-4}$ in order to prepare a buffer solution with a $pH = 5$ the [salt] / [Acid] ratio should be :

NEETNEET 2013Equilibrium

Solution:

$\begin{array}{l} pH = p K_{a}+\log \frac{[ Salt ]}{[ Acid ]} \\ 5=-\log K_{a}+\log \frac{[ Salt ]}{[ Acid ]} \quad\left[\because p K_{a}=-\log K_{a}\right] \\ 5=-\log \left[1 \times 10^{-4}\right]+\log \frac{[ Salt ]}{[ Acid ]} \\ 5=4+\log \frac{[ Salt ]}{[ Acid ]} \\ 5-4=\log \frac{\text { [Salt] }}{[ Acid ]} \\ 1=\log \frac{[ Salt ]}{[ Acid ]} \\ \frac{[ Salt ]}{[ Acid ]}=10 \text { i.e., } 10: 1 \end{array}$