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Science · 2023 · 2 marks
CBSE 2023 · Region 5 · Set 2 · Q26
(a) On heating 'X' at 373 K, it loses water molecules and becomes 'Y'. 'Y' is a substance which doctors use for supporting fractured bones in the…
(a)
On heating 'X' at $\displaystyle 373$ K, it loses water molecules and becomes 'Y'. 'Y' is a substance which doctors use for supporting fractured bones in the right position.
(i)
Identify 'X' and 'Y'.
(ii)
How can ' X ' be reobtained from ' Y '?
(b)
Two solutions M and N give Red and Blue colour respectively with a universal indicator.
(i)
In which solution will the hydrogen ion concentration be more? Justify your answer.
(ii)
If both M and N solutions are mixed and the resultant mixture is tested with a universal indicator, it turns green. What is the nature of the salt formed ? Justify your answer.
Marking-scheme solution
(i)
$\displaystyle \mathrm{X}=\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O} /$ Gypsum / Calcium sulphate dihydrate
$\displaystyle \mathrm{Y}=\mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O} /$ Plaster of Paris/Calcium sulphate hemi-hydrate
(ii)
$\displaystyle \mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}+1 \frac{1}{2} \mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}$
(i)
M, it is an acidic solution
(ii)
Neutral
M is an acid and N is a base. / Neutralization reaction
SECTION C
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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.