⚖️ Reactions of Metals
Metals react with other substances to form compounds.
The reactivity of a metal depends on how easily it loses electrons to form positive ions.
Reactivity series (most to least reactive):
Potassium
Sodium
Calcium
Magnesium
Aluminium
(Carbon)
Zinc
Iron
Tin
Lead
(Hydrogen)
Copper
Silver
Gold
Platinum
Rules to remember:
- Metals above hydrogen in the series react with acids to form hydrogen gas.
- Metals above carbon can only be extracted using electrolysis.
Example reaction with acid:
magnesium + hydrochloric acid → magnesium chloride + hydrogen
Mg + 2HCl → MgCl₂ + H₂
🔋 Redox Reactions
A redox reaction involves reduction and oxidation happening at the same time.
- Oxidation: gain of oxygen or loss of electrons.
- Reduction: loss of oxygen or gain of electrons.
OILRIG:
Oxidation Is Loss (of electrons)
Reduction Is Gain (of electrons)
Example:
Mg → Mg²⁺ + 2e⁻ (oxidation)
2H⁺ + 2e⁻ → H₂ (reduction)
⚔️ Metal Displacement Reactions
A more reactive metal displaces a less reactive one from its compound.
Example:
magnesium + copper sulfate → magnesium sulfate + copper
Mg + CuSO₄ → MgSO₄ + Cu
This shows magnesium is more reactive than copper.
🧱 Metals and Acids
When metals react with acids, they form a salt and hydrogen gas.
General formula:
metal + acid → salt + hydrogen
Examples:
- magnesium + hydrochloric acid → magnesium chloride + hydrogen
- zinc + sulfuric acid → zinc sulfate + hydrogen
Test for hydrogen: a lit splint makes a “squeaky pop” sound.
🔥 Reactions of Acids with Bases and Carbonates
Acids react with:
- Bases (metal oxides/hydroxides) → salt + water
- Carbonates → salt + water + carbon dioxide
Examples:
- hydrochloric acid + sodium hydroxide → sodium chloride + water
HCl + NaOH → NaCl + H₂O - sulfuric acid + copper carbonate → copper sulfate + water + carbon dioxide
H₂SO₄ + CuCO₃ → CuSO₄ + H₂O + CO₂
🧪 Making Salts (Required Practical)
Aim: Prepare a pure, dry sample of a soluble salt (e.g. copper sulfate).
Method:
- Add excess insoluble base (copper oxide) to acid (sulfuric acid).
- Stir and gently heat.
- Filter to remove excess solid.
- Evaporate the filtrate until crystals form.
- Leave to crystallise.
Equation:
H₂SO₄ + CuO → CuSO₄ + H₂O
⚡ The Reactivity Series and Extraction
- Metals above carbon (like aluminium) must be extracted using electrolysis.
- Metals below carbon (like iron) can be extracted using reduction with carbon.
Example:
iron oxide + carbon → iron + carbon dioxide
Fe₂O₃ + 3C → 2Fe + 3CO₂
⚡ Electrolysis
Electrolysis uses electricity to split compounds into elements.
It happens in an electrolyte – an ionic compound in molten or dissolved form.
- Anode (+): negative ions (anions) lose electrons (oxidation).
- Cathode (–): positive ions (cations) gain electrons (reduction).
Example:
electrolysis of molten lead bromide (PbBr₂):
At cathode: Pb²⁺ + 2e⁻ → Pb
At anode: 2Br⁻ → Br₂ + 2e⁻
💧 Electrolysis of Aqueous Solutions
In aqueous (water-based) electrolysis, water ions also take part.
At the cathode (–):
- Hydrogen forms if the metal is more reactive than hydrogen.
At the anode (+):
- Oxygen forms unless halide ions (Cl⁻, Br⁻, I⁻) are present.
Example: electrolysis of sodium chloride solution (brine):
- Cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻
- Anode: 2Cl⁻ → Cl₂ + 2e⁻
⚙️ Electrolysis of Aluminium Oxide
Used to extract aluminium from bauxite ore.
- Aluminium oxide is mixed with cryolite to lower its melting point.
- Aluminium forms at the cathode.
- Oxygen forms at the anode and reacts with the carbon electrodes, forming CO₂.
Equations:
Cathode: Al³⁺ + 3e⁻ → Al
Anode: 2O²⁻ → O₂ + 4e⁻
⚡ Required Practical – Electrolysis
Aim: Investigate electrolysis of copper sulfate solution.
Method:
- Use inert electrodes (carbon or platinum).
- Connect to power supply.
- Observe copper forming on the cathode.
- Oxygen (or chlorine) gas forms at the anode depending on solution.
Half-equations:
Cathode: Cu²⁺ + 2e⁻ → Cu
Anode: 4OH⁻ → O₂ + 2H₂O + 4e⁻
