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Ostwald Dilution Law

Calculate the...

Question

Calculate the $p H$ of a solution prepared by mixing $50.0 m L$ of $0.20 M$ $C_{2} H_{4} O_{2}$ and $50 m L$ of $0.100 M$ $N a O H$ .
$[K_{a ({C H}_{3} C O O H}) = 1.8 \times 10^{- 5}$ ]

4.44

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5

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5.74

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Solution

The correct option is A $4.44$
Given data,
$C_{2} H_{4} O_{2} = 0.2 M (50 m L)$

$N a O H = 0.1 M (50 m L)$

$K_{a} = 1.8 \times 10^{- 5}$

$p K_{a} = - log (1.8 \times 10^{- 5}) = 474$

When both acid and base reacts

$C H_{3} C O O H 10 m i l i m o l e + N a O H 5 m i l i m o l e \to C H_{3} C O O N a 5 m i l i m o l e + H_{2} O 5 m i l i m o l e$

According to Henderson - Hasselbalch equation
$p H = p K_{a} + log (\frac{C H_{3} C O O N a}{C H_{3} C O O H})$

$= 4.74 + log (\frac{5}{10})$

$= 4.74 - 0.3$

$p H = 4.44$

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