Metal oxides: oxidation gains oxygen, reduction loses it
Diperkenalkan| English | Makna |
|---|---|
| oxidation by oxygen gain/ˌɒksɪˈdeɪʃn baɪ ˈɒksɪdʒn ɡeɪn/ | Oxidation identified as gain of oxygen. |
| reduction by oxygen loss/rɪˈdʌkʃn baɪ ˈɒksɪdʒn lɒs/ | The GCSE definition of reduction as losing oxygen. |
What would explain this observation?
- A strip of magnesium can form a white solid after reacting with oxygen. The new substance contains oxygen as well as the starting metal.
Build the model
- Metals react with oxygen to form metal oxides.
- In the oxygen definition, oxidation is gain of oxygen and reduction is loss of oxygen.
- Magnesium is oxidised in 2Mg + O₂ → 2MgO.
- A metal oxide can be reduced if oxygen is removed from it.
- These definitions identify changes in substances, not merely a change in colour or measured temperature.
- oxidation by oxygen gain 得氧氧化: Oxidation identified as gain of oxygen.
- reduction by oxygen loss 失氧还原: Reduction identified as loss of oxygen.
In 2CuO + C → 2Cu + CO₂, which substance is reduced?
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Reduction is loss of oxygen: CuO loses its oxygen and becomes Cu, so copper oxide is reduced. Carbon GAINS oxygen, so carbon is oxidised - the two always happen together.
Match each technical term to its precise meaning.
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Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- For 2CuO + C → 2Cu + CO₂, copper oxide loses oxygen and is reduced, while carbon gains oxygen and is oxidised.
- The same oxygen atoms leave the oxide and appear in carbon dioxide.
- The two changes occur together in this reaction.
- Oxygen is an element; oxide is a compound containing oxygen with another element, so the names are not interchangeable.
In the lab: Use atom models or supplied before/after formulae to trace oxygen. Balance each element and identify the substance receiving or losing oxygen. Actual burning-metal or heated-oxide work needs the teacher-approved method, heat protection and ventilation. A bright magnesium flame must not be viewed directly; a written example is not an instruction to ignite a sample independently.
Which two habits make the investigation or model in this case more defensible?
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Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a stated metal sample begins at 3.6 g and forms 6.0 g oxide with complete reaction and no losses.
- Oxygen incorporated=6.0−3.6=2.4 g.
- The metal’s gain of oxygen identifies oxidation.
- The oxide mass includes material from the surrounding oxygen, so this is compatible with mass conservation.
Your turn: A metal starts at 4.5 g and gives 7.5 g oxide without losses. Find oxygen mass gained.
A metal starts at 4.5 g and gives 7.5 g oxide without losses. Find oxygen mass gained.
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The result is 3 g. Known: metal 4.5 g; oxide 7.5 g; no losses. Oxygen gained = 7.5 - 4.5 = 3 g. The oxide's extra mass is exactly the oxygen taken from the surroundings.
Check the conclusion and its limits
- Reduction does not mean every mass decreases, and oxidation does not mean every colour change.
- The common-tier oxygen account is distinct from the wider electron definition taught in the separate HT lesson.
- Some redox changes involve no oxygen and therefore need that other definition.
Not true: Oxidation by oxygen gain means loss of oxygen. GAINING oxygen is oxidation; LOSING oxygen is reduction. The definitions are opposite - magnesium gaining oxygen to form MgO is oxidised, while the oxygen it took leaves something else reduced.
- Metals react with oxygen to form metal oxides.
- For 2CuO + C → 2Cu + CO₂, copper oxide loses oxygen and is reduced, while carbon gains oxygen and is oxidised.
- Watch for: reduction does not mean every mass decreases, and oxidation does not mean every colour change.
GAINING oxygen is oxidation; LOSING oxygen is reduction.
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True. GAINING oxygen is oxidation; LOSING oxygen is reduction. The definitions are opposite - magnesium gaining oxygen to form MgO is oxidised, while the oxygen it took leaves something else reduced.
Oxidation identified as gain of oxygen: write the technical term.
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oxidation by oxygen gain means Oxidation identified as gain of oxygen.