The initial concentration of HF solution used is | TestHub

Passage / Comprehension

In water, HF behaves as a weak acid. The reactions involved are:

Reaction-I: $H F (a q) + H_{2} O (l) ⇌ H_{3} O^{+} (a q) + F^{-} (a q)$ ; $K_{1} = 1.1 \times 1 0^{- 3}$

Reaction-II: $H F (a q) + F^{-} (a q) ⇌ H F_{2}^{-} (a q)$ ; $K_{2} = 0.26$

Two chemists wanted to determine the acidity constant, $K_{1}$ , using the same HF solution and measuring the pH of the solution. One chemist was having the idea of reaction-I only while the other chemist was having the idea of both reactions. Surprisingly, both the chemist determined the same value of K₁ (as given above).

The initial concentration of HF solution used is

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Answer:

Solution:

For the same $K_{1}$ from pH (ignoring reaction-II), take $[H_{3} O^{+}] = K_{1}$ ; then from $K_{1} = \frac{[ H _{3} O ^{+} ] ^{2}}{[ H F ] _{0}}$ $\Rightarrow$ $[H F]_{0} = K_{1} = 1.1 \times 1 0^{- 3} M$ ; considering $F^{-}$ consumption via $H F + F^{-} ⇌ H F_{2}^{-}$ gives $[H F]_{0} = 2 K_{1} = 2.2 \times 1 0^{- 3} M$ .

Chemistry - Ionic Equilibrium Question with Solution | TestHub

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