ICSE Class 10 Chemistry: Study of Compounds — HCl & HNO₃ Notes

Hydrochloric Acid (HCl)

• Preparation: NaCl + H₂SO₄ (conc) → NaHSO₄ + HCl↑ (at room temperature or gentle heat)
• Physical properties: colourless, pungent gas; fumes in moist air; very soluble in water
• Chemical properties: turns blue litmus red; reacts with metals (above H in activity series) to give H₂; neutralises alkalis

HCl Reactions with Metals and Bases

• Fe + 2HCl → FeCl₂ + H₂ (dilute HCl); Zn + 2HCl → ZnCl₂ + H₂
• NaOH + HCl → NaCl + H₂O (neutralisation); CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
• Test for HCl/chloride: HCl + AgNO₃ → AgCl (white precipitate, insoluble in dilute HNO₃)

Nitric Acid (HNO₃)

• Preparation: NaNO₃ + H₂SO₄ (conc) → NaHSO₄ + HNO₃ (heat gently)
• Physical properties: colourless liquid; fuming in air; turns yellow on standing (partial decomposition to NO₂)
• Concentrated HNO₃: strong oxidising agent; passivates Fe and Al (forms protective oxide layer)

HNO₃ Reactions

• Copper + dilute HNO₃: 3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO↑ + 4H₂O (colourless NO gas)
• Copper + conc HNO₃: Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂↑ + 2H₂O (brown fumes)
• Aqua regia: 3 parts conc HCl + 1 part conc HNO₃; dissolves noble metals (gold, platinum); oxidising ability of HNO₃ + complexing ability of HCl

Sulphuric Acid (H₂SO₄)

• Dilute H₂SO₄: acid properties; reacts with metals, bases, carbonates; cannot be made directly from SO₃ + H₂O directly (too vigorous)
• Concentrated H₂SO₄: dehydrating agent (removes water from compounds); oxidising agent (hot conc); drying agent
• Contact process: SO₂ + ½O₂ → SO₃ (V₂O₅ catalyst, 450°C); SO₃ + H₂SO₄ → H₂S₂O₇; + H₂O → 2H₂SO₄

Acid Rain

• SO₂ and NOₓ from power plants and vehicles dissolve in rainwater → sulphurous/sulphuric acid, nitric acid
• pH < 5.6: acid rain corrodes buildings (Taj Mahal threat), acidifies lakes and soils, damages crops
• Control: desulphurisation at power plants; catalytic converters in cars; switching to clean energy

ICSE Exam Focus

• Most commonly tested: HCl preparation equation, reactions with metals, HNO₃ with copper (dilute vs conc)
• Compare dilute vs concentrated H₂SO₄ and HNO₃: properties and reactions differ significantly
• Always write state symbols and balance equations; ICSE gives marks for correct equation