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

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

CBSE Class 10 Science 2023: question 28

Set in the CBSE Class 10 board exam of 2023, 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

Answer the following.

  1. (a)

    Suggest one remedial measure each to counteract the change in pH in human beings in following cases :
    (i) Production of too much acid in stomach during indigestion
    (ii) Stung by a honey bee / nettle leaves

    0 marks
  2. (b)

    Fresh milk has a pH of 6. When it changes into curd will its pH increase or decrease ? Why ?

    0 marks

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

Hints

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

Hint 1

Both situations involve too much acid. What type of substance neutralises an acid?

Hint 2

When milk becomes curd, a new acid forms. Does more acidity mean a higher or lower pH?

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. (a)(i) Excess acid in the stomach lowers the pH. Taking an antacid, a mild base such as milk of magnesia (magnesium hydroxide), neutralises the excess acid.

    1 mark

  2. (a)(ii) A bee sting or nettle sting injects methanoic acid into the skin. Rubbing on a mild base such as baking soda solution neutralises it and gives relief. For a nettle sting, the leaf of the dock plant can also be rubbed on.

    1 mark

  3. (b) The pH will decrease.

    ½ mark

  4. Reason: when milk sets into curd, bacteria convert lactose into lactic acid. Curd is therefore more acidic than milk, so its pH falls below 6.

    ½ mark

Answer: (a)(i) Take an antacid (e.g., milk of magnesia); (ii) apply baking soda solution or a mild base (dock leaf for nettle); (b) pH decreases because curd contains lactic acid and is more acidic.

Where the marks are

  • Use of antacid or mild base (1 mark)
  • Baking soda, a mild base or dock plant for the sting (1 mark)
  • pH decreases (½ mark)
  • Curd is more acidic due to lactic acid (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 paper2023 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.