State the order of the reactivity series: potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold.
Imagine each metal as a rung on a ladder. The higher the rung, the more eager the metal is to give up its electrons and react. Potassium sits at the top, ready to jump off the ladder, while gold sits at the bottom, very calm and reluctant to react. This ladder helps us predict which metal will displace another in a reaction.
| Rank | Metal |
|---|---|
| 1 | Potassium (K) |
| 2 | Sodium (Na) |
| 3 | Calcium (Ca) |
| 4 | Magnesium (Mg) |
| 5 | Aluminium (Al) |
| 6 | Carbon (C) |
| 7 | Zinc (Zn) |
| 8 | Iron (Fe) |
| 9 | Hydrogen (H) |
| 10 | Copper (Cu) |
| 11 | Silver (Ag) |
| 12 | Gold (Au) |
Tip 1: When a metal reacts with an acid, the metal that sits higher on the ladder will displace hydrogen. Example: \$\displaystyle \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}2 + \text{H}2\$ (works) but \$\displaystyle \text{Cu} + 2\text{HCl} \nrightarrow\$ (does not work).
Tip 2: For displacement reactions between two metals, the metal higher on the ladder will replace the lower one in a solution.
Tip 3: Remember that carbon, while not a metal, is placed in the series because it can displace metals like zinc from their salts.
Which metal will displace iron from a solution of iron(III) chloride? Use the reactivity series to answer.
Answer: Zinc (Zn) will displace iron because it is higher on the ladder.
Potassium (K) – the most reactive metal in the series. It reacts violently with water: \$\displaystyle \text{K} + \text{H}2\text{O} \rightarrow \text{KOH} + \frac{1}{2}\text{H}2\$.
Aluminium is actually more reactive than iron, but it forms a thin oxide layer (\$\text{Al}2\text{O}3\$) that protects it from further reaction, making it appear less reactive in everyday situations.