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Write chemical formula of… (Class 10 Science 2025, Q27)

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ScienceCBSE Class 10 · Board exam 2025, set 31/5/1 · 3 marks · Short answer

CBSE Class 10 Science 2025: question 27

Set in the CBSE Class 10 board exam of 2025, paper 31/5/1, section C, question 27, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q27 · 3 marks · Short answerAcids, Bases and Salts

Write chemical formula of washing soda. How is it obtained from baking soda? List two uses of washing soda.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/5/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Washing soda is a hydrated salt with ten water molecules.

Hint 2

What does sodium hydrogencarbonate turn into when heated? Then add water of crystallisation.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Chemical formula of washing soda: (sodium carbonate decahydrate).

    1 mark

  2. Heating baking soda gives sodium carbonate: . Recrystallising this sodium carbonate from water gives washing soda: .

    1 mark

  3. Uses (any two): (i) in the glass, soap and paper industries; (ii) for removing permanent hardness of water; (iii) as a cleaning agent for domestic purposes; (iv) in the manufacture of borax.

    1 mark

Answer: Na₂CO₃·10H₂O; heat baking soda to get Na₂CO₃, then recrystallise; uses: glass/soap/paper industry, removing permanent hardness of water.

Where the marks are

  • Correct formula Na₂CO₃·10H₂O (1 mark)
  • Heating NaHCO₃ to Na₂CO₃ followed by recrystallisation, with equations (1 mark)
  • Any two correct uses (½ + ½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Acids, Bases and Salts, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 31/5/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.