Displacement evidence: build a consistent metal order
| English | 中文 | Pinyin |
|---|---|---|
| displacement reaction/dɪˈspleɪsmənt rɪˈækʃn/ | 置换反应 | zhì huàn fǎn yìng |
| comparison control | 比较对照 | bǐ jiào duì zhào |
What would explain this observation?
- Iron in copper(II) sulfate solution can acquire a copper coating. The more reactive metal takes the place of the less reactive metal in the compound.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- A more reactive metal displaces a less reactive metal from a compound. Fe + CuSO₄ → FeSO₄ + Cu shows iron replacing copper, so the evidence supports Fe>Cu. Copper placed in iron(II) sulfate does not displace iron under the same ordinary comparison. Displacement is a chemical change producing different substances, not simply dissolving a solid.
- displacement reaction 置换反应: A reaction in which a more reactive element replaces a less reactive element in a compound; comparison control 比较对照: A comparison used to identify whether the intended treatment caused a change.
Zinc displaces iron, and iron displaces copper. Which order fits?
For supplied results, translate each successful displacement into a comparison arrow: A displaces B implies A>B. Combine comparisons into an order and check for contradictions. If A displaces B and B displaces C, A>B>C is consistent. Lack of visible reaction alone needs care because an unsuitable method, protective layer or short observation time can hide a reaction.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- For supplied results, translate each successful displacement into a comparison arrow: A displaces B implies A>B. Combine comparisons into an order and check for contradictions. If A displaces B and B displaces C, A>B>C is consistent. Lack of visible reaction alone needs care because an unsuitable method, protective layer or short observation time can hide a reaction.
- Use approved dilute salt solutions, clean matched metal samples, fixed volumes and comparable observation times. Record colour, deposit and sample changes without assigning identity from colour alone. A control with no added metal helps distinguish background change. Dispose of metal-containing solutions through the school’s specified collection route; do not test highly reactive metals in water-based salt solutions independently.
Which two habits make the investigation or model in this case more defensible?
Use approved dilute salt solutions, clean matched metal samples, fixed volumes and comparable observation times. Record colour, deposit and sample changes without assigning identity from colour alone. A control with no added metal helps distinguish background change. Dispose of metal-containing solutions through the school’s specified collection route; do not test highly reactive metals in water-based salt solutions 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: supplied results show zinc displaces iron and copper, and iron displaces copper. The consistent order is Zn>Fe>Cu. If 8.0 g of a supplied recoverable-metal model gives 6.4 g recovered deposit, recovery is 6.4/8.0×100=80%. That recovery calculation does not determine the reactivity order; the displacement comparisons do.
A supplied deposit model could give 15 g metal; 12 g is recovered. Find percentage recovery. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A supplied deposit model could give 15 g metal; 12 g is recovered. Find percentage recovery.
The result is 80 %. Known: supplied results show zinc displaces iron and copper, and iron displaces copper. The consistent order is Zn>Fe>Cu. If 8.0 g of a supplied recoverable-metal model gives 6.4 g recovered deposit, recovery is 6.4/8.0×100=80%. That recovery calculation does not determine the reactivity order; the displacement comparisons do.
Check the conclusion and its limits
- A metal cannot normally displace itself to produce a net change. Do not call the solution deposit the newly formed more reactive metal. Half and ionic equations belong to the separate HT treatment; the common-tier displacement conclusion can be explained using compounds and the series.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Copper normally displaces iron from iron(II) sulfate because copper is below iron in the series. This claim is false: A metal cannot normally displace itself to produce a net change. Do not call the solution deposit the newly formed more reactive metal. Half and ionic equations belong to the separate HT treatment; the common-tier displacement conclusion can be explained using compounds and the series.
Displacement evidence: build a consistent metal order: For supplied results, translate each successful displacement into a comparison arrow: A displaces B implies A>B. Combine comparisons into an order and check for contradictions. If A displaces B and B displaces C, A>B>C is consistent. Lack of visible reaction alone needs care because an unsuitable method, protective layer or short observation time can hide a reaction.
Copper normally displaces iron from iron(II) sulfate because copper is below iron in the series.
A metal cannot normally displace itself to produce a net change. Do not call the solution deposit the newly formed more reactive metal. Half and ionic equations belong to the separate HT treatment; the common-tier displacement conclusion can be explained using compounds and the series.
A reaction in which a more reactive element replaces a less reactive element in a compound: write the technical term.
displacement reaction means A reaction in which a more reactive element replaces a less reactive element in a compound.