A7LAM CSCA ACADEMYCSCA Academy / Chemistry / Substances and their reactions
CSCA Chemistry · Lesson 7 of 21Non-metals and their compounds
Les non-métaux et leurs composés · اللافلزات ومركباتها
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Chlorine, sulfur, nitrogen and silicon form many everyday compounds. Learn their key reactions and how to recognise them.
Key ideas
- Chlorine: yellow-green, toxic; Cl₂ + H₂O ⇌ HCl + HClO (HClO bleaches).
- Sulfur: SO₂ bleaches magenta dye and causes acid rain; concentrated H₂SO₄ dehydrates and oxidises.
- Nitrogen: NH₃ is basic (turns damp red litmus blue); HNO₃ is a strong oxidising acid.
- Silicon: SiO₂ is in sand and glass; Si is a semiconductor.
Formulas to know
- MnO₂ + 4HCl(conc) → MnCl₂ + Cl₂↑ + 2H₂O (heat)
- Cu + 2H₂SO₄(conc) → CuSO₄ + SO₂↑ + 2H₂O (heat)
- 3Cu + 8HNO₃(dilute) → 3Cu(NO₃)₂ + 2NO↑ + 4H₂O
Worked example
How can you tell SO₂ from CO₂?
- Both: both gases turn limewater milky
- Difference: SO₂ bleaches magenta (fuchsine) solution; CO₂ does not
- Test: bubble each gas through magenta solution
Answer: SO₂ decolourises magenta solution
Practice questions
1. Which gas turns damp red litmus paper blue?
HCl · NH₃ ✓ · SO₂ · Cl₂
NH₃ is the common basic gas.
2. Concentrated H₂SO₄ turns sugar black. This shows it is:
a dehydrating agent ✓ · a base · a reducing agent · volatile
It removes H and O as water.
3. The main compound in sand is:
Si · SiO₂ ✓ · CaCO₃ · Na₂CO₃
Silicon dioxide.