Metals and oxygen
- Metals react with oxygen to form metal oxides, for example 2Mg + O₂ → 2MgO.
- Oxidation is the gain of oxygen. Reduction is the loss of oxygen.
The reactivity series
- When metals react, their atoms form positive ions. The more easily a metal forms positive ions, the more reactive it is.
- Order, most reactive first: potassium, sodium, lithium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen), copper, silver, gold.
- Potassium, sodium and lithium react with cold water; calcium reacts steadily; magnesium reacts very slowly with cold water.
- Metals above hydrogen react with dilute acids to make a salt and hydrogen; copper, silver and gold do not.
Displacement reactions
- A more reactive metal displaces a less reactive metal from a compound.
- Example: magnesium + copper sulfate → magnesium sulfate + copper. The blue colour fades and brown copper forms.
- No reaction happens if the metal is less reactive than the metal in the compound, for example copper + zinc sulfate.
Extracting metals
- Unreactive metals such as gold are found in the Earth as the metal itself. Most metals are found as compounds in ores, and must be extracted by chemical reactions.
- Metals less reactive than carbon, such as iron and zinc, can be extracted from their oxides by reduction with carbon: 2Fe₂O₃ + 3C → 4Fe + 3CO₂.
- Metals more reactive than carbon, such as aluminium, are extracted by electrolysis, which uses much more energy.
Oxidation and reduction in terms of electrons (Higher)
- Oxidation is the loss of electrons; reduction is the gain of electrons (OIL RIG).
- In Mg + Cu²⁺ → Mg²⁺ + Cu, magnesium is oxidised (Mg → Mg²⁺ + 2e⁻) and copper ions are reduced (Cu²⁺ + 2e⁻ → Cu).
- Ionic equations leave out spectator ions, such as the sulfate ions, which don't change.
Key terms
- Reactivity series
- A list of metals in order of how readily they react.
- Oxidation
- The gain of oxygen, or (Higher) the loss of electrons.
- Reduction
- The loss of oxygen, or (Higher) the gain of electrons.
- Displacement reaction
- A reaction in which a more reactive metal takes the place of a less reactive metal in a compound.
- Ore
- A rock containing enough of a metal compound to make extraction worthwhile.
- Extraction
- Removing a metal from its ore.
- Redox reaction
- A reaction in which both oxidation and reduction happen.
- Spectator ion
- An ion that does not change during a reaction.