Inorganic substances and their transformations
Domain 4 - anorgaanilised ained ja nende muundumised - covers oxides, acids, bases, salts and metals, and the reaction patterns that connect them. Exam tasks ask you to name a compound, predict whether a reaction happens, or write the products.
Classes and naming
- Oxides: basic (metal + oxygen, e.g. Na₂O, CaO, CuO) react with acids; acidic (non-metal, e.g. CO₂, SO₂, SO₃) react with bases and water; amphoteric (Al₂O₃, ZnO) react with both.
- Bases/hydroxides contain OH⁻: NaOH, KOH, Ca(OH)₂. Soluble bases are alkalis (leelised).
- Acids contain H: HCl (vesinikkloriidhape), H₂SO₄, HNO₃, H₂CO₃, H₃PO₄.
- Salts: metal (or NH₄⁺) + acid residue - NaCl, CaSO₄, FeCl₃ (iron(III) chloride).
Reaction patterns
- Basic oxide + acid → salt + water: CuO + H₂SO₄ → CuSO₄ + H₂O.
- Acidic oxide + base → salt + water: CO₂ + 2NaOH → Na₂CO₃ + H₂O.
- Acid + base → salt + water (neutralisation).
- Metal + acid → salt + H₂, only if the metal is above hydrogen in the activity series (K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb, H, Cu, Ag, Au).
- Salt + salt → two new salts when one is insoluble: AgNO₃ + KCl → AgCl↓ + KNO₃.
- Metal + oxygen → oxide; metal + water → hydroxide + H₂ for the most active metals (Na, K, Ca).
Worked example
Will copper react with dilute hydrochloric acid? Give the equation if it will. The activity series puts Cu below H, so copper cannot displace hydrogen from an acid: no reaction. Zinc, above hydrogen, does react: Zn + 2HCl → ZnCl₂ + H₂, showing bubbles of hydrogen and the zinc dissolving. In ionic form: Zn + 2H⁺ → Zn²⁺ + H₂.
Traps that cost marks
- Writing 'metal + acid → salt + H₂O' - the gas is hydrogen.
- Ignoring the activity series and reacting gold with acid.
- Forgetting that aluminium oxide is amphoteric.
- Naming FeCl₂ as iron chloride - it is iron(II) chloride.
- Treating concentrated H₂SO₄ as if it behaved like the dilute acid: hot concentrated acid oxidises copper and gives SO₂ instead of H₂.