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Acidic Buffer Action

A 30 mL solut...

Question

A $30 m L$ solution of $0.2 M N H_{4} O H$ is titrated with $0.2 M H C l$ . Find the $p H$ of the solution when $10 m L$ of $H C l$ has been added.
Given $p K_{b} (N H_{4} O H) = 4.74$

4.44

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9.56

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5.44

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8.56

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Solution

The correct option is B 9.56
mmol of $N H_{4} O H = 30 \times 0.2 = 6$
mmol of $H C l = 10 \times 0.2 = 2$

$N H_{4} O H (a q) + H C l (a q) \to N H_{4} C l (a q) + H_{2} O (l) I n i t i a l : 6200 F i n a l : 4022$

After titration, $N H_{4} C l$ and $N H_{4} O H$ is there which constitutes a basic buffer.
$Final concentration = \frac{Moles}{Total Volume}$
Total Volume $= 30 + 10 = 40 m L$
$[N H_{4} O H]_{f i n a l} = \frac{4}{40} M$
$[N H_{4} C l]_{f i n a l} = [N H_{4}^{+}]_{f i n a l} = \frac{2}{40} M$
For a basic buffer,
$p O H = p K_{b} + l o g (\frac{[N H_{4}^{+}]}{[N H_{4} O H]}) p O H = 4.74 + l o g ⎛ ⎝ \frac{\frac{2}{40}}{\frac{4}{40}} ⎞ ⎠ p O H = 4.74 + l o g (\frac{1}{2}) = 4.74 - 0.3 p O H = 4.44 p H = 14 - 4.44 = 9.56$

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Acidic Buffer Action

Standard XII Chemistry

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A 30 mL solution of 0.2 M NH4OH is titrated with 0.2 M HCl. Find the pH of the solution when 10 mL of HCl has been added. Given pKb(NH4OH)=4.74

A $30 m L$ solution of $0.2 M N H_{4} O H$ is titrated with $0.2 M H C l$ . Find the $p H$ of the solution when $10 m L$ of $H C l$ has been added.
Given $p K_{b} (N H_{4} O H) = 4.74$