A Levels Chemistry (9701)•9701/11/O/N/20
Explanation
Precipitate Formation in Reactions
Steps:
- First mixture: Calcium reacts with water to form calcium hydroxide (white solid) and hydrogen gas.
- Second mixture: Calcium carbonate dissolves in hydrochloric acid, producing soluble calcium chloride, water, and carbon dioxide gas; no solid forms.
- Third mixture: Magnesium sulfate and barium nitrate undergo double displacement, yielding insoluble barium sulfate (white solid) and soluble magnesium nitrate.
- Total white solids: Two mixtures (first and third).
Why C is correct:
- Exactly two mixtures produce white solids, as Ca(OH)₂ and BaSO₄ are insoluble white precipitates per solubility rules.
Why the others are wrong:
- A: Fails to account for the two white solids formed.
- B: Misses the second white solid (BaSO₄).
- D: Includes the second mixture, which produces no solid.
Final answer: C
Topic: Group 2
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