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The oxidation number of… (Class 12 Chemistry 2024, Q29b)

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ChemistryCBSE Class 12 · Board exam 2024, set 56/5/1 · 4 marks · Case-based

CBSE Class 12 Chemistry 2024: question 29(b)

Set in the CBSE Class 12 board exam of 2024, paper 56/5/1, section D, question 29(b), for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q29(b) · 4 marks · Case-basedCompetency-basedCoordination Compounds

The oxidation number of the central atom in a complex is defined as the charge it would carry if all the ligands are removed along with the electron pairs that are shared with the central atom. Similarly the charge on the complex is the sum of the charges of the constituent parts i.e. the sum of the charges on the central metal ion and its surrounding ligands. Based on this, the complex is called neutral if the sum of the charges of the constituents is equal to zero. However, for an anion or cationic complex, the sum of the charges of the constituents is equal to the charge on the coordination sphere.

Based on the above information, answer the following questions :

  1. (a)

    Define ambidentate ligand with an example.

    1 mark
  2. (b)

    What type of isomerism is shown by and ?

    1 mark
  3. (c)

    Find the coordination number and oxidation state of chromium in .

    2 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 56/5/1.

Hints

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

Hint 1

Oxalate is a bidentate ligand with charge −2.

Hint 2

Three ions mean the complex ion carries a −3 charge.

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. (a) An ambidentate ligand has two different donor atoms and coordinates through either one of them, e.g. (N or O donor) or (S or N donor).

    1 mark

  2. (b) The two compounds give different ions in solution ( vs ), so they show ionisation isomerism.

    1 mark

  3. (c) Coordination number: each oxalate is bidentate, so 3 × 2 = 6.

    1 mark

  4. (c) Oxidation state: the complex ion is , so , giving +3.

    1 mark

Answer: (a) e.g. ; (b) Ionisation isomerism; (c) CN = 6, oxidation state = +3

Where the marks are

  • Ambidentate definition with example (½ + ½ marks)
  • Ionisation isomerism (1 mark)
  • Coordination number 6 (1 mark)
  • Oxidation state +3 (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Coordination Compounds, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 56/5/1: 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.