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Science · 2023 · 3 marks
CBSE 2023 · Region 6 · Set 1 · Q28
(a) A substance 'X' is used as a building material and is insoluble in water. When it reacts with dil. HCl, it produces a gas which turns lime water…
(a)
A substance 'X' is used as a building material and is insoluble in water. When it reacts with dil. HCl, it produces a gas which turns lime water milky.
(i)
Write the chemical name and formula of 'X'.
(ii)
Write chemical equations for the chemical reactions involved in the above statements.
OR
(b)
A metal ' M ' on reacting with dilute acid liberates a gas 'G'. The same metal also liberates gas 'G' when reacts with a base.
(i)
Write the name of gas 'G'.
(ii)
How will you test the presence of this gas ?
(iii)
Write chemical equations for the reactions of the metal with
(1)
an acid and ($\displaystyle 2$) a base.
Marking-scheme solution
(a) (i) Chemical Name : Calcium Carbonate Chemical formula : \(\displaystyle \mathrm{CaCO}_{3}\)
(ii) \(\displaystyle \bullet \mathrm{CaCO}_{3}+2 \mathrm{HCl} \rightarrow \mathrm{CaCl}_{2}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} \uparrow\)
\(\displaystyle \mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{CO}_{2} \rightarrow \mathrm{CaCO}_{3}+\mathrm{H}_{2} \mathrm{O}\)
OR
(b) (i) Hydrogen / \(\displaystyle \mathrm{H}_{2}\)
(ii) The gas burns with a pop sound
(iii) ($\displaystyle 1$) \(\displaystyle 2 \mathrm{HCl}+\mathrm{Zn} \rightarrow \mathrm{ZnCl}_{2}+\mathrm{H}_{2}\)
(2) \(\displaystyle 2 \mathrm{NaOH}+\mathrm{Zn} \rightarrow \mathrm{Na}_{2} \mathrm{ZnO}_{2}+\mathrm{H}_{2}\)
CBSE Class 10 Science past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.