Topic 10: Group 2

Question 1

Definitions I:
(a) Thermal stability
(b) Metallic bonding
(c) Solubility trend

Answer 1

Definitions I:
(a) Resistance of a compound to decomposition by heat.
(b) Electrostatic attraction between metal ions and delocalised electrons.
(c) Change in solubility of Group 2 compounds, e.g., sulfates decrease down group.

Question 2

Write equations for:
(a) Mg reacting with H₂O [1 Mark]
(b) Ba reacting with HCl [1 Mark]

Answer 2

(a) Mg + H₂O → MgO + H₂ (slow, needs heat) (1 mark)
(b) Ba + 2HCl → BaCl₂ + H₂ (1 mark)

Question 3

Write equations for MgO and BaCO₃ reacting with dilute H₂SO₄. [2 Marks]

Answer 3

MgO + H₂SO₄ → MgSO₄ + H₂O (1 mark)
BaCO₃ + H₂SO₄ → BaSO₄ + H₂O + CO₂ (1 mark)

Question 4

How does thermal stability of Group 2 nitrates change from Mg to Ba, and why? [3 Marks]

Answer 4

Increases Mg to Ba, larger cations stabilise anion (1 mark)
Less polarisation of NO₃⁻ down group (1 mark)
e.g., Ba(NO₃)₂ needs higher temperature (1 mark)

Question 5

Why does Ba react faster with water than Mg, despite both being in Group 2? [2 Marks]

Answer 5

Ba larger, lower charge density (1 mark)
Weaker metallic bonding, more reactive (1 mark)

Question 6

Write equations for the thermal decomposition of:
(a) MgCO₃ [1 Mark]
(b) Ca(NO₃)₂ [1 Mark]

Answer 6

(a) MgCO₃ → MgO + CO₂ (1 mark)
(b) Ca(NO₃)₂ → CaO + 2NO₂ + ½O₂ (1 mark)

Question 7

Predict the solubility of Mg(OH)₂ vs. BaSO₄ in water. [2 Marks]

Answer 7

Mg(OH)₂ less soluble, hydroxides increase down (1 mark)
BaSO₄ insoluble, sulfates decrease down (1 mark)

Question 8

In a lab, Mg burns in O₂ to form MgO. Write the equation and explain its high melting point. [2 Marks]

Answer 8

2Mg + O₂ → 2MgO (1 mark)
High melting due to strong ionic lattice (1 mark)

Question 9

How do Mg(OH)₂ and Ba(OH)₂ react with HCl, and what products form? [2 Marks]

Answer 9

Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O (1 mark)
Ba(OH)₂ + 2HCl → BaCl₂ + 2H₂O (1 mark)

Question 10

Why does CaCO₃ decompose at a higher temperature than MgCO₃? [2 Marks]

Answer 10

Ca²⁺ larger, less polarising than Mg²⁺ (1 mark)
CO₃²⁻ more stable, higher decomposition temp (1 mark)

Question 11

Describe the trend in reactivity of Group 2 metals with dilute acids from Mg to Ba. [3 Marks]

Answer 11

Reactivity increases Mg to Ba (1 mark)
Larger atoms, lower ionisation energy (1 mark)
Faster H₂ production with HCl (1 mark)

Question 12

Predict the products when Sr(OH)₂ reacts with HNO₃ based on Group 2 trends. [2 Marks]

Answer 12

Sr(OH)₂ + 2HNO₃ → Sr(NO₃)₂ + 2H₂O (1 mark)
Similar to Ca, Ba due to Group 2 trends (1 mark)