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With the help of an… (Class 10 Science 2023, Q30)

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ScienceCBSE Class 10 · Board exam 2023, set 31/6/1 · 3 marks · Short answer

CBSE Class 10 Science 2023: question 30

Set in the CBSE Class 10 board exam of 2023, paper 31/6/1, section C, question 30, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q30 · 3 marks · Short answerChemical Reactions and Equations

With the help of an appropriate example, justify that some of the chemical reactions are determined by
(a) Change in temperature,
(b) Evolution of a gas, and
(c) Change in colour.

Give chemical equation for the reaction involved in each case.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/6/1.

Hints

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

Hint 1

Recall the NCERT activities: quicklime with water, and zinc with dilute acid.

Hint 2

For colour change, think of a displacement reaction with blue copper sulphate solution.

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) Change in temperature: quicklime reacts vigorously with water and releases a lot of heat.

    1 mark

  2. (b) Evolution of a gas: zinc granules react with dilute sulphuric acid and bubbles of hydrogen are seen.

    1 mark

  3. (c) Change in colour: an iron nail kept in blue copper sulphate solution turns the solution light green, and a brown coat of copper forms on the nail. . Another example is blue turning white on heating.

    1 mark

Answer: (a) CaO + H₂O → Ca(OH)₂ + heat; (b) Zn + H₂SO₄ → ZnSO₄ + H₂; (c) Fe + CuSO₄ → FeSO₄ + Cu (blue to green)

Where the marks are

  • Suitable reaction with heat change and equation (1 mark)
  • Suitable reaction evolving gas and equation (1 mark)
  • Suitable reaction with colour change and equation (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Chemical Reactions and Equations, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 31/6/1: 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.