Question

Which one of the following set of solute will form a buffer solution when dissolved in water to make 1 Litre of solution ?

• A. 0.002 mole of $HCl$
• B. 4 mole of $N{H}_3$ with 2 mole of $HCl$
• C. 2 mole of $NaCl$ with 2 mole of $HCl$
• D. 4 mole of $C{H}_{3}COOH$ with 4 mole of $NaCl$

Answer 1

The correct option is B 4 mole of $N{H}_3$ with 2 mole of $HCl$

A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or weak base and its conjugate acid.
a) $HCl$ is a strong acid so it will not form buffer solution.
b) 4 mole of $N{H}_3$ with 2 mole of $HCl$ is basic buffer because it is a mixture of weak base $\left(N{H}_3\right)$ and its salt with strong acid $\left(HCl\right)$.
c) 2 mole of $NaCl$ with 2 mole of $HCl$ is not buffer solution because it is a mixture of strong acid and salt of its conjugate base with strong base.
d) 4 mole of $C{H}_{3}COOH$ with 4 mole of $NaCl$ is not a buffer solution since it is not a mixture of weak acid and salt of its conjugate base with strong base.
Hence the correct option is b.