Higher Tier: displacement as electron loss and gain
| English | 中文 | Pinyin |
|---|---|---|
| electron oxidation | 失电子氧化 | shī diàn zi yǎng huà |
| electron reduction | 得电子还原 | dé diàn zi huán yuán |
What would explain this observation?
- Higher Tier: Zinc reacting with copper(II) ions transfers electrons even though the net ionic equation contains no oxygen. The electron definition extends redox beyond oxygen reactions.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Oxidation is loss of electrons; reduction is gain of electrons. Zn → Zn²⁺ + 2e⁻ is oxidation and Cu²⁺ + 2e⁻ → Cu is reduction. Combining gives Zn + Cu²⁺ → Zn²⁺ + Cu. Sulfate ions in a zinc–copper sulfate experiment remain spectator ions and do not appear in this net ionic equation.
- electron oxidation 失电子氧化: Oxidation defined as loss of electrons; electron reduction 得电子还原: Reduction defined as gain of electrons.
In Zn + Cu²⁺ → Zn²⁺ + Cu, which species gains electrons?
Check both atom counts and total charge. The combined left charge is +2 and the right charge is +2. Zinc atoms become positive ions by losing electrons; copper ions become neutral metal atoms by accepting them. Identify the actual species reduced, Cu²⁺, rather than saying the already-neutral copper product gains further electrons.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Check both atom counts and total charge. The combined left charge is +2 and the right charge is +2. Zinc atoms become positive ions by losing electrons; copper ions become neutral metal atoms by accepting them. Identify the actual species reduced, Cu²⁺, rather than saying the already-neutral copper product gains further electrons.
- Write the two half equations, multiply them if needed to make equal electron numbers, then cancel electrons. Cancel only unchanged spectator ions in a full ionic equation. Use the reactivity series to predict whether a proposed displacement is supported; a charge-balanced equation alone does not guarantee that the reaction will occur.
Which two habits make the investigation or model in this case more defensible?
Write the two half equations, multiply them if needed to make equal electron numbers, then cancel electrons. Cancel only unchanged spectator ions in a full ionic equation. Use the reactivity series to predict whether a proposed displacement is supported; a charge-balanced equation alone does not guarantee that the reaction will occur.
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: 2Al → 2Al³⁺ + 6e⁻ and 3Cu²⁺ + 6e⁻ → 3Cu combine as 2Al + 3Cu²⁺ → 2Al³⁺ + 3Cu. Two aluminium atoms supply six electrons and three copper ions accept them. Both sides have charge +6. These particle coefficients are not gram masses.
How many electrons are released when four Al atoms each become Al³⁺? Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
How many electrons are released when four Al atoms each become Al³⁺?
The result is 12 electrons. Known: 2Al → 2Al³⁺ + 6e⁻ and 3Cu²⁺ + 6e⁻ → 3Cu combine as 2Al + 3Cu²⁺ → 2Al³⁺ + 3Cu. Two aluminium atoms supply six electrons and three copper ions accept them. Both sides have charge +6. These particle coefficients are not gram masses.
Check the conclusion and its limits
- Oxidation and reduction occur together in the overall electron transfer. Positive-ion formation by a metal is electron loss, not loss of protons. Electrons cancel from the full reaction but remain useful in each half equation. This entire source section is Higher-only.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A metal forms a positive ion by losing positive protons. This claim is false: Oxidation and reduction occur together in the overall electron transfer. Positive-ion formation by a metal is electron loss, not loss of protons. Electrons cancel from the full reaction but remain useful in each half equation. This entire source section is Higher-only.
Higher Tier: displacement as electron loss and gain: Check both atom counts and total charge. The combined left charge is +2 and the right charge is +2. Zinc atoms become positive ions by losing electrons; copper ions become neutral metal atoms by accepting them. Identify the actual species reduced, Cu²⁺, rather than saying the already-neutral copper product gains further electrons.
A metal forms a positive ion by losing positive protons.
Oxidation and reduction occur together in the overall electron transfer. Positive-ion formation by a metal is electron loss, not loss of protons. Electrons cancel from the full reaction but remain useful in each half equation. This entire source section is Higher-only.
Oxidation defined as loss of electrons: write the technical term.
electron oxidation means Oxidation defined as loss of electrons.