Metal oxides: oxidation gains oxygen, reduction loses it
| English | Français |
|---|---|
| oxidation by oxygen | oxidation by oxygen |
| reduction by oxygen | reduction by 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.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
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 得氧氧化: Oxidation identified as gain of oxygen; reduction by oxygen 失氧还原: Reduction identified as loss of oxygen.
In 2CuO + C → 2Cu + CO₂, which substance is reduced?
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.
Match each technical term to its precise meaning.
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.
- 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?
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.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- 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.
A metal starts at 4.5 g and gives 7.5 g oxide without losses. Find oxygen mass gained. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A metal starts at 4.5 g and gives 7.5 g oxide without losses. Find oxygen mass gained.
The result is 3 g. 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.
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.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Oxidation by oxygen means loss of oxygen. This claim is false: 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.
Metal oxides: oxidation gains oxygen, reduction loses 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.
Oxidation by oxygen means loss of oxygen.
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.
Oxidation identified as gain of oxygen: write the technical term.
oxidation by oxygen means Oxidation identified as gain of oxygen.