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The oxidation number of… (Class 12 Chemistry 2024, Q29a)

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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(a)

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

Q29(a) · 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)

    Define Chelate effect. How it affects the stability of complex ?

    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

For (a), think of , which can bind through N or O.

Hint 2

For (b), see which ion is coordinated and which is a counter ion; for (c), think of rings formed by ligands like en.

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 can bind to the metal through either one of them. Example: binds through N (nitrito-N) or through O (nitrito-O); binds through S or N.

    1 mark

  2. (b) The two compounds exchange the ion inside and outside the coordination sphere (/), so they give different ions in solution. This is ionisation isomerism.

    1 mark

  3. (c) Chelate effect: a bidentate or polydentate ligand binds a metal ion through two or more donor atoms, forming a ring (chelate).

    1 mark

  4. (c) Chelate complexes are more stable than comparable complexes of monodentate ligands; the greater the chelation, the greater the stability.

    1 mark

Answer: (a) Ligand with two different donor atoms, e.g. ; (b) Ionisation isomerism; (c) Ring formation by polydentate ligand; chelation increases stability

Where the marks are

  • Definition of ambidentate ligand (½ mark) with example (½ mark)
  • Ionisation isomerism (1 mark)
  • Definition of chelate effect (1 mark)
  • Chelation increases stability (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.