Chapter 2 · Question 10
What is meant by the 'family of salts'? How does the pH of a salt depend on the strengths of the acid and base from which it is formed? Give an example of each — an acidic salt, a basic salt, and a neutral salt.
Q10
What is meant by the 'family of salts'? How does the pH of a salt depend on the strengths of the acid and base from which it is formed? Give an example of each — an acidic salt, a basic salt, and a neutral salt.
Answer Revealed
Direct Answer:
Salts that share the same positive radical (cation, from the base) or the same negative radical (anion, from the acid) belong to the same family. For example, NaCl and belong to the sodium salts family (same cation), while NaCl and KCl belong to the chloride salts family (same anion). The pH of a salt depends on the relative strengths of its parent acid and base: a salt from a strong acid and strong base has pH = 7 (neutral, e.g., NaCl); from a strong acid and weak base has pH < 7 (acidic, e.g., ); from a weak acid and strong base has pH > 7 (basic, e.g., or ).
Simple Explanation
Think of salt families like surnames. Sodium chloride and sodium sulphate are both 'sodium' salts — they share the sodium () part coming from the base. Similarly, the pH of a salt tells you which parent was stronger. If both parents (acid and base) are strong, the child (salt) is neutral — like NaCl from HCl and NaOH. If the acid is strong but the base is weak, the salt turns out acidic. If the base is strong but the acid is weak, the salt is basic — like baking soda (), which has a basic pH.
Exam-Ready Structure
The classification of salts into families and the prediction of their pH from parent reactants are important analytical concepts in NCERT Class 10 Chapter 2. 1. Family of salts (Activity 2.13): (a) Salts that share the same cation (positive radical, derived from the base) or the same anion (negative radical, derived from the acid) are said to belong to the same family. (b) Example — sodium salts family: NaCl, , , — all contain the cation. (c) Example — chloride salts family: NaCl, KCl, , — all contain the anion. (d) Similarly, sulphate salts (, , , , ) share the anion and form the sulphate family. 2. pH of salts (Activity 2.14): The nature of a salt solution — whether it is acidic, basic, or neutral — is determined by the relative strengths of the acid and base from which the salt is derived. The rule is: (a) Salt of strong acid + strong base → neutral salt (pH = 7). Example: NaCl (from HCl + NaOH). (b) Salt of strong acid + weak base → acidic salt (pH < 7). Example: (from HCl + ), , , . (c) Salt of weak acid + strong base → basic salt (pH > 7). Example: (sodium acetate), (sodium carbonate), (sodium hydrogencarbonate). 3. Testing: Activity 2.14 instructs students to test the pH of various salts using litmus paper and pH paper, and to identify the parent acid and base for each salt. This builds the ability to reason backward from a salt to its parent reactants and predict its solution behaviour.
Key Points
- Family of salts: salts sharing same cation (e.g., Na⁺ in NaCl, Na₂SO₄) or same anion (e.g., Cl⁻ in NaCl, KCl)
- pH of salt depends on relative strengths of parent acid and base
- Strong acid + strong base neutral salt (pH = 7), e.g., NaCl
- Strong acid + weak base acidic salt (pH < 7), e.g., NH₄Cl, CuSO₄
- Weak acid + strong base basic salt (pH > 7), e.g., , Na₂CO₃
Common Mistakes
- Assuming all salts are neutral — the pH of a salt depends on the parent acid and base strengths
- Confusing the family classification — it is based on sharing a common radical (cation or anion), not on the colour or state of the salt
Related Questions
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What is a neutralisation reaction? Explain with the help of a simple activity involving sodium hydroxide and hydrochloric acid. Give the balanced chemical equation.
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