Topic 6 of 8 · Form 3
Acids, bases and salts
Acids are proton (H⁺) donors; bases are proton acceptors. Alkalis release OH⁻ in solution. pH scale, universal indicator; strong and weak acids (degree of ionisation).
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Acids and bases
Acids are proton (H⁺) donors; bases are proton acceptors. Alkalis release OH⁻ in solution. pH scale, universal indicator; strong and weak acids (degree of ionisation).
Reactions
Acids with metals (salt + hydrogen), bases (salt + water), carbonates (salt + water + CO₂). Neutralisation: H⁺ + OH⁻ → H₂O.
Oxides
Basic (metal oxides), acidic (non-metal oxides), amphoteric (Al₂O₃, ZnO) and neutral (CO, N₂O).
Preparing salts
- Soluble salts: excess insoluble base/metal/carbonate + acid, filter, crystallise; or titration for Group I salts.
- Insoluble salts: precipitation.
Solubility rules
All sodium, potassium and ammonium salts and all nitrates are soluble; most chlorides except silver and lead; most sulfates except barium, calcium and lead; most carbonates insoluble except Group I and ammonium.
Qualitative analysis
Tests for cations (NaOH and NH₃ precipitates: Cu²⁺ blue, Fe²⁺ green, Fe³⁺ red-brown, Zn²⁺/Al³⁺ white – Zn²⁺ soluble in excess ammonia), anions (carbonate, chloride, bromide, iodide, sulfate, nitrate) and gases.
Check yourself
- Name the precipitate colour when NaOH is added to Fe³⁺ ions.
- Which method makes barium sulfate?
- Is zinc oxide acidic, basic or amphoteric?
Show answers
- Red-brown.
- Precipitation.
- Amphoteric.
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