Ionisation of weak acids and bases, Ostwald dilution law

28 questions on Ionisation of weak acids and bases, Ostwald dilution law from the Ionic Equilibrium I chapter: 6 NEET level, 11 JEE Main, 11 JEE Advanced. Each one opens with its answer and solution.

• A weak monobasic acid HA is 1% ionised in a 0.1 M solution. Taking K_a = calpha^2, the value of K_a is NEET level
• When a solution of a weak electrolyte is diluted at constant temperature, the degree of ionisation and the ionisation constant respectively NEET level
• The degree of ionisation of a weak acid in 0.1 M solution is 0.02. Assuming alpha ll 1, its degree of ionisation in 0.4 M solution at the same temperature is NEET level
• Four monobasic weak acids have the following pK_a values. Which value belongs to the strongest acid? NEET level
• The pH of a 0.01 M solution of a weak monobasic acid with K_a = 1x10^-6 is (use [H+] = sqrtK_a c) NEET level
• The percentage ionisation of a 0.01 M weak base with K_b = 1x10^-6 is (use alpha = sqrtK_b/c) NEET level
• Find the pH of 0.05 M acetic acid (K_a = 1.8x10^-5), using [H+] = sqrtK_a c. Give two decimals. JEE Main level
• A 0.2 M solution of a weak monobasic acid HA has pH 3.00. Neglecting the amount ionised compared with 0.2 M, K_a of the acid is JEE Main level
• For 0.01 M aqueous ammonia (K_b = 1.8x10^-5, 298 K), which statements are correct? (Use alpha = sqrtK_b/c.) JEE Main level
• A weak acid solution is diluted ten times at constant temperature (alpha ll 1 before and after). Its [H+] becomes JEE Main level
• A weak monobasic acid (K_a = 2.0x10^-5) is 2% ionised in solution. Using K_a = (calpha^2)/(1-alpha), find its molar concentration to three decimals. JEE Main level
• The pH of 0.1 M HCN (K_a = 2.5x10^-10; log 5 = 0.699) is JEE Main level
• A 0.25 M solution of a weak base has pH 11.0 at 298 K. Its K_b (neglect ionised fraction relative to c) is JEE Main level
• A 0.1 M solution of a weak monobasic acid has pH 2.85 (10^-2.85 = 1.413x10^-3). Using K_a = [H+]^2/(c - [H+]), find pK_a to two decimals. JEE Main level
• A weak monobasic acid HA is diluted with water at constant temperature. Which statements are correct? JEE Main level
• For ammonia pK_b = 4.75 at 298 K. The pK_a of its conjugate acid NH4+ is JEE Main level
• The degree of ionisation of 0.1 M acetic acid (K_a = 1.8x10^-5) in a solution that also contains 0.1 M HCl is yx10^-4. Find y to two decimals (assume [H+]approx... JEE Main level
• For 0.05 M of a weak monobasic acid, the molar conductivity is 7.8 S cm^2 mol^-1 and the limiting molar conductivity is 390 S cm^2 mol^-1. Taking alpha = Lambda... JEE Advanced level
• Find the pH of 0.1 M of a weak monobasic acid with K_a = 2.0x10^-4. Do not neglect the ionised amount (solve the quadratic). Give two decimals. JEE Advanced level
• A solution contains 0.1 M HA (K_a = 1x10^-5) and 0.1 M HB (K_a = 4x10^-5), both weak monobasic acids. Neglecting water ionisation and the small ionised fraction... JEE Advanced level
• A solution contains 0.1 M acetic acid (K_a = 1.8x10^-5) and 2.0x10^-3 M HCl. Taking [HA] approx 0.1 M but solving exactly for the acetate formed, i.e. K_a = x(2... JEE Advanced level
• 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 molarity c, then c is 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 7.2 = 0.857) 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 ionisation of HA in the dil... JEE Advanced level
• A 0.1 M solution of a weak acid has alpha = 0.02. It is diluted 25-fold at constant temperature. Using K_a = calpha^2, which statements are correct? 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 statements are correc... 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, which statements a... 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