Solution of $0.1 \,N\, NH_4OH$ and 0.1 N $NH_4Cl$ has pH 9.25. Then $pK_b$ of $NH_4OH$ :-
- 9.25
- 4.75
- 3.75
- 8.25
The Correct Option is B
Solution and Explanation
The correct option is(B): 4.75.
Solution of \(NH_4OH\) and \(NH_4Cl\) acts as a basic buffer solution. For basic buffer solution
\(pOH = PK_b + \log \frac{[salt]}{[base]}\)
\(pOH = 14 - pH\)
\(= 14 - 9.25 = 4.75\)
\(4.75 = pK_b + log \frac{0.1}{0.1}\)
\(pK_b = 4.75\)
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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.