A 10 mL sample of 0.5 M Na 2 A is titrated with 0.5 M HCl , where H 2 A has p K a 1 = 6 and p K a 2 = 10 . Column I gives the volume of HCl added and Column II lists the possible descriptions

Question

A 10 mL sample of 0.5 M Na 2 ​ A is titrated with 0.5 M HCl , where H 2 ​ A has p K a 1 ​ = 6 and p K a 2 ​ = 10 . Column I gives the volume of HCl added and Column II lists the possible descriptions of the solution: Column I (Volume of HCl) Column II (Description) (i) 0 mL (P) buffer of HA − and A 2 − (ii) 5 mL (Q) pH = 6 (iii) 10 mL (R) pH = 8 (iv) 15 mL (S) pH < 6 (T) [ OH − ] > [ H + ] Choose the option with the correct matching:

TestHub · Accepted Answer

Na 2 ​ A = 5 mmol; HCl is 0.5 M. (i) 0 mL: only A 2 − , basic: (T). (ii) 5 mL: 2.5 mmol HCl gives 2.5 mmol HA − and 2.5 mmol A 2 − , a buffer with pH = p K a 2 ​ = 10 , basic: (P), (T). (iii) 10 mL: 5 mmol HCl turns all into HA − , pH = 2 6 + 10 ​ = 8 , basic: (R), (T). (iv) 15 mL: 7.5 mmol HCl gives 2.5 mmol H 2 ​ A and 2.5 mmol HA − , pH = p K a 1 ​ = 6 : (Q) only. Correct matching: (i)→(T); (ii)→(P,T); (iii)→(R,T); (iv)→(Q). Answer: (C).

Chemistry - Ionic Equilibrium Question with Solution | TestHub

Options:

Doubts & Discussion

Column I (Volume of HCl)	Column II (Description)
(i) 0 mL	(P) buffer of $HA^{-}$ and $A^{2 -}$
(ii) 5 mL	(Q) pH = 6
(iii) 10 mL	(R) pH = 8
(iv) 15 mL	(S) pH < 6
	(T) $[OH^{-}] > [H^{+}]$