Q37
4 marksSection E

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. (a) What happens when copper is heated in air? (Give the equation of the reaction involved). (b) Why are some metal oxides categorized as amphoteric? Give one example. (c) Complete the following equations: (i) Na2O(s)+H2O(l)→\mathrm{Na_2O_{(s)} + H_2O_{(l)} \rightarrow} (ii) Al2O3+2NaOH→\mathrm{Al_2O_3 + 2NaOH \rightarrow} 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?

Metals and Non-metals
Chemical Properties of Metals
Official Answer

Detailed answers to parts (a), (b), and (c) / OR (c) are provided below.

copper(II) oxideblack oxide2Cu+O2→2CuO2\mathrm{Cu} + \mathrm{O}_2 \rightarrow 2\mathrm{CuO}amphoteric oxidesAluminium oxideNaAlO2\mathrm{NaAlO}_2Sulphur dioxideacidicno action on dry litmus

Marking Scheme

  • 1Part (a): 1 Mark (0.5 mark for description, 0.5 mark for balanced chemical equation)
  • 2Part (b): 1 Mark (0.5 mark for definition of amphoteric oxide, 0.5 mark for example)
  • 3Part (c): 2 Marks (1 mark for each correctly completed and balanced equation) OR OR-Part (c): 2 Marks (0.5 mark for each sub-part i, ii, iii, iv)

Hint

Remember that copper forms a black oxide, amphoteric oxides react with both acids and bases, and dry gases do not change the colour of dry litmus paper.

Quick Oral Answer

Amphoteric oxides are metal oxides that react with both acids and bases to form salt and water. An example is aluminium oxide, which reacts with sodium hydroxide to form sodium aluminate and water.

Analysis & Explanation

This case-based question tests the understanding of the chemical properties of metals and non-metals when they react with oxygen.

  • Copper reacts with oxygen at high temperatures to form black copper(II) oxide (2Cu+O2→2CuO2\mathrm{Cu} + \mathrm{O}_2 \rightarrow 2\mathrm{CuO}).
  • Most metal oxides are basic, but oxides of aluminium and zinc are amphoteric because they react with both acids (like HCl\mathrm{HCl}) and bases (like NaOH\mathrm{NaOH}) to yield salt and water.
  • Sodium oxide dissolves in water to form a strong alkali, sodium hydroxide (NaOH\mathrm{NaOH}).
  • Non-metals like sulphur burn in oxygen to form acidic oxides like sulphur dioxide (SO2\mathrm{SO}_2). Acidic gases require moisture to show their acidic properties on litmus paper; hence, dry litmus paper shows no change.

Common Mistakes

  1. 1Writing the formula of copper(II) oxide as Cu2O\mathrm{Cu_2O} instead of CuO\mathrm{CuO}.
  2. 2Forgetting to balance the chemical equations, especially the reaction of aluminium oxide with sodium hydroxide.
  3. 3Stating that dry sulphur dioxide gas will turn dry blue litmus paper red, forgetting that moisture is mandatory for acidic behavior.

Interesting Facts

Anodising is an electrochemical process that thickens the natural protective oxide layer on aluminium, making it highly corrosion-resistant and allowing it to be dyed in vibrant colours.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2023?

This question carries 4 marks in the CBSE Class 10 Science 2023 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Metals and Non-metals" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Chemical Properties of Metals" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2023 paper?

This question appears in Section E in the CBSE Class 10 Science 2023 paper.