PYQ Vault
EbooksTutor

pH of a weak acid or weak base from Ka or Kb and concentration (or Kb from pH)

This type of question, asked 4 times: 28 Jul 2022, 23 Jan 2025, 28 Jan 2026 S1, 2 Apr 2026 S2. All 4 questions below, oldest first.

Try each one first, then open its answer.

  1. Question 1

    28 Jul 2022

    55
    KaK_{a} for butyric acid (C3H7COOH)\left( C_{3}H_{7}COOH \right) is 2×10−52 \times10^{- 5}. The pHpH of 0.2M0.2M solution of butyric acid is ____\_\_\_\_ ×10−1\times10^{- 1}. (Nearest integer) [Given log⁡2=0.30\log2 = 0.30 ]

  2. Question 2

    23 Jan 2025

    46
    If 1 mM solution of ethylamine produces pH=9pH = 9, then the ionization constant (Kb)\left( K_{b} \right) of ethylamine is 10−x10^{- x}. The value of xx is _____\_\_\_\_\_ (nearest integer). [The degree of ionization of ethylamine can be neglected with respect to unity.]

  3. Question 3

    28 Jan 2026 S1

    50
    Consider the dissociation equilibrium of the following weak acid HA⇌H+(aq)+A−(aq)HA \rightleftharpoons H^{+}(aq) + A^{-}(aq) If the pKa of the acid is 4 , then the pH of 10 mM HA solution is ____\_\_\_\_ . (Nearest integer) [Given : The degree of dissociation can be neglected with respect to unity]

  4. Question 4

    2 Apr 2026 S2

    31
    At 25∘C,20.0 mL25^{\circ}C,20.0\text{ }mL of 0.2 M weak monoprotic acid HX is titrated against 0.2 M NaOH . The pH of the solution (a) at the start of the titration (when NaOH has not been added) and (b) when 10 mL of NaOH is added respectively, are : Given : Ka=5×10−4,pKa=3.3,α≪1K_{a}= 5 \times10^{- 4},pK_{a}= 3.3,\alpha\ll 1

    Tap an option to check your answer.