formed on ionization of salts either exist as hydrated ions in aqueous solutions or interact with water to reform corresponding acids/ bases depending upon the nature of salts. The later process of interaction between water and cations/anions or both of salts is called hydrolysis. The pH of the solution gets affected by this interaction.
-- NCERT Class 11 Chemistry, Ch. 6, p. 202Hydrolysis of Salts
8 MCQs9-step worked example
Source: NCERT EquilibriumPYQ coverage: NEET 2021Official key: NTA-verifiedLast updated: 7 Oct 2026
Try this first
Which of the following salts gives a neutral aqueous solution with pH 7, because neither of its ions hydrolyses?
- A.CH₃COONa
- B.KNO₃
- C.NH₄Cl
- D.CH₃COOK
Tap to see the answer
Answer: B. KNO₃ is a salt of a strong base (KOH) and a strong acid (HNO₃). Its ions K⁺ and NO₃⁻ only get hydrated, so the solution is neutral (NCERT Class 11 Chemistry, Chapter 6, page 202).
A is wrong: A is wrong because CH₃COONa is a salt of a weak acid and a strong base; the acetate ion hydrolyses and the pH is more than 7 (NCERT Class 11 Chemistry, Chapter 6, page 202).
C is wrong: C is wrong because NH₄Cl is a salt of a weak base and a strong acid; NH₄⁺ hydrolyses and the pH is less than 7 (NCERT Class 11 Chemistry, Chapter 6, page 202).
D is wrong: D is wrong because CH₃COOK, like CH₃COONa, has a weak-acid anion that hydrolyses and gives an alkaline solution (trap: judging the salt by its metal ion alone).
Hydrolysis of Salts, explained for NEET
The trap is guessing the pH of a salt from its name. A salt is not "neutral" just because it is a salt. The pH depends on which ions hydrolyse, and for a salt of a weak acid and a weak base it depends on a difference of two pK values.
Hydrolysis is the interaction of the cations, the anions, or both, of a salt with water; it changes the pH of the solution (NCERT Class 11 Chemistry, Chapter 6, page 202).
Strong acid with strong base: ions such as Na⁺, K⁺, Cl⁻ and NO₃⁻ only get hydrated and do not hydrolyse, so the solution is neutral, pH 7 (NCERT Class 11 Chemistry, Chapter 6, page 202).
Weak acid with strong base, for example CH₃COONa: the acetate ion reacts with water to give CH₃COOH and OH⁻. Acetic acid stays mostly unionised, OH⁻ builds up, and the pH is more than 7 (NCERT Class 11 Chemistry, Chapter 6, page 202).
Strong acid with weak base, for example NH₄Cl: NH₄⁺ reacts with water to give NH₄OH and H⁺. The weak base stays mostly unionised, H⁺ builds up, and the pH is less than 7 (NCERT Class 11 Chemistry, Chapter 6, page 202).
Weak acid with weak base, for example CH₃COONH₄: both ions hydrolyse. NCERT states that the degree of hydrolysis is independent of the concentration of the solution, and the pH is set by the pK values: pH = 7 + ½(pKa − pKb). It is greater than 7 if the difference is positive and less than 7 if negative (NCERT Class 11 Chemistry, Chapter 6, page 202). For pKa = 4.76 and pKb = 4.75, NCERT gets 7.005.
Watch out: pKa comes first in the bracket. Reversing the order flips the sign of the correction, and dropping the ½ doubles it.
How do you solve a Hydrolysis of Salts question? A worked example
- 1
Given
The pKb of dimethylamine is 3.27 and the pKa of acetic acid is 4.77 at the same temperature. The salt dimethylammonium acetate is dissolved in water. (This is the pattern of a NEET 2021 question.)
- 2
Required
The pH of the dimethylammonium acetate solution.
- 3
Concept
The salt comes from a weak acid and a weak base, so both ions hydrolyse and the pH is set by the two pK values (NCERT Class 11 Chemistry, Chapter 6, page 202).
- 4
Formula
pH = 7 + ½(pKa − pKb)
- 5
Substitution
pH = 7 + ½(4.77 − 3.27)
- 6
Calculation
4.77 − 3.27 = 1.50, and ½ × 1.50 = 0.75, so pH = 7 + 0.75 = 7.75. The ½ and the 7 are exact and do not limit the significant figures.
- 7
Final answer
pH = 7.75. It is more than 7 because pKa is larger than pKb, so the acid is the weaker of the two.
- 8
Common trap
Reversing the bracket gives 7 − 0.75 = 6.25, and dropping the ½ gives 7 + 1.50 = 8.50. Both are wrong options a hurried student can land on.
- 9
Similar NEET-style question
Ammonium formate is a salt of formic acid (pKa = 3.75) and ammonia (pKb = 4.75). Is its solution acidic or alkaline, and what is the pH? (Answer: pH = 7 + ½(3.75 − 4.75) = 7 + ½(−1.00) = 7 − 0.50 = 6.50, so the solution is acidic because the acid is stronger than the base.)
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Can you answer these Hydrolysis of Salts MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
Which of the following salts gives a neutral aqueous solution with pH 7, because neither of its ions hydrolyses?
Show answer and why every option is right or wrong
Answer: B. KNO₃ is a salt of a strong base (KOH) and a strong acid (HNO₃). Its ions K⁺ and NO₃⁻ only get hydrated, so the solution is neutral (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why A is wrong: A is wrong because CH₃COONa is a salt of a weak acid and a strong base; the acetate ion hydrolyses and the pH is more than 7 (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why C is wrong: C is wrong because NH₄Cl is a salt of a weak base and a strong acid; NH₄⁺ hydrolyses and the pH is less than 7 (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why D is wrong: D is wrong because CH₃COOK, like CH₃COONa, has a weak-acid anion that hydrolyses and gives an alkaline solution (trap: judging the salt by its metal ion alone).
MCQ 2Easy RecallPractice
In the context of salts, what does hydrolysis mean?
Show answer and why every option is right or wrong
Answer: D. NCERT defines hydrolysis as the interaction between water and the cations, anions or both of a salt, which affects the pH of the solution (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why A is wrong: A is wrong because ions that merely get hydrated, such as those of a strong acid and strong base salt, do not hydrolyse (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why B is wrong: B is wrong because that describes neutralisation, which forms the salt; hydrolysis acts on the salt after it forms (trap: confusing the formation of a salt with its hydrolysis).
Why C is wrong: C is wrong because losing water of crystallisation is a heating effect and has nothing to do with hydrolysis.
MCQ 3Easy RecallPractice
An aqueous solution of CH₃COONa is alkaline because
Show answer and why every option is right or wrong
Answer: A. The acetate ion hydrolyses: CH₃COO⁻ + H₂O ⇌ CH₃COOH + OH⁻. Acetic acid is weak and stays mostly unionised, so OH⁻ increases and the pH is more than 7 (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why B is wrong: B is wrong because Na⁺ is the cation of a strong base and does not hydrolyse (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why C is wrong: C is wrong because CH₃COONa is completely ionised in aqueous solution; the alkalinity comes from the hydrolysis of the acetate ion (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why D is wrong: D is wrong because only the anion hydrolyses here; the sodium ion is from a strong base and stays hydrated (trap: treating a weak-acid and strong-base salt like a weak-acid and weak-base salt).
MCQ 4Direct ApplicationPractice
Equal-concentration aqueous solutions of KCl, NH₄Cl and CH₃COONa are compared. Which order of pH is correct?
Show answer and why every option is right or wrong
Answer: C. CH₃COONa is alkaline (pH more than 7), KCl is neutral (pH 7) and NH₄Cl is acidic (pH less than 7), so CH₃COONa > KCl > NH₄Cl (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why A is wrong: A is wrong because it reverses the acidic and alkaline cases: NH₄Cl is acidic and CH₃COONa is alkaline (trap: swapping which ion raises H⁺ and which raises OH⁻).
Why B is wrong: B is wrong because it places the acidic NH₄Cl above the alkaline CH₃COONa; NH₄Cl has pH less than 7 (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why D is wrong: D is wrong because NH₄Cl is acidic and must lie below the neutral KCl, not above it (NCERT Class 11 Chemistry, Chapter 6, page 202).
MCQ 5Direct ApplicationPractice
A salt is formed from a weak acid with pKa = 5.0 and a weak base with pKb = 6.0. What is the pH of its aqueous solution?
Show answer and why every option is right or wrong
Answer: C. pH = 7 + ½(pKa − pKb) = 7 + ½(5.0 − 6.0) = 7 − 0.50 = 6.5 (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why A is wrong: A is wrong because 8.0 comes from 7 + (6.0 − 5.0), which reverses the bracket and drops the ½ (trap: reversing pKa and pKb and dropping ½).
Why B is wrong: B is wrong because 7.5 reverses the bracket to pKb − pKa and keeps the ½ (trap: reversing pKa and pKb).
Why D is wrong: D is wrong because 6.0 drops the ½: 7 + (5.0 − 6.0) = 6.0 (trap: dropping the factor ½).
MCQ 6Direct ApplicationPractice
An aqueous solution of ammonium acetate, a salt of a weak acid and a weak base, is diluted ten times with water. What happens to its pH?
Show answer and why every option is right or wrong
Answer: A. For a weak acid and weak base salt the degree of hydrolysis is independent of concentration, and the pH is fixed by pKa and pKb, so dilution does not move it appreciably (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why B is wrong: B is wrong because a one-unit rise would follow if the pH depended on concentration as it does for a strong base; here only pKa and pKb appear in the formula (trap: assuming dilution always moves pH).
Why C is wrong: C is wrong because a one-unit fall assumes pH tracks concentration like a strong acid; the formula contains no concentration term (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why D is wrong: D is wrong because the formula 7 + ½(pKa − pKb) contains no concentration, so there is no half-unit shift on dilution (trap: confusing the factor ½ in the formula with a dilution effect).
MCQ 7CalculationPractice
A weak acid has pKa = 6.8 and a weak base has pKb = 4.2. What is the pH of the solution of the salt they form?
Show answer and why every option is right or wrong
Answer: D. The difference is pKa − pKb = 6.8 − 4.2 = 2.6. Then pH = 7 + ½(2.6) = 7 + 1.3 = 8.3, which is more than 7 because the difference is positive (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why A is wrong: A is wrong because 7 − ½(2.6) = 5.7 uses the opposite sign; a positive pKa − pKb gives pH more than 7 (trap: reversing pKa and pKb).
Why B is wrong: B is wrong because 7 + 2.6 = 9.6 drops the ½ (trap: dropping the factor ½).
Why C is wrong: C is wrong because 7 − 2.6 = 4.4 both reverses the sign and drops the ½ (trap: reversing pKa and pKb and dropping ½).
MCQ 8CalculationPractice
A weak acid has Ka = 1.0 × 10⁻⁴ and a weak base has Kb = 1.0 × 10⁻⁸. What is the pH of the solution of their salt?
Show answer and why every option is right or wrong
Answer: B. pKa = −log(1.0 × 10⁻⁴) = 4.0 and pKb = −log(1.0 × 10⁻⁸) = 8.0. Then pH = 7 + ½(4.0 − 8.0) = 7 − 2.0 = 5.0, which is less than 7 because the acid is the stronger of the two (NCERT Class 11 Chemistry, Chapter 6, page 202).
Why A is wrong: A is wrong because 7 + ½(8.0 − 4.0) = 9.0 reverses the bracket (trap: reversing pKa and pKb).
Why C is wrong: C is wrong because 7 + (4.0 − 8.0) = 3.0 drops the ½ (trap: dropping the factor ½).
Why D is wrong: D is wrong because 7 + (8.0 − 4.0) = 11.0 both reverses the bracket and drops the ½ (trap: reversing pKa and pKb and dropping ½).
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What to remember before solving Hydrolysis of Salts questions
5 NCERT lines
The cations (e.g., Na+, K+, Ca2+, Ba2+, etc.) of strong bases and anions (e.g., Cl–, Br–, NO3 –, ClO4 – etc.) of strong acids simply get hydrated but do not hydrolyse, and therefore the solutions of salts formed from strong acids and bases are neutral i.e., their pH is 7.
-- NCERT Class 11 Chemistry, Ch. 6, p. 202Key Fact
Salt of weak acid and strong base (CH3COONa): acetate hydrolyses, solution alkaline, pH more than 7
In the first case, CH3COONa being a salt of weak acid, CH3COOH and strong base, NaOH gets completely ionised in aqueous solution. CH3COONa(aq) → CH3COO– (aq)+ Na+(aq) Acetate ion thus formed undergoes hydrolysis in water to give acetic acid and OH– ions CH3COO–(aq)+H2O(l) CH3COOH(aq)+OH–(aq) Acetic acid being a weak acid (Ka = 1.8 × 10–5) remains mainly unionised in solution. This results in increase of OH– ion concentration in solution making it alkaline. The pH of such a solution is more than 7.
-- NCERT Class 11 Chemistry, Ch. 6, p. 202Key Fact
Salt of strong acid and weak base (NH4Cl): ammonium hydrolyses, solution acidic, pH less than 7
Similarly, NH4Cl formed from weak base, NH4OH and strong acid, HCl, in water dissociates completely. NH4Cl(aq) → NH + 4(aq) +Cl– (aq) Ammonium ions undergo hydrolysis with water to form NH4OH and H+ ions NH + 4 (aq) + H2O (1) NH4OH(aq) + H+(aq) Ammonium hydroxide is a weak base (Kb = 1.77 × 10–5) and therefore remains almost unionised in solution. This results in increased of H+ ion concentration in solution making the solution acidic. Thus, the pH of NH4Cl solution in water is less than 7.
-- NCERT Class 11 Chemistry, Ch. 6, p. 202For a salt of a weak acid and a weak base (e.g. CH3COONH4), the degree of hydrolysis is independent of concentration and the pH is determined by pKa and pKb: pH = 7 + ½(pKa - pKb). The pH is greater than 7 if the difference is positive, and less than 7 if it is negative.
-- NCERT Class 11 Chemistry, Ch. 6, p. 202Hydrolysis of Salts: NEET previous year questions (PYQs) with answers
1 question from NEET 2021, answers verified against NTA official keys
NEET 2021
16.25
28.50
35.50
47.75
NTA Answer: Option 4(final)
Why the other options are wrong
- Option 1: 6.25 reverses the sign. For a salt of weak acid and weak base pH = 7 + ½ (pKa – pKb) = 7 + ½(4.77 – 3.27) = 7.75.
- Option 2: 8.50 drops the ½: 7 + (4.77 – 3.27) = 8.5. The formula is pH = 7 + ½ (pKa – pKb), which gives 7.75.
- Option 3: 5.50 subtracts the full difference. The difference 4.77 – 3.27 is positive, and the pH of solution can be greater than 7, if the difference is positive: 7 + 0.75 = 7.75.
More in Equilibrium: 8 exam traps and mistakes · 5 formulas · 4 question patterns from its other lessons.
Sources
NCERT refs: Class 11 Chemistry Chapter 6, p.202
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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