AQA Chemistry 5.4.1.1, 5.4.1.3 (+ 5.4.1.4 Higher) · Combined and Triple
Oxidation and reduction
Oxidation is gaining oxygen; reduction is losing it, and one never happens without the other. On Higher, the same two words describe electrons changing hands.
Triple Science · Higher tier
Start here
A rusty gate.
An iron gate left out in the weather goes rusty and flaky.
If you had to guess, has the iron gained something from the air, or lost something to it?
In terms of oxygen
Who gained it, who lost it.
Oxidation is the gain of oxygen; reduction is the loss of oxygen. A reaction in which both happen is called a redox reaction. Watch the oxygen move from copper oxide to hydrogen.
For each reactant, oxidised or reduced? The equations are balanced; check them as you go.
2Mg + O2 → 2MgO
Magnesium
Gained or lost oxygen?
CuO + H2 → Cu + H2O
Copper oxide
Gained or lost oxygen?
CuO + H2 → Cu + H2O
Hydrogen
Gained or lost oxygen?
2CuO + C → 2Cu + CO2
Copper oxide
Gained or lost oxygen?
2CuO + C → 2Cu + CO2
Carbon
Gained or lost oxygen?
Metals less reactive than carbon can be extracted from their oxides by reduction with carbon: Extraction of metals.
Higher · in terms of electrons
OIL RIG.
Oxidation Is Loss of electrons; Reduction Is Gain of electrons. The same card, with electrons instead of oxygen: magnesium displaces copper from copper sulfate solution.
Mg Mg2+ + 2e− loses electrons: oxidised
Cu2+ + 2e− Cu gains electrons: reduced
Mg + Cu2+ Mg2+ + Cu ionic equation; sulfate ions left out
Metals reacting with acids are redox too: Mg + 2H+ Mg2+ + H2. Which species is reduced?
Pick one.
Think again · the extractor
“Carbon is reduced when it takes the oxygen off a metal oxide.”
Your call
Choose2CuO + C → 2Cu + CO2. What happens to the carbon?
Sort
Oxidised or reduced?
Use the oxygen definitions.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Identify
- Which substance is oxidised and which is reduced, from a given equation.
- Explain
- Why, in terms of oxygen (or electrons on Higher).
- Write
- (Higher) an ionic equation for a displacement reaction.
Key fact
Oxidation is the gain of oxygen; reduction is the loss of oxygen. They always happen together. Higher: oxidation is loss of electrons, reduction is gain of electrons (OIL RIG).
Key note · AQA 5.4.1.1, 5.4.1.3 (+ 5.4.1.4 HT) · Combined and Triple
Oxidation and reduction
- Oxidation is the gain of oxygen; reduction is the loss of oxygen. They occur together: in CuO + H2 → Cu + H2O, copper oxide is reduced and hydrogen is oxidised.
- Metals react with oxygen to form metal oxides; the metal is oxidised (2Mg + O2 → 2MgO). Carbon reduces the oxides of less reactive metals (2CuO + C → 2Cu + CO2): the oxide is reduced, the carbon oxidised.
- Equations must balance. Chlorine and oxygen are Cl2 and O2.
- Higher: oxidation is loss of electrons, reduction is gain of electrons (OIL RIG). Mg → Mg²⁺ + 2e⁻ (oxidised); Cu²⁺ + 2e⁻ → Cu (reduced); ionic equation Mg + Cu²⁺ → Mg²⁺ + Cu.
- Higher: metals reacting with acids are redox: Mg + 2H⁺ → Mg²⁺ + H2, magnesium oxidised, hydrogen ions reduced.
Photograph this card. Tomorrow, cover it and say each line first.
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Calling the carbon reduced?
Every equation on this page is balanced; check the atoms.