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Reactions of Group 2 metals

Your guide: Miss SanaCounts atoms the way you count rupees: carefully.

Reactions of Group 2 metals

A strip of magnesium burns with a dazzling white light. Calcium gives a brick red flame.

Let us see what each metal does with oxygen, water and acids.

Oxygen, water, acids.

1 · With oxygen

All Group 2 metals burn in oxygen. They form metal oxides, MO.

2M + O2 → 2MO

Beryllium reacts above 600 °C. A thin, strong oxide layer protects it, so it is less reactive.

2Be(s) + O2(g) → 2BeO(s)

Magnesium burns brightly in air. Calcium reacts more vigorously and gives a brick red flame.

The oxides are white solids and basic. The basic character grows down the group.

The oxide ion reacts with water and makes OH−. That is why the solution is basic.

O2− + H2O → 2OH−

2 · With water

Beryllium does not react with water or steam, even when heated. Its oxide layer protects it.

The other metals make a hydroxide M(OH)2 and hydrogen.

Magnesium with cold water is very slow:

Mg(s) + 2H2O(l) → Mg(OH)2(aq) + H2(g)

With steam it is faster and makes magnesium oxide:

Mg(s) + H2O(g) → MgO(s) + H2(g)

Calcium reacts more vigorously. Calcium hydroxide is sparingly soluble and forms a white precipitate.

Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)

The hydroxides are less basic than Group 1 hydroxides. They get more basic down the group, as solubility grows.

3 · With dilute acids

Group 2 metals react with dilute acids. They give a salt and hydrogen.

M(s) + 2HCl(aq) → MCl2(aq) + H2(g)

Reactivity increases down the group. Beryllium also reacts, but its oxide layer can slow the reaction.

Magnesium reacts readily with hydrochloric and sulphuric acid:

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g)

Calcium reacts vigorously with hydrochloric acid:

Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g)

With sulphuric acid the reaction can stop early. Calcium sulphate is sparingly soluble and coats the metal.

Ca(s) + H2SO4(aq) → CaSO4(s) + H2(g)

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Notes, short questions and MCQs

Read the full notes: key terms, model answers and MCQs with answers

Reactions of Group 2 metals

A strip of magnesium burns with a dazzling white light. Calcium gives a brick red flame.

Let us see what each metal does with oxygen, water and acids.

Oxygen, water, acids.

1 · With oxygen

All Group 2 metals burn in oxygen. They form metal oxides, MO.

2M + O2 → 2MO

Beryllium reacts above 600 °C. A thin, strong oxide layer protects it, so it is less reactive.

2Be(s) + O2(g) → 2BeO(s)

Magnesium burns brightly in air. Calcium reacts more vigorously and gives a brick red flame.

The oxides are white solids and basic. The basic character grows down the group.

The oxide ion reacts with water and makes OH−. That is why the solution is basic.

O2− + H2O → 2OH−

2 · With water

Beryllium does not react with water or steam, even when heated. Its oxide layer protects it.

The other metals make a hydroxide M(OH)2 and hydrogen.

Magnesium with cold water is very slow:

Mg(s) + 2H2O(l) → Mg(OH)2(aq) + H2(g)

With steam it is faster and makes magnesium oxide:

Mg(s) + H2O(g) → MgO(s) + H2(g)

Calcium reacts more vigorously. Calcium hydroxide is sparingly soluble and forms a white precipitate.

Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)

The hydroxides are less basic than Group 1 hydroxides. They get more basic down the group, as solubility grows.

3 · With dilute acids

Group 2 metals react with dilute acids. They give a salt and hydrogen.

M(s) + 2HCl(aq) → MCl2(aq) + H2(g)

Reactivity increases down the group. Beryllium also reacts, but its oxide layer can slow the reaction.

Magnesium reacts readily with hydrochloric and sulphuric acid:

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g)

Calcium reacts vigorously with hydrochloric acid:

Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g)

With sulphuric acid the reaction can stop early. Calcium sulphate is sparingly soluble and coats the metal.

Ca(s) + H2SO4(aq) → CaSO4(s) + H2(g)

Key terms

Basic oxide
An oxide that makes OH− in water.
Protective oxide layer
A thin layer that stops a metal reacting further.
Sparingly soluble
Dissolves only a little in water.
Precipitate
A solid that forms in a solution.

Short questions with model answers

  1. Q1. Quick Check 17.1 (a): write equations for X, (ii) Ba with water.

      (i) 2Ca(s) + O2(g) → 2CaO(s) (ii) Ba(s) + 2H2O(l) → Ba(OH)2(aq) + H2(g) (Both follow the book's general patterns.)

    • Q2. Quick Check 17.1 (d): write balanced equations for calcium and barium burning in air. Compare their reactivity.

        2Ca(s) + O2(g) → 2CaO(s) 2Ba(s) + O2(g) → 2BaO(s) Barium is below calcium, so it is more reactive.

      • Q3. Quick Check 17.1 (b): predict the reactions of Sr and Ba with sulphuric acid.

          Calcium sulphate is sparingly soluble and stops the reaction early. Strontium and barium sulphates are even less soluble (Table 17.4). So the reaction should stop early or be very slight. (Prediction from the book data. The book gives no answer.)

        Common mistakes

        • ✗ “Beryllium does not react with acids.”

          ✓ It does react. Its oxide layer only slows the reaction.

        • ✗ “Magnesium gives hydroxide with steam.”

          ✓ With steam it gives the oxide MgO. With cold water it gives Mg(OH)2.

        • ✗ “All Group 2 metals react with water.”

          ✓ Not beryllium. It does not react with water or steam.

        MCQs

        1. 1. Magnesium reacts with steam to give:

          1. (a) MgO and H2
          2. (b) Mg(OH)2 and H2
          3. (c) Mg(OH)2 only
          4. (d) MgO and H2O
          Show answer

          (a) Mg + H2O → MgO + H2.

        2. 2. Which Group 2 metal does not react with water or steam?

          1. (a) Beryllium
          2. (b) Magnesium
          3. (c) Calcium
          4. (d) All of them react
          Show answer

          (a) Its protective oxide layer stops the reaction.

        3. 3. Calcium burning in oxygen gives a flame that is:

          1. (a) brick red
          2. (b) golden yellow
          3. (c) green
          4. (d) blue
          Show answer

          (a) The book says brick red flame.

        4. 4. Why can calcium and sulphuric acid stop reacting early?

          1. (a) CaSO4 is sparingly soluble and coats the metal
          2. (b) CaSO4 is a gas
          3. (c) Calcium is unreactive
          4. (d) The acid is too strong
          Show answer

          (a) A protective layer of solid forms.

        Quick revision

        • Metals plus oxygen give white basic oxides MO.
        • All except beryllium react with water. Mg with steam gives MgO.
        • With acids: salt plus hydrogen. Reactivity grows down the group.

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