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  • The pKa of a weak acid (HA) is 4.5. The pOH of an aqueous buffer solution of HA in which 50% of the acid is ionized is:Option: 1 2.5</

The pKa of a weak acid (HA) is 4.5. The pOH of an aqueous buffer solution of HA in which 50% of the acid is ionized is:

Option: 1

2.5


Option: 2

5.9


Option: 3

9.5


Option: 4

6


Answers (1)

best_answer

Let us consider the dissociation equilibrium of the acid \mathrm{HA}

\mathrm{HA \rightleftharpoons H^+ + A^-}

Writing the expression for the equilibrium constant

\mathrm{k_a = \frac{[H^+][A^-]}{[HA]}}

When the acid is 50% dissociated, \mathrm{\left [ A^{-} \right ]=\left [ HA \right ]}

\mathrm{\therefore [H^+]=k_a \Rightarrow pH= pk_a}

\mathrm{Given\; \; pK_{a}=4.5\; \; \therefore pH=4.5}

\mathrm{\therefore \; \; pOH=14-4.5=9.5}

Hence, the correct answer is Option (3)

Posted by

SANGALDEEP SINGH

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