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Science · 2026 · 3 marks
CBSE 2026 · Region 1 · Set 1 · Q27
(a) Explain chlor-alkali process with chemical equation. Name the products formed at anode and cathode.
(a)
Explain chlor-alkali process with chemical equation. Name the products formed at anode and cathode.
OR
(b)
Write the preparation of following compounds with balanced chemical equation :
(i)
Baking soda
(ii)
Bleaching powder
(iii)
Plaster of Paris
Marking-scheme solution
When electricity is passed through brine, it decomposes to form sodium hydroxide (alkali) and chlorine, hence this process is called chlor-alkali process.
\(\displaystyle 2 \mathrm{NaCl}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \xrightarrow{\text { Electricity }} 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g})\)
At anode: \(\displaystyle \mathrm{Cl}_{2}\)
At cathode: \(\displaystyle \mathrm{H}_{2}\)
\(\displaystyle \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}+\mathrm{NH}_{3}+\mathrm{CO}_{2} \rightarrow \mathrm{NaHCO}_{3}+\mathrm{NH}_{4} \mathrm{Cl}\)
(ii)
\(\displaystyle \mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{Cl}_{2} \rightarrow \mathrm{CaOCl}_{2}+\mathrm{H}_{2} \mathrm{O}\) /
\(\displaystyle 2 \mathrm{Ca}(\mathrm{OH})_{2}+2 \mathrm{Cl}_{2} \rightarrow \mathrm{Ca}(\mathrm{ClO})_{2}+\mathrm{CaCl}_{2}+2 \mathrm{H}_{2} \mathrm{O}\)
(iii)
\(\displaystyle \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O} \xrightarrow{373 \mathrm{~K}} \mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}+1 \frac{1}{2} \mathrm{H}_{2} \mathrm{O}\)
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CBSE Class 10 Science past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.