Class XII students were asked to prepare one litre of buffer solution of pH \(8.26\) by their Chemistry teacher. The amount of ammonium chloride to be dissolved by the student in \(0.2\) M ammonia solution to make one litre of the buffer is (Given : \(pK_b\) \((NH_3)\) = \(4.74\), Molar mass of \(NH_3\) = \(17\) g \(mol^{–1}\), Molar mass of \(NH_4Cl\) = \(53.5\) \(g\) \(mol^{–1}\))
- 53.5 g
- 72.3 g
- 107.0 g
- 126.0 g
The Correct Option is C
Solution and Explanation
For basic Buffer,
\(pOH=pK_b+log\frac{[salt]}{[Base]}\)
\(pOH=14–8.26=5.74\)
\(5.74=4.74+log\frac{[NH_4Cl]}{0.2}\)
\([NH_4Cl]=2 M\)
Moles of \( NH_4Cl = 2 × 1 = 2 \) \(moles\)
Weight of \(NH_4Cl\) = \(2 × 53.5 = 107\) \(g\)
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Concepts Used:
Buffer solutions
The buffer solution is a solution that is able to maintain its Hydrogen ion concentration (pH) with only minor changes on the dilution or addition of a small amount of either acid or base. They are used in fermentation, food preservatives, drug delivery, printing, the activity of enzymes and many more.
Buffer solutions are aqueous solutions containing a weak acid and its salt - acid buffer or a weak base and its salt - base buffer.
Types of Buffer Solution
Acidic Buffers
These solutions are used to maintain acidic environments. Also, it has acidic pH and is prepared by mixing a weak acid and its salt with a strong base. An aqueous solution of an equal concentration of acetic acid and sodium acetate has a pH of 4.74.
Alkaline Buffers
These solutions are used to maintain basic conditions. It has a basic pH and is prepared by mixing a weak base and its salt with strong acid. The aqueous solution of an equal concentration of ammonium hydroxide and ammonium chloride has a pH of 9.25.