2 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.

Q: 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.

The balanced chemical equation for the reaction is: $$\text{CuO(s)} + \text{H}_2\text{(g)} \xrightarrow{\text{Heat}} \text{Cu(s)} + \text{H}_2\text{O(g)}$$ (i) **Substance oxidized:** Hydrogen ($\text{H}_2$) is oxidized to water ($\text{H}_2\text{O}$) because it gains oxygen. (ii) **Substance reduced:** Copper (II) oxide ($\text{CuO}$) is reduced to copper ($\text{Cu}$) because it loses oxygen.

Redox Reactions

Official Answer

The balanced chemical equation for the reaction is:

$\text{CuO(s)} + \text{H}_2\text{(g)} \xrightarrow{\text{Heat}} \text{Cu(s)} + \text{H}_2\text{O(g)}$

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

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

CuOH2CuH2Ooxidizedreducedgains oxygenloses oxygen

Marking Scheme

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

Analysis & 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:

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

Common Mistakes

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

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.

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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.