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Almost all metals combine… (Class 10 Science 2023, Q37)

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ScienceCBSE Class 10 · Board exam 2023, set 31/1/1 · 4 marks · Case-based

CBSE Class 10 Science 2023: question 37

Set in the CBSE Class 10 board exam of 2023, paper 31/1/1, section E, question 37, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q37 · 4 marks · Case-basedCompetency-basedMetals and Non-metals

Almost all metals combine with oxygen to form metal oxides. Metal oxides are generally basic in nature. But some metal oxides show both basic as well as acidic behaviour. Different metals show different reactivities towards oxygen. Some react vigorously while some do not react at all.

  1. (a)

    What happens when copper is heated in air ? (Give the equation of the reaction involved).

    1 mark
  2. (b)

    Why are some metal oxides categorized as amphoteric ? Give one example.

    1 mark
  3. (c)

    Complete the following equations :
    (i)
    (ii)

    2 marks

  4. OR

    (c)

    On burning Sulphur in oxygen a colourless gas is produced.
    (i) Write chemical equation for the reaction.
    (ii) Name the gas formed.
    (iii) State the nature of the gas.
    (iv) What will be the action of this on a dry litmus paper ?

    2 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

Copper turns black when heated in air. Which compound is that?

Hint 2

'Amphoteric' means the oxide behaves like an acid and like a base.

Hint 3

Metal oxide + water gives a hydroxide. SO₂ shows acidic behaviour only when water is present.

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) When copper is heated in air, it combines with oxygen and forms black copper(II) oxide. The surface turns black:

    1 mark

  2. (b) Some metal oxides are called amphoteric because they react with both acids and bases to give salt and water.

    ½ mark

  3. Example: aluminium oxide, (or zinc oxide, ZnO).

    ½ mark

  4. (c)(a)(i) Sodium oxide dissolves in water and forms sodium hydroxide, an alkali:

    1 mark

  5. (c)(a)(ii) Here aluminium oxide behaves as an acidic oxide and forms sodium aluminate and water:

    1 mark

  6. (c)(b) [alternative choice, 2 marks if attempted instead of (c)(a)] (i) (½ mark)

  7. (c)(b)(ii) The gas is sulphur dioxide (½ mark). (iii) It is acidic in nature, being an oxide of a non-metal (½ mark).

  8. (c)(b)(iv) On dry litmus paper there is no change, because the gas forms an acid (sulphurous acid) only when water is present (½ mark).

Answer: (a) 2Cu + O₂ → 2CuO (black copper oxide); (b) they react with both acids and bases to form salt and water, e.g. Al₂O₃/ZnO; (c)(a) (i) 2NaOH(aq), (ii) 2NaAlO₂ + H₂O; (c)(b) (i) S + O₂ → SO₂, (ii) sulphur dioxide, (iii) acidic, (iv) no change on dry litmus

Where the marks are

  • Balanced equation 2Cu + O₂ → 2CuO (1 mark)
  • Reason: reacts with both acids and bases to give salt and water (½ mark)
  • Example Al₂O₃ or ZnO (½ mark)
  • Na₂O + H₂O → 2NaOH (1 mark)
  • Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (1 mark)
  • OR (c): S + O₂ → SO₂ (½), sulphur dioxide (½), acidic (½), no change on dry litmus (½) (2 marks)

Revise the chapter

Practise this chapterBoard-style questions from Metals and Non-metals, 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.