Q.2 (A)(i) Give scientific reasons : When the gas formed on heating limestone, is passed through freshly prepared lime water, the lime water turns milky.
Best answer
Answer: Heating limestone gives carbon dioxide, which reacts with lime water to form insoluble calcium carbonate.
On heating, limestone decomposes: \(\mathrm{CaCO_3 \xrightarrow{\Delta} CaO + CO_2\uparrow}\). When this CO2 is passed through freshly prepared lime water (calcium hydroxide solution), it forms a white precipitate of calcium carbonate, which makes the liquid look milky:
\[\mathrm{Ca(OH)_2 + CO_2 \rightarrow CaCO_3\downarrow + H_2O}\]
This is the standard test for carbon dioxide.
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