ScienceCBSE Class 10 · Board exam 2025, set 31/3/1 · 5 marks · Long answer

CBSE Class 10 Science 2025: question 34(b)

Set in the CBSE Class 10 board exam of 2025, paper 31/3/1, section D, question 34(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q34(b) · 5 marks · Long answerMetals and Non-metals

(i) With the help of balanced chemical equations state the process of extracting (I) mercury from its ore called cinnabar, and (II) copper from its sulphide ore.

(ii) Silver and copper articles slowly lose their shiny surfaces when exposed to air. Name the compounds formed on (I) silver articles, and (II) copper articles in the form of coating.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/3/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Metals low in the reactivity series are obtained by heating their sulphide ores in air.

Hint 2

Silver reacts with sulphur in air; copper with moist CO₂.

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.

(i)(I) Cinnabar (HgS) is roasted in air to convert it into mercuric oxide: $2 H g S (s) + 3 O_{2} (g) Heat 2 H g O (s) + 2 S O_{2} (g)$
1 mark
On further heating, mercuric oxide is reduced to mercury: $2 H g O (s) Heat 2 H g (l) + O_{2} (g)$
1 mark
(II) Copper glance ( $C u_{2} S$ ) is partially roasted in air: $2 C u_{2} S + 3 O_{2} (g) Heat 2 C u_{2} O + 2 S O_{2} (g)$
1 mark
The copper(I) oxide formed reacts with the remaining sulphide (self-reduction): $2 C u_{2} O + C u_{2} S Heat 6 C u (s) + S O_{2} (g)$
1 mark
(ii)(I) Silver articles get a black coating of silver sulphide, $A g_{2} S$ .
½ mark
(II) Copper articles get a green coating of basic copper carbonate, $C u C O_{3} \cdot C u (O H)_{2}$ .
½ mark

Answer: (i) $2 H g S + 3 O_{2} \to 2 H g O + 2 S O_{2}$ , $2 H g O \to 2 H g + O_{2}$ ; $2 C u_{2} S + 3 O_{2} \to 2 C u_{2} O + 2 S O_{2}$ , $2 C u_{2} O + C u_{2} S \to 6 C u + S O_{2}$ ; (ii) Ag₂S; basic copper carbonate

Where the marks are

Each of the four balanced equations (1 mark each; ½ deducted if unbalanced)
Silver sulphide (½ mark)
Basic copper carbonate (½ mark)

Revise the chapter

Chapter: Metals and Non-metals (notes, formulas, where marks are lost and every past question)

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 paper2025 board paper, set 31/3/1: every question, by section.

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CBSE Class 10 Science 2025: question 34(b)

Hints

Step-by-step solution

Revise the chapter

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