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Science · 2024 · 5 marks
CBSE 2024 · Region 5 · Set 1 · Q34
(a) A few crystals of ferrous sulphate were taken in a dry boiling tube and heated. Tiny water droplets were observed in the tube after some time.…
A few crystals of ferrous sulphate were taken in a dry boiling tube and heated. Tiny water droplets were observed in the tube after some time.
(i)
From where did these water droplets appear ? Explain.
(ii)
What colour change will be observed during heating ?
(iii)
How many molecules of water are attached per molecule of $\displaystyle \mathrm{FeSO}_{4}$ crystal ? Write the molecular formula of crystalline forms of (I) Copper sulphate, and (II) Sodium carbonate.
(iv)
State how is Plaster of Paris obtained from gypsum. Write two uses of Plaster of Paris.
An acid 'X' present in tamarind when mixed with 'Y', produces a mixture 'Z'. 'Z' on addition to a dough when heated makes cakes soft and spongy. 'Y' is prepared from common salt and helps in faster cooking.
(i)
Write the common names of 'X', 'Y' and 'Z', and the chemical formula of 'Y'.
(ii)
How is 'Y' prepared and how does it help in making cakes soft and spongy ? Illustrate the reaction with suitable chemical equation.
(iii)
Write the name and chemical formula of a mild base other than 'Y' used as an antacid.
Marking-scheme solution
(i) The molecules of water of crystallisation in ferrous sulphate crystals get evaporated on heating.
(ii) Green ⟶ White
(iii) Seven / \(\displaystyle \left(\mathrm{FeSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}\right)\)
(I) \(\displaystyle \mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\)
(II) \(\displaystyle \mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}\)
(iv)
• On heating gypsum \(\displaystyle \left(\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\right)\) at $\displaystyle 373$ K it loses water molecules/ \(\displaystyle \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O} \xrightarrow[373 \mathrm{~K}]{\Delta} \mathrm{CaSO}_{4} \cdot 1 / 2 \mathrm{H}_{2} \mathrm{O}+1 \frac{1}{2} \mathrm{H}_{2} \mathrm{O}\)
Two uses of plaster of Paris:
Making toys / material for decoration
Supporting fractured bones
(ii)
\[\mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2}+\mathrm{NH}_{3} \longrightarrow \mathrm{NH}_{4} \mathrm{Cl}+\mathrm{NaHCO}_{3}
\]
\(\displaystyle \mathrm{NaHCO}_{3}+\mathrm{H}^{+} \longrightarrow \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}+\) Sodium salt of acid
\(\displaystyle \mathrm{CO}_{2}\) released during heating makes the cake soft and spongy
(iii)
Magnesium hydroxide; \(\displaystyle \mathrm{Mg}(\mathrm{OH})_{2}\)
All Acids, Bases and Salts questions2024 question paperNCERT solutions: Acids, Bases and SaltsPractice Acids, Bases and Salts →
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CBSE Class 10 Science past-paper question from the 2024 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.