A $0.1 M$ solution of a weak acid has $α = 0.02$ . It is diluted $25$ -fold at constant temperature. Using $K_{a} = c α^{2}$ , which statements are correct?

Answer: A, B, D

K_{a} = 0.1 \times (0.02)^{2} = 4.0 \times 1 0^{- 5}

is unchanged on dilution. New

c = 0.004 M

α = K_{a} / c = 0.10

[H X^{+}] = c α = 4.0 \times 1 0^{- 4} M

(down from

2.0 \times 1 0^{- 3}

), a fall by factor

5

, so pH rises by

lo g 5 = 0.70

HX has K_a = 4x10^-5 and HY has K_a = 1x10^-6 (both weak, alpha ll 1). If 0.1 M HX has the same degree of ionisation as HY solution of molar... JEE Advanced level
A solution contains 0.20 M NH3 (K_b = 1.8x10^-5) and 0.05 M NH4Cl (fully ionised); the ionisation of NH3 is small. Its pH at 298 K is (log 7... JEE Advanced level
10 mL of 0.1 M HA (K_a = 1.0x10^-5) is diluted to 1.0 L. Using K_a = (calpha^2)/(1-alpha) (do not assume alpha ll 1), the percentage ionisat... JEE Advanced level
Weak monobasic acids HA (pK_a = 4.0) and HB (pK_a = 6.0) are each present as 0.1 M solutions (separately) at 298 K, with alpha ll 1. Which s... JEE Advanced level
0.20 M HA (K_a = 4.0x10^-5) is made 0.10 M in NaA by dissolving the solid (no volume change). Taking [HA] approx 0.20 and [A-] approx 0.10 M... JEE Advanced level
For 0.05 M NH3 (K_b = 1.8x10^-5, 298 K; log 9.487 = 0.977) with alpha ll 1, which statements are correct? JEE Advanced level