A7LAM CSCA ACADEMYCSCA Academy / Chemistry / Substances and their reactions
CSCA Chemistry · Lesson 6 of 21Metals and their compounds
Les métaux et leurs composés · الفلزات ومركباتها
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Sodium, aluminium and iron are the metals that come up most. Know how they react with water, acids and bases, and the colours of their compounds.
Key ideas
- Sodium reacts with water: 2Na + 2H₂O → 2NaOH + H₂↑; Na₂O₂ releases O₂ with water and CO₂.
- Aluminium and Al₂O₃ are amphoteric: they react with acids and with strong bases.
- Iron: Fe²⁺ (pale green) is oxidised to Fe³⁺ (yellow-brown); Fe³⁺ + SCN⁻ turns red.
- Reactivity: K > Ca > Na > Mg > Al > Zn > Fe > Sn > Pb > (H) > Cu > Ag > Au.
Formulas to know
- 2Na + 2H₂O → 2NaOH + H₂↑
- 2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂↑
- 2Fe³⁺ + Fe → 3Fe²⁺
Worked example
2.3 g of sodium (M = 23 g/mol) reacts with water. Mass of hydrogen produced?
- Moles: n(Na) = 2.3 / 23 = 0.1 mol
- Ratio: 2Na → 1H₂, so n(H₂) = 0.05 mol
- Mass: m = 0.05 × 2 = 0.1 g
Answer: 0.1 g of H₂
Practice questions
1. Which metal does NOT react with dilute HCl?
Zn · Fe · Mg · Cu ✓
Cu is below H in the reactivity series.
2. Which substance reacts with both HCl and NaOH?
Fe₂O₃ · Al(OH)₃ ✓ · NaCl · CuO
Al(OH)₃ is amphoteric.
3. A solution turns red with KSCN. It contains:
Fe²⁺ · Fe³⁺ ✓ · Cu²⁺ · Al³⁺
The classic Fe³⁺ test.