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Answer the following. (Science 2023 31/4/1 Q28)

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ScienceCBSE Class 10 · Board exam 2023, set 31/4/1 · 3 marks · Short answer

CBSE Class 10 Science 2023: question 28

Set in the CBSE Class 10 board exam of 2023, paper 31/4/1, section C, question 28, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q28 · 3 marks · Short answerAcids, Bases and Salts

Answer the following.

  1. (i)

    Suggest a safe procedure of diluting a strong concentrated acid.

    1 mark
  2. (ii)

    Name the salt formed when sulphuric acid is added to sodium hydroxide and write its pH.

    1 mark
  3. (iii)

    Dry HCl gas does not change the colour of dry blue litmus paper. Why ?

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/4/1.

Hints

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

Hint 1

Dilution of a concentrated acid releases a lot of heat. Which way round is safer?

Hint 2

Neutralisation of a strong acid by a strong base gives which kind of solution?

Hint 3

What must be present for HCl to produce ions?

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. (i) Always add the concentrated acid slowly to water, never water to acid, with constant stirring. The process is highly exothermic. Adding water to acid can make the mixture splash and the glass break.

    1 mark

  2. (ii)
    The salt formed is **sodium sulphate, **.

    ½ mark

  3. It is a salt of a strong acid and a strong base, so its solution is neutral with pH = 7.

    ½ mark

  4. (iii) Dry HCl gas does not ionise in the absence of water, so no (hydronium) ions are formed. Acidic behaviour needs ions, so dry blue litmus does not turn red.

    1 mark

Answer: (i) Add acid slowly to water with stirring; (ii) Sodium sulphate, pH 7; (iii) No H⁺ ions form without water

Where the marks are

  • Acid added slowly to water with constant stirring (1 mark)
  • Names sodium sulphate (½ mark)
  • pH = 7 (½ mark)
  • Dry HCl does not ionise, so no ions (1 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 paper2023 board paper, set 31/4/1: 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.