2.4.2Inorganic Chemistry
Metal Displacement Reactions — Edexcel International GCSE Science Double Award 4SD0 - Chemistry Revision Notes & Topical Questions
5 min read 11 parts Lesson 13 of 52
Part 1 of 5The idea behind the practical
Displacement
- Displacement A more reactive metal displaces a less reactive metal from a solution of its compound.
- If a metal is added to a solution of a more reactive metal's compound, nothing happens.
Using it to rank metals
- Using it to rank metals By testing several metals against several solutions, the order of reactivity can be worked out from which reactions occur.
Oxide displacement too
- Oxide displacement too The same principle applies on heating: zinc reduces copper(II) oxide, Zn + CuO → ZnO + Cu,
- and aluminium displaces iron from iron(III) oxide in the thermite reaction.
Part 2 of 5Method
1
Collect small strips of magnesium, zinc, iron and copper, about 1 cm long, and clean them if they look coated.
2
Use a clean dropping pipette to put a few drops of one metal sulfate solution into each dimple in a row of a dimple tile, with a different pipette for each solution to prevent contamination.
3
Add one piece of each metal to a separate dimple in that row.
4
Observe each dimple and record any change, such as a colour change, bubbles, or a new deposit on the metal.
5
Mark a tick if a reaction occurs and a cross if not, and write a dash where the metal matches the solution, since no change can occur.
6
Repeat for each solution; take care not to overfill the dimples.
Part 3 of 5Results grid
| Solution | Zinc | Magnesium | Copper | Iron |
|---|---|---|---|---|
| Zinc sulfate | - | Yes | No | No |
| Magnesium sulfate | No | - | No | No |
| Copper(II) sulfate | Yes | Yes | - | Yes |
| Iron(II) sulfate | Yes | Yes | No | - |
Part 4 of 5Interpreting the results
1Count the reactions
- Count the reactions Magnesium displaces every other metal in the table, so it is the most reactive.
2Next metals
- Next metals Zinc displaces both iron and copper; iron displaces only copper.
3Least reactive
- Least reactive Copper displaces none of the others, so it is the least reactive.
4Order
- Order Magnesium, then zinc, then iron, then copper, from most to least reactive.
Part 5 of 5Equations for reactions that occur
Magnesium reactions
- Magnesium reactions Mg + ZnSO4 → MgSO4 + Zn
- Mg + CuSO4 → MgSO4 + Cu
- Mg + FeSO4 → MgSO4 + Fe
Zinc and iron reactions
- Zinc and iron reactions Zn + CuSO4 → ZnSO4 + Cu
- Fe + CuSO4 → FeSO4 + Cu, with the blue solution fading and a brown-pink copper deposit forming.
Naming products
- Naming products Iron and copper(II) sulfate form iron(II) sulfate and copper;
- the formula of copper(II) sulfate is CuSO4.
Key terms
| Term | Meaning |
|---|---|
| Displacement reaction | A reaction in which a more reactive metal replaces a less reactive metal in a compound. |
| Reactivity series | A list of metals in order of reactivity. |
| Dimple tile | A tile with small wells for carrying out many tiny reactions. |
| Contamination | Unwanted mixing of substances that spoils the results. |
| Reducing agent | A substance that removes oxygen, such as a more reactive metal heated with an oxide. |
Avoid these mistakes
1
Ticking the dimple where the metal and the sulfate contain the same metal — no change can occur there.
2
Ranking by the number of metals that were displaced from the metal itself rather than the number it displaces.
3
Using the same dropping pipette for all solutions, which contaminates them.
4
Predicting a reaction where the added metal is less reactive than the one in solution.
5
Writing the product as an element when it should be a sulfate, such as MgSO4.
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