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When copper powder is heated… (Class 10 Science 2023, Q21b)

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ScienceCBSE Class 10 · Board exam 2023, set 31/2/1 · 2 marks · Very short answer

CBSE Class 10 Science 2023: question 21(b)

Set in the CBSE Class 10 board exam of 2023, paper 31/2/1, section B, question 21(b), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q21(b) · 2 marks · Very short answerChemical Reactions and Equations

When copper powder is heated in a watch glass, a black substance is formed.

  1. (i)

    Why is this black substance formed ? Name it.

    1 mark
  2. (ii)

    How can this black substance be reversed to its original form ?

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/2/1.

Hints

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

Hint 1

Heating is done in open air. Which gas in air can combine with copper?

Hint 2

To get copper back, oxygen must be removed. Which gas is a common reducing agent?

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) When copper is heated in air, it combines with oxygen, so copper is oxidised:

    ½ mark

  2. (i) The black substance is copper(II) oxide, .

    ½ mark

  3. (ii) Pass hydrogen gas over the heated black copper oxide. It is reduced back to brown copper:

    1 mark

Answer: (i) Copper is oxidised by oxygen of air; black substance is copper oxide (CuO). (ii) By passing hydrogen gas over heated CuO: CuO + H₂ → Cu + H₂O

Where the marks are

  • Reason: copper combines with oxygen, i.e. it is oxidised (½ mark)
  • Names the substance as copper oxide, CuO (½ mark)
  • Reverses it by passing hydrogen over heated CuO, with or without the 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 31/2/1: 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.