Any metal that is more reactive than copper can displace it from its salt solution. Zinc is a classic example of a metal that readily displaces copper from its salt solutions.
Understanding Metal Reactivity
The ability of one metal to displace another from its salt solution is determined by their relative positions in the activity series (also known as the reactivity series) of metals. A metal higher in the activity series is more reactive; it can more easily lose electrons (oxidize) to form ions, thereby displacing a less reactive metal (which is lower in the series) from its compounds. Conversely, a less reactive metal cannot displace a more reactive metal.
In a displacement reaction, the more reactive metal atom gives up its electrons to the ions of the less reactive metal, causing the less reactive metal ions to gain electrons and form solid metal.
Key Metals That Displace Copper
To displace copper from its salt solution, a metal must be positioned above copper in the activity series. Common metals that fit this criterion include:
- Zinc (Zn)
- Iron (Fe)
- Lead (Pb)
- Magnesium (Mg)
- Aluminum (Al)
- Sodium (Na) (highly reactive; reacts vigorously with water, so typically not used in aqueous solutions for simple displacement demos)
Among these, zinc is a widely recognized and frequently demonstrated example.
Zinc's Displacement of Copper
When a piece of zinc is placed in a blue copper nitrate solution, a clear chemical reaction occurs. The more reactive zinc displaces the less reactive copper from the solution. This process is observed through:
- The formation of solid copper metal, which often appears as a reddish-brown deposit on the surface of the zinc metal.
- The zinc metal dissolving to form colourless Zn²⁺ ions in the solution.
The characteristic blue colour of the copper nitrate solution (due to the presence of Cu²⁺ ions) gradually fades as the copper ions are removed from the solution, eventually becoming colourless if all the copper ions react.
The chemical equation for this reaction is:
Zn(s) + Cu(NO₃)₂(aq) → Zn(NO₃)₂(aq) + Cu(s)
This equation shows that solid zinc reacts with aqueous copper nitrate to produce aqueous zinc nitrate and solid copper.
Simplified Activity Series of Metals
The following table illustrates a portion of the activity series, highlighting metals commonly encountered in displacement reactions, including their reactivity relative to copper:
| Metal | Reactivity Level | Can Displace Copper? | Example Reaction (Conceptual) |
|---|---|---|---|
| Potassium | Very High | Yes | 2K(s) + CuCl₂(aq) → 2KCl(aq) + Cu(s) |
| Sodium | Very High | Yes | 2Na(s) + CuSO₄(aq) → Na₂SO₄(aq) + Cu(s) |
| Calcium | High | Yes | Ca(s) + Cu(NO₃)₂(aq) → Ca(NO₃)₂(aq) + Cu(s) |
| Magnesium | High | Yes | Mg(s) + CuSO₄(aq) → MgSO₄(aq) + Cu(s) |
| Aluminium | High | Yes | 2Al(s) + 3CuCl₂(aq) → 2AlCl₃(aq) + 3Cu(s) |
| Zinc | Moderate | Yes | Zn(s) + Cu(NO₃)₂(aq) → Zn(NO₃)₂(aq) + Cu(s) |
| Iron | Moderate | Yes | Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s) |
| Lead | Moderate | Yes | Pb(s) + CuCl₂(aq) → PbCl₂(aq) + Cu(s) |
| Hydrogen* | Reference Point | No | (Does not displace copper from solution) |
| Copper | Low | N/A | (Cannot displace itself) |
| Silver | Very Low | No | |
| Gold | Very Low | No |
*Note: While hydrogen is a non-metal, it is commonly included as a reference point in the activity series for metals. Metals above hydrogen can displace hydrogen from acids. For a more comprehensive understanding of the activity series, you can refer to resources like Chemistry LibreTexts or BBC Bitesize.
Practical Implications
Understanding metal displacement reactions is fundamental in various scientific and industrial applications:
- Corrosion Prevention: More reactive metals are often used as "sacrificial anodes" to protect less reactive metals from corrosion (e.g., zinc coating on steel in galvanization).
- Metallurgy: This principle is crucial in the extraction of metals from their ores, often involving displacement by a more reactive element.
- Electrochemistry: Displacement reactions are the basis for galvanic cells and certain types of batteries, where chemical energy is converted into electrical energy.
- Environmental Remediation: Displacement can be used to recover valuable metals or remove toxic heavy metal ions like copper from industrial wastewater.
