Question 52 marksShort AnswerSection SECTION-A

When hydrogen gas is passed over heated copper (II) oxide, copper and steam are formed. Write the balanced chemical equation for this reaction and state (i) the substance oxidized and (ii) the substance reduced in the reaction.

Redox Reactions

Official answer

The balanced chemical equation for the reaction is:

CuO(s)+H2(g)→HeatCu(s)+H2O(g)\text{CuO(s)} + \text{H}_2\text{(g)} \xrightarrow{\text{Heat}} \text{Cu(s)} + \text{H}_2\text{O(g)}


(i) Substance oxidized: Hydrogen (H2\text{H}_2) is oxidized to water (H2O\text{H}_2\text{O}) because it gains oxygen.

(ii) Substance reduced: Copper (II) oxide (CuO\text{CuO}) is reduced to copper (Cu\text{Cu}) because it loses oxygen.

Answer keywords:CuOH2CuH2Ooxidizedreducedgains oxygenloses oxygen

Marking scheme

  1. 1.Writing the correct balanced chemical equation with state symbols: 1 Mark
  2. 2.Correctly identifying the substance oxidized (H2\text{H}_2): 0.5 Mark
  3. 3.Correctly identifying the substance reduced (CuO\text{CuO}): 0.5 Mark

Hint

Identify which reactant gains oxygen (oxidized) and which reactant loses oxygen (reduced) during the reaction.

Quick oral answer

When hydrogen is passed over heated copper oxide, copper oxide loses oxygen to form copper, so it is reduced. Hydrogen gains oxygen to form water, so it is oxidized. The balanced equation is CuO+H2→Cu+H2O\text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O}.

Common mistakes

  1. 1.Writing ionic species like Cu2+\text{Cu}^{2+} or H+\text{H}^+ instead of the complete molecular formulas (CuO\text{CuO} and H2\text{H}_2) as the substances oxidized or reduced.
  2. 2.Confusing the products (Cu\text{Cu} and H2O\text{H}_2\text{O}) as the substances oxidized or reduced; remember that reactants are always the substances that undergo oxidation or reduction.

Analysis and explanation

In a redox reaction, oxidation and reduction occur simultaneously. Oxidation is defined as the gain of oxygen or loss of hydrogen, while reduction is defined as the loss of oxygen or gain of hydrogen.

In this reaction:

  1. Hydrogen gas (H2\text{H}_2) gains oxygen to form steam (H2O\text{H}_2\text{O}), which means it undergoes oxidation. Therefore, the substance oxidized is H2\text{H}_2.
  2. Copper (II) oxide (CuO\text{CuO}) loses oxygen to form copper metal (Cu\text{Cu}), which means it undergoes reduction. Therefore, the substance reduced is CuO\text{CuO}.

Interesting facts

If hot copper metal is exposed to air, it reacts with oxygen to form a black layer of copper (II) oxide. Passing hydrogen gas over this heated black oxide reverses the reaction, restoring the shiny brown copper metal.

Question details

Q5 of 36 questions

Board
CBSE
Class
Class 10
Subject
Science
Year
2014
Section
Section SECTION-A
Marks
2
Type
Short Answer
Topic
Redox Reactions
Bloom's level
Applying
Syllabus topic
Chemical reactions: Chemical equation, Balanced chemical equation, implications of a balanced chemical equation, types of chemical reactions: combination, decomposition, displacement, double displacement, precipitation, endothermic exothermic reactions, oxidation and reduction.

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Frequently asked questions

How many marks does this question carry in CBSE Class 10 Science 2014?

This question carries 2 marks in the CBSE Class 10 Science 2014 examination.

What topic does this question cover in Science?

This question covers the topic "Redox Reactions" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2014 paper?

This is a Short Answer question from Section SECTION-A in the CBSE Class 10 Science 2014 paper.