Using a set of experimental observations, deduce the order of reactivity of the following metals: Li, Na, K, Ca, Mg, Al, Zn, Fe, Cu, Ag, Au.
Think of it as a super‑hero ranking – the most powerful heroes (metals) are at the top. In chemistry, the most reactive metals are at the top because they give up electrons the easiest.
When a metal reacts with another substance, it usually loses electrons to form a positive ion:
\$M \rightarrow M^{n+} + ne^-\$
Metals higher in the series can displace those below it from their compounds.
| Metal | Reaction with 1 M HCl | Reaction with Water (25 °C) | Reaction with CuSO₄ (aq) |
|---|---|---|---|
| Li | ⚡️ vigorous, \$2\text{Li} + 2\text{HCl} \rightarrow 2\text{LiCl} + \text{H}_2\$ | ⚡️ vigorous, \$2\text{Li} + 2\text{H}2\text{O} \rightarrow 2\text{LiOH} + \text{H}2\$ | ?? displaces Cu (blue solution turns colourless) |
| Na | ⚡️ vigorous, \$2\text{Na} + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{H}_2\$ | ⚡️ vigorous, \$2\text{Na} + 2\text{H}2\text{O} \rightarrow 2\text{NaOH} + \text{H}2\$ | ?? displaces Cu |
| K | ⚡️ very vigorous, \$2\text{K} + 2\text{HCl} \rightarrow 2\text{KCl} + \text{H}_2\$ | ⚡️ very vigorous, \$2\text{K} + 2\text{H}2\text{O} \rightarrow 2\text{KOH} + \text{H}2\$ | ?? displaces Cu |
| Ca | ⚡️ vigorous, \$Ca + 2\text{HCl} \rightarrow \text{CaCl}2 + \text{H}2\$ | ⚡️ moderate, \$Ca + 2\text{H}2\text{O} \rightarrow \text{Ca(OH)}2 + \text{H}_2\$ | ?? displaces Cu |
| Mg | ⚡️ moderate, \$Mg + 2\text{HCl} \rightarrow \text{MgCl}2 + \text{H}2\$ | ⚡️ slow, \$Mg + 2\text{H}2\text{O} \rightarrow \text{Mg(OH)}2 + \text{H}_2\$ (only at 100 °C) | ?? displaces Cu |
| Al | ⚡️ moderate, \$Al + 2\text{HCl} \rightarrow \text{AlCl}3 + \text{H}2\$ | ⚡️ very slow, surface film blocks reaction | ?? displaces Cu |
| Zn | ⚡️ moderate, \$Zn + 2\text{HCl} \rightarrow \text{ZnCl}2 + \text{H}2\$ | ⚡️ very slow, no reaction at 25 °C | ?? displaces Cu |
| Fe | ⚡️ slow, \$Fe + 2\text{HCl} \rightarrow \text{FeCl}2 + \text{H}2\$ | ⚡️ very slow, no reaction at 25 °C | ?? displaces Cu |
| Cu | ⚡️ very slow, \$Cu + 2\text{HCl} \rightarrow \text{CuCl}2 + \text{H}2\$ (only at 100 °C) | ⚡️ no reaction with water | ❌ does not displace Cu from CuSO₄ (same metal) |
| Ag | ⚡️ very slow, \$Ag + 2\text{HCl} \rightarrow \text{AgCl} + \text{H}_2\$ (only at 100 °C) | ⚡️ no reaction with water | ❌ does not displace Cu from CuSO₄ |
| Au | ⚡️ no reaction with HCl | ⚡️ no reaction with water | ❌ does not displace Cu from CuSO₄ |
K > Na > Li > Ca > Mg > Al > Zn > Fe > Cu > Ag > Au
🔍 Why this order? Potassium, sodium, and lithium are the most reactive alkali metals – they give off hydrogen gas instantly. Calcium and magnesium are alkaline earth metals, slightly less reactive. Aluminum is a post‑transition metal that can displace copper but is protected by a thin oxide film. Zinc and iron are transition metals that can displace copper but not silver or gold. Copper is less reactive than iron but can displace hydrogen from acids. Silver and gold are noble metals – they are at the very bottom.