Question

An acidic buffer is obtained on mixing

• A. $100mL$ of $0.1M$ $\mathrm{HCl}$ and $200mL$ of $0.1M$ ${\mathrm{CH}}_3\mathrm{COONa}$
• B. $100mL$ of $0.1M$ $\mathrm{HCl}$ and $200mL$ of $0.1M$ $\mathrm{NaCl}$
• C. $100mL$ of $0.1M$ ${\mathrm{CH}}_3\mathrm{COOH}$ and $100mL$ of $0.1M$$\mathrm{NaOH}$
• D. $100mL$ of $0.1M$ ${\mathrm{CH}}_3\mathrm{COOH}$ and $200mL$ of $0.1M$ $\mathrm{NaOH}$

Answer 1

The correct option is A

$100mL$ of $0.1M$ $\mathrm{HCl}$ and $200mL$ of $0.1M$ ${\mathrm{CH}}_3\mathrm{COONa}$

Explanation for correct option:

(A) $\mathbf{100}\mathbf{}\mathit{m}\mathit{L}$ of $\mathbf{0}\mathbf{.}\mathbf{1}\mathbf{}\mathit{M}$ $\mathbf{HCl}$ and $\mathbf{200}\mathbf{}\mathit{m}\mathit{L}$ of $\mathbf{0}\mathbf{.}\mathbf{1}\mathbf{}\mathit{M}$ ${\mathbf{CH}}_{\mathbf{3}}\mathbf{COONa}$

1. Acidic buffer are solutions which has acidic pH and is prepared by mixing a weak acid and its salt with a strong base.
2. The reaction of $\mathrm{HCl}$ and ${\mathrm{CH}}_3\mathrm{COONa}$ is: $\mathrm{HCl}+{\mathrm{CH}}_3\mathrm{COONa}\to {\mathrm{CH}}_3\mathrm{COOH}+\mathrm{NaCl}$
3. In this reaction, weak acid is ${\mathrm{CH}}_3\mathrm{COOH}$ and a salt with strong base is ${\mathrm{CH}}_3\mathrm{COONa}$.
4. Hence this mixture is an acidic buffer.

Explanation for incorrect option:

(B) $\mathbf{100}\mathbf{}\mathit{m}\mathit{L}$ of $\mathbf{0}\mathbf{.}\mathbf{1}\mathbf{}\mathit{M}$ $\mathbf{HCl}$ and $\mathbf{200}\mathbf{}\mathit{m}\mathit{L}$ of $\mathbf{0}\mathbf{.}\mathbf{1}\mathbf{}\mathit{M}$ $\mathbf{NaCl}$

1. The mixture of $\mathrm{HCl}$ and $\mathrm{NaCl}$ does not prepare an acidic buffer.
2. As $\mathrm{HCl}$ is strong acid and $\mathrm{NaCl}$ is a neutral salt it does not result in formation of weak acid and its salt with a strong base.

(C) $\mathbf{100}\mathbf{}\mathit{m}\mathit{L}$ of $\mathbf{0}\mathbf{.}\mathbf{1}\mathbf{}\mathit{M}$ ${\mathbf{CH}}_{\mathbf{3}}\mathbf{COOH}$ and $\mathbf{100}\mathbf{}\mathit{m}\mathit{L}$ of $\mathbf{0}\mathbf{.}\mathbf{1}\mathbf{}\mathit{M}$$\mathbf{NaOH}$

1. The mixture of ${\mathrm{CH}}_3\mathrm{COOH}$ and $\mathrm{NaOH}$ does not prepare an acidic buffer.
2. As ${\mathrm{CH}}_3\mathrm{COOH}$ is weak acid and $\mathrm{NaOH}$ is strong base it does not result in formation of weak acid and its salt with a strong base.

(D) $\mathbf{100}\mathbf{}\mathit{m}\mathit{L}$ of $\mathbf{0}\mathbf{.}\mathbf{1}\mathbf{}\mathit{M}$ ${\mathbf{CH}}_{\mathbf{3}}\mathbf{COOH}$ and $\mathbf{200}\mathbf{}\mathit{m}\mathit{L}$ of $\mathbf{0}\mathbf{.}\mathbf{1}\mathbf{}\mathit{M}$ $\mathbf{NaOH}$

1. The mixture of ${\mathrm{CH}}_3\mathrm{COOH}$ and $\mathrm{NaOH}$ does not prepare an acidic buffer.
2. As ${\mathrm{CH}}_3\mathrm{COOH}$ is weak acid and $\mathrm{NaOH}$ is strong base it does not result in formation of weak acid and its salt with a strong base.

Hence option A is correct, acidic buffer is obtained by mixing $100mL$ of $0.1M$ $\mathrm{HCl}$ and $200mL$ of $0.1M$ ${\mathrm{CH}}_3\mathrm{COONa}$.