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Science · 2024 · 3 marks
CBSE 2024 · Region 2 · Set 1 · Q27
It is observed that Calcium on reaction with water floats on its surface. Explain why it happens. Also write a balanced chemical equation for the reaction that occurs. What happens when the aqueous solution of the product of this reaction reacts with Carbon dioxide gas ? Write a balanced chemical equation for the reaction.
Marking-scheme solution
Bubbles of hydrogen gas formed stick to the surface of calcium and make it lighter than water.
\[\mathrm{Ca}(s)+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}\left(\mathrm{aq}+\mathrm{H}_{2}(g)\right.
\]
The solution formed turns milky.
\[\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})+\mathrm{CO}_{2}(\mathrm{~g}) \longrightarrow \mathrm{CaCO}_{3}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})
\]
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CBSE Class 10 Science past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.