PYQs
Practise questions grouped by chapter and source year.
Practice questions are organised using the years and labels in our source collection. Work through the solutions with your teacher; these are not a complete official examination paper.
Practice question 1
Source year: 20251 marksHow is the concentration of hydroxide ions affected when excess base is dissolved in a solution of sodium hydroxide? [CBSE 2025]
Practice question 2
Source year: 20245 marksWhat is the chemical formula of (a) Plaster of Paris (b) Washing soda (c) Baking soda? Write one use of each. [CBSE 2024]
Practice question 3
Source year: 20233 marksWhat happens when a solution of acid is mixed with a solution of base in a test tube? Write the reaction involved. [CBSE 2023]
Practice question 4
Source year: 20223 marksWhy does tooth decay start when the pH of mouth is lower than 5.5? How can tooth decay be prevented? [CBSE 2022]
Practice question 5
Source year: 20212 marksWhat is meant by water of crystallization? Give two examples with their formulae. [CBSE 2021]
Formulae
Revisit important relationships and quick revision formulae.
pH Scale
pH = -log[H⁺] pH < 7: Acidic pH = 7: Neutral pH > 7: Basic Range: 0 to 14
Common Acids
HCl - Hydrochloric acid H₂SO₄ - Sulphuric acid HNO₃ - Nitric acid CH₃COOH - Acetic acid
Common Bases
NaOH - Sodium hydroxide KOH - Potassium hydroxide Ca(OH)₂ - Calcium hydroxide NH₄OH - Ammonium hydroxide
Important Salts
NaCl - Common salt Na₂CO₃.10H₂O - Washing soda NaHCO₃ - Baking soda CaSO₄.½H₂O - Plaster of Paris CaSO₄.2H₂O - Gypsum
Neutralization
Acid + Base → Salt + Water HCl + NaOH → NaCl + H₂O This is an exothermic reaction
Derivations
Work through the reasoning behind key concepts.
pH and its Importance
pH measures hydrogen ion concentration Lower pH = More acidic (more H⁺ ions) Higher pH = More basic (fewer H⁺ ions)
Importance:
- Human blood: pH 7.35-7.45
- Tooth enamel damaged below pH 5.5
- Soil pH affects plant growth
- pH of rain water (acid rain)
Preparation of Washing Soda
From baking soda: 2NaHCO₃ --heat--> Na₂CO₃ + H₂O + CO₂ Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O
Uses: Washing, glass making, removing hardness
Preparation of Plaster of Paris
From Gypsum (heating at 373K): CaSO₄.2H₂O --heat--> CaSO₄.½H₂O + 1½H₂O (Gypsum) (Plaster of Paris)
Uses: Casts, moulds, false ceiling
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