CBSE Class 10 Science: Acids, Bases and Salts (CBSE) — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: How do acids and bases react with metals? Give equations.
  Ans: Acid + Metal → Salt + Hydrogen gas. Example: 2HCl + Zn → ZnCl₂ + H₂↑. Active metals like Zn, Mg, Fe react; noble metals like Au, Pt don't. Base + Metal → Salt + Hydrogen (only certain metals like Zn, Al react with bases). Example: 2NaOH + Zn → Na₂ZnO₂ + H₂↑. Note: HNO₃ reacts differently with metals — does not produce H₂.
• Q: What happens when metal carbonates and bicarbonates react with acids?
  Ans: Metal carbonate + Acid → Salt + Water + CO₂↑. Example: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑. Metal bicarbonate + Acid → Salt + Water + CO₂↑. Example: NaHCO₃ + HCl → NaCl + H₂O + CO₂↑. Test: CO₂ turns lime water milky — Ca(OH)₂ + CO₂ → CaCO₃↓ (white) + H₂O.
• Q: Explain the pH scale. What is the pH of (i) pure water, (ii) gastric juice, (iii) blood?
  Ans: pH scale measures hydrogen ion concentration, ranging from 0-14. pH = -log[H⁺]. pH < 7: Acidic (more H⁺ ions). pH = 7: Neutral. pH > 7: Basic (more OH⁻ ions). Values: (i) Pure water: pH 7 (neutral). (ii) Gastric juice: pH ~1.2 (strongly acidic — HCl). (iii) Blood: pH 7.4 (slightly basic). Tooth decay starts below pH 5.5 when enamel (calcium phosphate) dissolves.

Long Answer / Application Questions (4-6 Marks)

• Q: How is Plaster of Paris prepared? Give its chemical formula and one use.
  Ans: Plaster of Paris (POP) is prepared by heating gypsum (CaSO₄.2H₂O) at 373 K. CaSO₄.2H₂O → (373K) → CaSO₄.½H₂O + 1½H₂O. Chemical name: Calcium sulphate hemihydrate. Formula: CaSO₄.½H₂O. When mixed with water, it sets into a hard mass (gypsum again). Uses: Making casts for broken bones, toys, decorative items, making moulds.

Exam Tips for This Chapter

• Revise all definitions and laws from Acids, Bases and Salts (CBSE) — they are commonly asked as 1-2 mark questions
• Practice diagrams related to Acids, Bases and Salts (CBSE) — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Acids, Bases and Salts (CBSE) carries 8-12 marks in the board exam