Experiment: Carbon dioxide was passed through limewater and then in excess.Observation: Limewater turned milky, then became clear again.Question: What does this show?
Correct answer: D. Initially, carbon dioxide reacts with limewater to form insoluble calcium carbonate, which causes the milkiness. When excess CO₂ is added, the calcium carbonate dissolves to form soluble calcium hydrogen carbonate, making the solution clear again.
- A. Calcium carbonate is a white, insoluble solid that forms when carbon dioxide reacts with limewater, not colored or volatile.
- B. The milkiness observed is due to the formation of calcium carbonate, not related to oxygen content. This option misinterprets the observation.
- C. CO₂ does react with limewater to form calcium carbonate, leading to the initial milkiness observed in the experiment.
- D. Initially, carbon dioxide reacts with limewater to form insoluble calcium carbonate, which causes the milkiness. When excess CO₂ is added, the calcium carbonate dissolves to form soluble calcium hydrogen carbonate, making the solution clear again.
Explanation
When carbon dioxide reacts with limewater (calcium hydroxide), it forms calcium carbonate, which is initially insoluble and causes the milkiness. With excess CO₂, the calcium carbonate then dissolves to form soluble calcium hydrogen carbonate, resulting in a clear solution again. The correct answer explains this chemical reaction sequence accurately. Options A, C, and D provide incorrect interpretations or associations that do not align with the experimental observations.
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About Scientific Reasoning
Scientific reasoning evaluates hypotheses through observations, variables, controls, measurements and experimental results. Questions involve identifying independent and dependent variables, recognising a fair test, interpreting tables or graphs, distinguishing evidence from opinion, and deciding whether data supports, rejects or leaves a hypothesis unresolved.
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