What happens when carbon dioxide gas is passed through lime water? Write the chemical equation.
Generated by claude-sonnet-4-6 · 2026-06-17 12:33 · grounding rag
Model Answer
When carbon dioxide gas is passed through lime water, it turns milky due to the formation of white precipitate of calcium carbonate (CaCO₃).
$$\text{Ca(OH)}_2(aq) + \text{CO}_2(g) \rightarrow \text{CaCO}_3(s) + \text{H}_2\text{O}(l)$$
Source: Chapter 1, Section 1.2.1 Combination Reaction
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Explanation
- The key observation (milky appearance) and the reason (CaCO₃ precipitate) must both be stated for full marks.
- Write the balanced chemical equation with correct state symbols — examiners specifically check for (s), (aq), (g), (l).
- This reaction is also the standard test for CO₂ gas — worth mentioning if asked in a broader question.