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In the experimental setup… (Class 10 Science 2023, Q1)

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ScienceCBSE Class 10 · Board exam 2023, set 31/1/1 · 1 mark · MCQ

CBSE Class 10 Science 2023: question 1

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

Q1 · 1 mark · MCQCompetency-basedAcids, Bases and Salts

In the experimental setup given below, it is observed that on passing the gas produced in the reaction in the solution 'X' the solution 'X' first turns milky and then colourless.

The option that justifies the above stated observation is that 'X' is aqueous calcium hydroxide and

  1. (A)it turns milky due to carbon dioxide gas liberated in the reaction and after sometime it becomes colourless due to formation of calcium carbonate.
  2. (B)it turns milky due to formation of calcium carbonate and on passing excess of carbon dioxide it becomes colourless due to formation of calcium hydrogen carbonate which is soluble in water.
  3. (C)it turns milky due to passing of carbon dioxide through it. It turns colourless as on further passing carbon dioxide, sodium hydrogen carbonate is formed which is soluble in water.
  4. (D)the carbon dioxide liberated during the reaction turns lime water milky due to formation of calcium hydrogen carbonate and after some time it turns colourless due to formation of calcium carbonate which is soluble in water.

Figure in the paper: Apparatus: a boiling tube clamped on a stand containing sodium carbonate and dilute hydrochloric acid, closed with a cork fitted with a delivery tube that leads into a test tube (held by hand) containing solution 'X'. Labels: Dilute Hydrochloric Acid, Sodium carbonate, X. See it in the official paper.

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

Which gas is given off when a carbonate reacts with an acid?

Hint 2

Milkiness comes from an insoluble product. Think about what happens when more of the gas is passed through it.

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.

  1. Sodium carbonate reacts with dilute HCl and releases carbon dioxide:

  2. turns lime water milky because insoluble calcium carbonate forms:

  3. With excess , soluble calcium hydrogen carbonate forms and the milkiness disappears: . This matches option (B).

    1 mark

Answer: Option (B)

Where the marks are

  • Chooses (B): milky from , colourless from soluble (1 mark)

Revise the chapter

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

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.