Which is/are correct statements : (a) When 100 ml of 0.1 M NaCN solution is titrated with 0.1 M HCl

Question

Which is/are correct statements :
(a) When 100 ml of 0.1 M NaCN solution is titrated with 0.1 M HCl solution the variation of pH of solution with volume of HCl added will be (as shown in figure):
(b) Variation of degree of dissociation a with concentration for a weak electrolyte at a particular temperature is best represented by (as shown in figure) :
(c) 0.1 M acetic acid solution is titrated against 0.1 M NaOH solution. The difference in pH between 1/4 and 3/4 stages of neutralization of acid will be 2 log 3.

Accepted Answer

(a) Initially pH will decrease fast, then slowly due to buffer formation and then will decrease fast as buffer action diminishes.
(b) For a weak electrolyte
K_a =
when α << 1 then α =
as C increases ⇒ αdecreases
as C is tending to zero ⇒ α will be unity
(c) At 1/4^th neutralisation
CH₃COOH + NaOH → CH₃COONa + H₂O

pH = pK_a + log = pK_a + log
At 3/4^th neutralisation
pH = pK_a + log 3
so difference in pH = ᐃ(pH) = log 3 - log = 2 log 3

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