Polyprotic acids and amphiprotic species

36 questions on Polyprotic acids and amphiprotic species from the Ionic Equilibrium II chapter: 8 NEET level, 14 JEE Main, 14 JEE Advanced. Each one opens with its answer and solution.

• The conjugate base of H2PO4- is NEET level
• Which of the following species is amphiprotic? NEET level
• In an aqueous solution of phosphoric acid (K_a1 = 7.5x10^-3, K_a2 = 6.2x10^-8, K_a3 = 4.8x10^-13), the species present in the smallest concentration is NEET level
• The pH of an aqueous solution of sodium hydrogencarbonate is approximately tfrac12(pK_a1 + pK_a2). For H2CO3, pK_a1 = 6.35 and pK_a2 = 10.33. The pH is about NEET level
• A solution is 0.10 M in H2S and 0.20 M in HCl (so [H+] = 0.20 M). For H2S, K_a1 = 1.0x10^-7 and K_a2 = 1.2x10^-13. Taking [H2S] = 0.10 M, the concentration of S... JEE Main level
• Find the pH of 0.020 M carbonic acid at 298 K, taking K_a1 = 4.3x10^-7 and neglecting the second ionisation and ionisation of water. JEE Main level
• For H3PO4: pK_a1 = 2.15, pK_a2 = 7.21, pK_a3 = 12.35. Using the amphiprotic formula, the pH of a solution of disodium hydrogenphosphate, Na2HPO4, is approximate... JEE Main level
• Sodium sulfite is 0.15 M in water at 298 K. K_a2 of H2SO3 is 6.2x10^-8 (K_w = 1.0x10^-14). Considering only the first hydrolysis step of SO3^2- and using [OH-] ... JEE Main level
• A diprotic acid H2A has K_a1 = 5.0x10^-3 and a negligible K_a2. Calculate the pH of a 0.10 M solution of H2A by solving the quadratic for the first ionisation e... JEE Main level
• A phosphate buffer has pH 7.60. For the pair H2PO4-/HPO4^2-, pK_a2 = 7.20. Calculate the ratio [HPO4^2-]/[H2PO4-] to two decimal places. JEE Main level
• Which of the following species can behave both as a Bronsted acid and as a Bronsted base in water? JEE Main level
• 100 mL of 0.10 M H3PO4 is mixed with 180 mL of 0.10 M NaOH at 298 K. pK_a1 = 2.12, pK_a2 = 7.21, pK_a3 = 12.32; use log 2 = 0.301. The pH of the mixture is clos... JEE Advanced level
• A solution is 0.010 M in Zn^2+ and saturated with H2S ([H2S] = 0.10 M). Use K_a1K_a2 = 1.0x10^-21 for H2S and K_sp(ZnS) = 3.0x10^-23. The highest pH at which no... JEE Advanced level
• A 0.10 M solution of the sodium salt NaHA of a diprotic acid H2A (with pK_a1 = 1.90) has a measured pH of 4.00 at 298 K. Assuming the amphiprotic formula applie... JEE Advanced level
• A saturated solution of H2S ([H2S] = 0.10 M) is buffered at pH 3.00. With K_a1 = 9.1x10^-8 and K_a2 = 1.2x10^-13, find [S^2-] and report it in units of 10^-15 M... JEE Advanced level
• Treat H2SO4 as fully ionised in its first step and HSO4- as a weak acid with K_a2 = 1.2x10^-2. For a 0.10 M H2SO4 solution, solve the second equilibrium exactly... JEE Advanced level
• A 0.10 M solution of NaHA is prepared, where H2A has pK_a1 = 3.0 and pK_a2 = 7.0 (298 K). Use the standard amphiprotic approximation, [H+] = sqrtK_a1K_a2. Selec... JEE Advanced level
• A 0.10 M Na2CO3 solution at 298 K is analysed using K_a1 = 4.3x10^-7 and K_a2 = 4.7x10^-11 for H2CO3. Take [OH-] = sqrtK_h1c and neglect the second hydrolysis f... JEE Advanced level
• Sodium hydrogencarbonate is amphiprotic. For H2CO3, pK_a1 = 6.4 and pK_a2 = 10.2. Taking the pH of an amphiprotic salt solution as tfrac12(pK_a1+pK_a2), the pH ... NEET level
• Which one of the following species can act both as a Bronsted acid and as a Bronsted base in water? NEET level
• For H2S, K_a1 = 1.0x10^-7 and K_a2 = 1.0x10^-14. Neglecting the second ionisation, the pH of 0.1 M H2S is NEET level
• A 0.1 M solution of a weak diprotic acid H2A has K_a1 = 1.0x10^-5 and K_a2 = 1.0x10^-10. In this solution (no other acid or base added) the concentration of A^2... NEET level
• The diprotic acid H2A has K_a1 = 4.0x10^-3 and K_a2 = 1.0x10^-9. For a 0.100 M solution, neglect the second ionisation and solve the first-step quadratic exactl... JEE Main level
• A saturated solution of H2S ([H2S] = 0.10 M) is buffered at pH = 3.0. Given K_a1K_a2 = 1.0x10^-21, the concentration of S^2- is JEE Main level
• For H3PO4, pK_a2 = 7.21 and pK_a3 = 12.35. Treating HPO4^2- as an amphiprotic species with pH = tfrac12(pK_a2+pK_a3), find the pH of an aqueous Na2HPO4 solution... JEE Main level
• For H3PO4, pK_a1 = 2.15, pK_a2 = 7.21, pK_a3 = 12.35. Using pH = tfrac12(pK_before+pK_after) for amphiprotic ions, select the correct statement(s). JEE Main level
• A diprotic acid H2A has pK_a1 = 4.0 and pK_a2 = 8.0. The fraction of the total acid present as HA- at pH = 5.0 is closest to JEE Main level
• For H2CO3, K_a2 = 4.7x10^-11 and K_w = 1.0x10^-14. Neglecting the second hydrolysis step of CO3^2- and solving the first-step quadratic exactly, find the pH of ... JEE Main level
• Given K_w = 1.0x10^-14; for H2CO3: K_a1 = 4.3x10^-7, K_a2 = 4.7x10^-11; for H3PO4: K_a1 = 7.5x10^-3, K_a2 = 6.2x10^-8. Select the correct statement(s) about aqu... JEE Main level
• Sulfuric acid is taken as completely ionised in the first step, with K_a2 = 1.2x10^-2 for HSO4-. The pH of 0.10 M H2SO4 (second step solved exactly) is JEE Advanced level
• For H3PO4: K_a1 = 7.1x10^-3, K_a2 = 6.3x10^-8, K_a3 = 4.2x10^-13. In a 0.100 M solution of H3PO4 (no other species added), solve the first step as an exact quad... JEE Advanced level
• A diprotic acid H2A has pK_a1 = 3.0 and pK_a2 = 7.0. Select the correct statement(s). JEE Advanced level
• 100 mL of 0.10 M H2A (pK_a1 = 3.00, pK_a2 = 7.00) is titrated with 0.10 M NaOH. The volume of base needed to bring the pH to 7.00 is closest to JEE Advanced level
• 0.0100 mol of Na2CO3 is dissolved in water and 0.0120 mol of HCl is added; the final volume is 100 mL. Given pK_a1 = 6.35 and pK_a2 = 10.33 for H2CO3 and log 2 ... JEE Advanced level
• Hydrogen sulfide is bubbled into 0.20 M HCl until [H2S] = 0.10 M. Taking [H+] = 0.20 M and K_a1K_a2 = 1.0x10^-21, the concentration of S^2- is JEE Advanced level
• Take the first ionisation of H2SO4 as complete and K_a2 = 1.2x10^-2 for HSO4-. Select the correct statement(s). JEE Advanced level