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AQA A-Level Chemistry 3.2.2: Group 2, The Alkaline Earth Metals – Full Spec Summary Sheet

1. Trends in Physical Properties (Mg–Ba)

Atomic Radius:

  • Increases down the group.

  • More electron shells added.

  • Greater distance between nucleus and outer electrons.

First Ionisation Energy:

  • Decreases down the group.

  • Increased atomic radius and shielding.

  • Weaker attraction between nucleus and outermost electron.

Melting Points:

  • Generally decrease down the group (with some exceptions).

  • Group 2 elements are metallic (giant lattice of positive ions in a sea of delocalised electrons).

  • Down the group, metal ions become larger → same charge spread over larger area → weaker metallic bonding.

2. Reactions with Water (Mg–Ba)

General Reaction:

  • M(s) + 2H₂O(l) → M(OH)₂(aq) + H₂(g)

Reactivity Trend:

  • Increases down the group.

  • Observations become more vigorous from Mg → Ba.

Magnesium:

  • Reacts slowly with cold water.

  • Reacts faster with steam:

    • Mg(s) + H₂O(g) → MgO(s) + H₂(g)

Barium:

  • Reacts rapidly with cold water.

3. Extraction of Titanium Using Magnesium

Process:

  • TiCl₄(g) + 2Mg(l) → Ti(s) + 2MgCl₂(l)

  • Magnesium is used as a reducing agent to extract titanium from its chloride.

4. Solubility of Hydroxides (Mg(OH)₂ – Ba(OH)₂)

Trend:

  • Solubility increases down the group.

Examples:

  • Mg(OH)₂: Sparingly soluble.

  • Ba(OH)₂: Very soluble → forms strongly alkaline solution.

Uses:

  • Mg(OH)₂: Used in medicine as antacid to neutralise stomach acid.

  • Ca(OH)₂: Used in agriculture to neutralise acidic soils.

5. Solubility of Sulfates (MgSO₄ – BaSO₄)

Trend:

  • Solubility decreases down the group.

Examples:

  • MgSO₄: Soluble.

  • BaSO₄: Insoluble.

Uses of BaSO₄:

  • Used in medicine as a barium meal for X-rays.

  • Safe because BaSO₄ is insoluble → doesn’t release toxic Ba²⁺ ions.

6. Test for Sulfate Ions (SO₄²⁻)

Reagents:

  • Use acidified barium chloride solution: BaCl₂ + HCl

Reaction:

  • Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)

  • White precipitate indicates presence of sulfate ions.

Why Acidified?:

  • HCl added to remove carbonate ions (which would also form white precipitate with Ba²⁺).

  • Prevents false positive result.

End of Summary