Reactions of acids with metals, carbonates, oxides and hydroxides
Acids react with four kinds of substance to make salts. Each combination has its own general equation and signature observation. The salt formed depends on the acid (its anion) and the metal (its cation).
The general equations
- Acid + metal → salt + hydrogen (only metals above H in reactivity series)
- Acid + metal carbonate → salt + water + carbon dioxide
- Acid + metal oxide → salt + water
- Acid + metal hydroxide → salt + water
Naming salts
The acid sets the second part of the salt's name:
- Hydrochloric acid (HCl) → chloride salts.
- Sulfuric acid (H₂SO₄) → sulfate salts.
- Nitric acid (HNO₃) → nitrate salts.
So Mg + 2HCl → MgCl₂ (magnesium chloride) + H₂.
Reactions in detail
Acid + metal
Mg + 2HCl → MgCl₂ + H₂ Observations: bubbles of hydrogen, metal disappears, slight warming. Test for H₂: lit splint → squeaky pop.
Acid + metal carbonate
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ Observations: vigorous bubbles, fizzing. Test CO₂: bubble through limewater → turns cloudy.
Acid + metal oxide
CuO + H₂SO₄ → CuSO₄ + H₂O Observations: black CuO dissolves; solution turns blue. (Often warm the acid first.)
Acid + metal hydroxide (neutralisation)
NaOH + HCl → NaCl + H₂O Observations: temperature rises (exothermic). pH approaches 7.
✦Worked example— Worked example — predicting products
What forms when zinc carbonate is added to nitric acid?
- Zinc carbonate = ZnCO₃; nitric acid = HNO₃.
- Products: zinc nitrate (Zn(NO₃)₂) + water + carbon dioxide.
Balanced: ZnCO₃ + 2HNO₃ → Zn(NO₃)₂ + H₂O + CO₂.
Soluble vs insoluble
Most chlorides, nitrates and sulfates are soluble (a few exceptions: AgCl, PbCl₂, BaSO₄, PbSO₄). Most carbonates and hydroxides are insoluble (except group 1 and ammonium). This matters for choosing the right method to make a pure salt (C4.5–C4.6).
⚠Common mistakes
- Forgetting the brackets for ions like nitrate when the metal is 2+: write Mg(NO₃)₂, not MgNO₃₂.
- Using "salt + water" for metal carbonates (no — also CO₂).
- Saying the reaction with a metal makes water (no — it makes hydrogen gas).
- Mixing up salt names: HCl makes chloride, H₂SO₄ makes sulfate, HNO₃ makes nitrate.
Links
Sets up C4.5–C4.6 (preparing pure salt samples), C4.7 (pH and titrations), C8.3 (gas tests).
AI-generated · claude-opus-4-7 · v3-deep-chemistry