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(i) The pH of a sample of… (Class 10 Science 2024, Q28)

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ScienceCBSE Class 10 · Board exam 2024, set 31/1/1 · 3 marks · Short answer

CBSE Class 10 Science 2024: question 28

Set in the CBSE Class 10 board exam of 2024, paper 31/1/1, section C, question 28, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q28 · 3 marks · Short answerCompetency-basedAcids, Bases and Salts

(i) The pH of a sample of tomato juice is 4.6. How is this juice likely to be in taste? Give reason to justify your answer.
(ii) How do we differentiate between a strong acid and a weak base in terms of ion-formation in aqueous solutions?
(iii) The acid rain can make the survival of aquatic animals difficult. How?

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/1/1.

Hints

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

Hint 1

Compare 4.6 with the neutral value of 7.

Hint 2

Strength depends on how many ions are produced in water. Living organisms can tolerate only a narrow pH range.

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) The tomato juice will taste sour (slightly).

    ½ mark

  2. Reason: a pH of 4.6 is less than 7, so the juice is acidic, and acids taste sour.

    ½ mark

  3. (ii) A strong acid ionises almost completely in water and gives a large concentration of () ions.

    ½ mark

  4. A weak base ionises only partially in water and gives a small concentration of ions.

    ½ mark

  5. (iii) Aquatic animals survive only in a narrow pH range of about 7.0 to 7.8. Acid rain (pH below 5.6) lowers the pH of river water outside this range, so their survival becomes difficult.

    1 mark

Answer: (i) Sour, since pH < 7 means acidic; (ii) strong acid gives many H⁺ ions, weak base gives few OH⁻ ions; (iii) acid rain lowers river pH below the 7.0–7.8 range animals need

Where the marks are

  • Sour taste (½ mark) with reason that pH < 7 means acidic (½ mark)
  • Strong acid gives more H⁺ ions (½ mark)
  • Weak base gives fewer OH⁻ ions (½ mark)
  • Acid rain lowers pH below the survivable range of 7.0–7.8 (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 paper2024 board paper, set 31/1/1: 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.