A Levels Chemistry (9701)•9701/11/M/J/25
Explanation
Thermal decomposition of Group 2 nitrates
Steps:
- Group 2 nitrates decompose on heating to form metal oxide, nitrogen dioxide, and oxygen.
- General formula: 2M(NO₃)₂ → 2MO + 4NO₂ + O₂, where M is the Group 2 metal.
- For radium (Ra), substitute into the formula.
- Balance atoms: left side has 2 Ra, 12 O, 4 N; right side matches with 2 RaO (2 Ra, 2 O), 4 NO₂ (4 N, 8 O), O₂ (2 O).
Why A is correct:
- Matches the standard balanced equation for Group 2 nitrate decomposition, conserving atoms per the law of conservation of mass.
Why the others are wrong:
- B: Unbalanced; uses single molecule but produces half O₂, violating atom conservation.
- C: Produces NO (nitric oxide) instead of NO₂ (nitrogen dioxide), incorrect for strong heating.
- D: Produces 8 NO₂, exceeding nitrogen atoms and unbalancing the equation.
Final answer: A
Topic: Group 2
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