A 2.5 g impure sample containing weak monoacidic base (Mol. wt. = 45 u) is dissolved in 100 mL water and titrated with 0.5 M HCl. When 
of the base was neutralised, the pH was found to be 9 and at equivalence point, pH of solution is 4.5. Select correct statement(s) :
Text Solution
Verified by ExpertsCHECK THE SOLUTION.
(b,c) At 20% neutralisation, pOH = pK b + log 10 
= 5.
∴ pK b = 5 – log 
∴ K b = 2.5 × 10 –6 .
At equivalence point, pH = 
(pK w – pK b – logC)
∴ 4.5 = 
(14 – 5.6 – logC) ∴ C = 0.25 M
Now, C = 
∴ 0.25 = 
∴ V L = 0.1 L = 100 mL.
At equivalence point, n WB = n HCl
= 0.5 × 0.1 ∴ m = 2.25 g.
∴ Weight % of base in sample = 
× 100 = 90%.
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