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Write one chemical equation… (Class 10 Science 2024, Q27)

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ScienceCBSE Class 10 · Board exam 2024, set 31/1/1 · 3 marks · Short answer

CBSE Class 10 Science 2024: question 27

Set in the CBSE Class 10 board exam of 2024, 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

Write one chemical equation each for the chemical reaction in which the following have taken place :
(i) Change in colour
(ii) Change in temperature
(iii) Formation of precipitate
Mention colour change/temperature change (rise/fall)/compound precipitated along with equation.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/1/1.

Hints

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

Hint 1

Recall the NCERT activities: an iron nail in blue solution, an acid mixed with a base, and two colourless solutions giving a yellow solid.

Hint 2

For each one, write the balanced equation and state exactly what you observe (colour, rise or fall in temperature, name of the precipitate).

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. (i) Change in colour: an iron nail placed in copper sulphate solution turns the blue solution pale green.

    ½ mark

  2. ½ mark

  3. (ii) Change in temperature: neutralisation of sodium hydroxide with hydrochloric acid releases heat, so the temperature rises.

    ½ mark

  4. ½ mark

  5. (iii) Formation of precipitate: a **yellow precipitate of lead iodide ()** forms.

    ½ mark

  6. ½ mark

Answer: (i) Fe + CuSO₄, blue to green; (ii) NaOH + HCl, temperature rises; (iii) Pb(NO₃)₂ + 2KI, yellow PbI₂ precipitate

Where the marks are

  • Colour change stated (½ mark) with balanced equation (½ mark)
  • Temperature rise stated (½ mark) with balanced equation (½ mark)
  • Precipitate named (½ mark) with balanced equation (½ mark)

Revise the chapter

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 paper2024 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.