Answer the following. (a) Identify the reducing agent in the following reactions : (i) 4NH_3 + 5O_2 → 4NO + 6H_2O (ii) H_2O + F_2 → HF + HOF (iii) Fe_2O_3 + 3CO → 2Fe + 3CO_2 (iv) 2H_2 + O_2 → 2H_2O (b) Define a redox reaction in terms of gain or loss of oxygen.

ScienceCBSE Class 10 · Board exam 2023, set 31/1/1 · 3 marks · Short answer

CBSE Class 10 Science 2023: question 27

Set in the CBSE Class 10 board exam of 2023, paper 31/1/1, section C, question 27, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q27 · 3 marks · Short answerChemical Reactions and Equations

Answer the following.

(a)
Identify the reducing agent in the following reactions :
(i) $4 N H_{3} + 5 O_{2} \to 4 NO + 6 H_{2} O$
(ii) $H_{2} O + F_{2} \to HF + HOF$
(iii) $F e_{2} O_{3} + 3 CO \to 2 Fe + 3 C O_{2}$
(iv) $2 H_{2} + O_{2} \to 2 H_{2} O$
0 marks
(b)
Define a redox reaction in terms of gain or loss of oxygen.
0 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

A reducing agent is itself oxidised. Look for the substance that gains oxygen or loses hydrogen.

Hint 2

In (ii), check which reactant ends up with extra hydrogen. That one is reduced, so the other is the 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.

(a) A reducing agent is the substance that gets oxidised: it gains oxygen or loses hydrogen.
(a)(i) In $4 N H_{3} + 5 O_{2} \to 4 NO + 6 H_{2} O$ , $N H_{3}$ loses hydrogen and gains oxygen to form NO. **Reducing agent: $N H_{3}$ **.
½ mark
(a)(ii) In $H_{2} O + F_{2} \to HF + HOF$ , $F_{2}$ gains hydrogen (it is reduced), so $H_{2} O$ is the one giving up hydrogen. **Reducing agent: $H_{2} O$ **.
½ mark
(a)(iii) In $F e_{2} O_{3} + 3 CO \to 2 Fe + 3 C O_{2}$ , CO gains oxygen to become $C O_{2}$ . Reducing agent: CO.
½ mark
(a)(iv) In $2 H_{2} + O_{2} \to 2 H_{2} O$ , $H_{2}$ gains oxygen. **Reducing agent: $H_{2}$ **.
½ mark
(b) A redox reaction is one in which one substance gains oxygen (is oxidised) while another substance loses oxygen (is reduced), both at the same time.
1 mark

Answer: (a) (i) NH₃, (ii) H₂O, (iii) CO, (iv) H₂; (b) a reaction in which gain of oxygen by one substance and loss of oxygen by another occur simultaneously.

Where the marks are

NH₃ (½ mark)
H₂O (½ mark)
CO (½ mark)
H₂ (½ mark)
Defines redox as simultaneous gain and loss of oxygen (1 mark)

Revise the chapter

Chapter: Chemical Reactions and Equations (notes, formulas, where marks are lost and every past question)

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 31/1/1: every question, by section.

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CBSE Class 10 Science 2023: question 27

Hints

Step-by-step solution

Revise the chapter

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