A substance 'X' is used as a building material and is insoluble in water. When it reacts with dil. HCl, it produces a gas which turns lime water milky. (i) Write the chemical name and formula of 'X'. (ii) Write chemical equations for the chemical reactions involved in the above statements.

ScienceCBSE Class 10 · Board exam 2023, set 31/6/1 · 3 marks · Short answer

CBSE Class 10 Science 2023: question 28(a)

Set in the CBSE Class 10 board exam of 2023, paper 31/6/1, section C, question 28(a), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q28(a) · 3 marks · Short answerAcids, Bases and Salts

A substance 'X' is used as a building material and is insoluble in water. When it reacts with dil. HCl, it produces a gas which turns lime water milky.

(i)
Write the chemical name and formula of 'X'.
0 marks
(ii)
Write chemical equations for the chemical reactions involved in the above statements.
0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/6/1.

Hints

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

Hint 1

The gas that turns lime water milky is CO₂, so X must be a carbonate.

Hint 2

Which carbonate is used as a building material such as marble?

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) X is calcium carbonate,
½ mark
formula $CaC O_{3}$ (e.g. marble or limestone).
½ mark
(ii) With dilute HCl: $CaC O_{3} (s) + 2HCl (aq) \to CaC l_{2} (aq) + H_{2} O (l) + C O_{2} (g)$
1 mark
The $C O_{2}$ turns lime water milky: $Ca (OH)_{2} (aq) + C O_{2} (g) \to CaC O_{3} (s) + H_{2} O (l)$ . The milkiness is due to insoluble $CaC O_{3}$ .
1 mark

Answer: (i) Calcium carbonate, CaCO₃; (ii) CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ and Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Where the marks are

Chemical name calcium carbonate (½ mark)
Formula CaCO₃ (½ mark)
Balanced equation with HCl (1 mark)
Balanced equation for lime water turning milky (1 mark)

Revise the chapter

Chapter: Acids, Bases and Salts (notes, formulas, where marks are lost and every past question)

Practise this chapterBoard-style questions from Acids, Bases and Salts, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 31/6/1: every question, by section.

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CBSE Class 10 Science 2023: question 28(a)

Hints

Step-by-step solution

Revise the chapter

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