A solution of $0.1 \,M$ weak base $(B)$ is titrated with $0.1\, M$ of a strong acid $(HA)$. The variation of $pH$ of the solution with the volume of $HA$ added is shown in the figure below. What is the $p K_{ b }$ of the base? The neutralization reaction is given by $B + HA \rightarrow BH ^{+}+ A ^{-}$
Correct Answer: 3
Solution and Explanation
- From the graph, it is clear, that the equivalence point is reached at a titre value of 6 mL i.e. when 6 mL of HA are added base (B) is completely neutralized.
- So it will be half neutralized at titre value of 3 mL; when 3 mL of HA is added, ‘B’ is half – neutralized.
- So at this stage it will form a best buffer.
- So, pKb of weak base = 3
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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.