The reactivity series

The reactivity series ranks metals based on their ability to react with water, acids, and other substances. This ranking helps predict how metals behave in chemical reactions, such as displacement and corrosion resistance.

The reactivity series

The order of metals in the reactivity series is:

(Most reactive)

Potassium

Sodium 

Calcium 

Magnesium 

Aluminium 

Carbon 

Zinc 

Iron 

Hydrogen 

Copper 

Silver 

Gold 

(Least reactive)

• Most Reactive: Potassium, sodium, and calcium, which react vigorously with water.

• Least Reactive: Silver and gold, which do not react with water or acids under normal conditions.

Reactions of metals with water and acids

Reactions with Water

• Potassium, Sodium, and Calcium with Cold Water:

  • React vigorously, producing a metal hydroxide and hydrogen gas.

    • Example: 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) (Potassium reacts explosively with water.)

Reactions with Steam

• Magnesium:

  • Reacts with steam to form magnesium oxide and hydrogen gas.

    • Example: Mg(s) + H₂O(g) → MgO(aq) + H₂(g)

Reactions with Dilute Hydrochloric Acid

• Magnesium, Zinc, and Iron:

  • React with dilute HCl to produce a salt and hydrogen gas.

    • Example: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

  • The rate of reaction decreases as you move down the reactivity series.

• Copper, Silver, and Gold:

  • Do not react with dilute HCl due to their low reactivity.

Reactions of magnesium, zinc and iron with dilute hydrochloric acid

Working out the order

Given experimental data (e.g., rate of gas production, temperature change, or metal displacement), you can infer the relative reactivity of metals.

• Example: If magnesium reacts faster than zinc with dilute HCl, magnesium is higher in the reactivity series.

Displacement reactions

Metals higher in the reactivity series can displace those lower down from their aqueous ions.

• Explanation: Reactive metals more readily lose electrons to form positive ions.

• Example: Zinc displaces copper from copper sulfate solution:

Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

Observations in Displacement Reactions

• Copper Sulfate with Magnesium: Magnesium displaces copper (blue solution fades, red copper forms).

• Copper Sulfate with Zinc: Zinc displaces copper but at a slower rate than magnesium.

Unreactivity of aluminium