Chapter 9: Coordination Compounds

Q25Written answer

A coordination compound CrCl3.4H2O precipitates silver chloride when treated with silver nitrate. The molar conductance of its solution corresponds to a total of two ions. Write the structural formula of the compound and name it.

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Worked solution

If it forms silver chloride then there is one free chlorine atom outside the coordination sphere. The structural formula has to be [Cr(H2O)4Cl2]Cl. The name of this complex is tetraaquadichlorido chromium(III) chloride.

Q26Written answer

A complex of the type [M(AA)2X2]n+is known to be optically active. What does this indicate about the structure of the complex? Give one example of such complex.

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Worked solution

The structure has to be cis-octahedral.

Example for such a complex is [Co(en)2Cl2]+ which is optically active.

Q27Written answer

The magnetic moment of [MnCl4]2– is 5.92 BM. Explain giving a reason.

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Worked solution

A magnetic moment of 5.92 BM means there are 5 unpaired electrons because

Magnetic Moment = √ n(n+2)

The geometry tetrahedral with 5 unpaired electrons giving a magnetic moment of 5.92 BM as the four ligands are attached to Mn2+.

Q28Written answer

Based on crystal field theory explain why Co(III) forms a paramagnetic octahedral complex with weak field ligands whereas it forms a diamagnetic octahedral complex with strong field ligands.

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The electronic configuration will be t⁴_2g e²_g.It has 4 unpaired electron and paramagnetic. With weal ligand Δ₀ < p. The configuration with strong field ligand will be t⁶_2g e⁰_g. the Δ₀ > p and there won’t be any unpaired electron therefore diamagnetic.

Q29Written answer

Why are low spin tetrahedral complexes not formed?

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Worked solution

For tetrahedral complexes, the crystal field splitting energy is too low. It is lower than pairing energy so, the pairing of electrons is not favoured and therefore the complexes cannot form low spin complexes.

Q30Written answer

Give the electronic configuration of the following complexes based on

Crystal Field Splitting theory.

[CoF6]3–, [Fe(CN)6]4– and [Cu(NH3)6]2+.

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NCERT Exemplar Solutions of Class 12 Chemistry Chapter 9 Coordination Compounds-1

Q31Written answer

Explain why [Fe(H2O)6]3+ has a magnetic moment value of 5.92 BM whereas

[Fe(CN)6]3– has a value of only 1.74 BM.

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Worked solution

For [Fe(H2O)6]3+, H2O is a weak field ligand won’t cause pairing of electrons. So, the number of unpaired electrons will be 5.

Q32Written answer

Arrange following complex ions in increasing order of crystal field splitting energy (DO) :

[Cr(Cl)6]3–, [Cr(CN)6]3–, [Cr(NH3)6]3+.

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Worked solution

The increasing order of crystal field energy is

This is also the order of field strength of the ligands according to the spectrochemical series.

Q33Written answer

Why do compounds having similar geometry have a different magnetic moment?

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Worked solution

They differ in the number of paired and unpaired electrons. A strong field ligand will cause pairing of electrons while a weak field ligand will not cause pairing. Pairing or not pairing will change the number of unpaired electrons, which affects the magnetic moment.

Q34Written answer

CuSO4.5H2O is blue while CuSO4 is colourless. Why?

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Worked solution

In CuSO4.5H2O, there are water molecules that act as ligands. The electrons will excite to higher d orbital and show colour. Whereas, in CuSO4, there are no water molecules to act as ligands, so no crystal field splitting happens.

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II. Multiple Choice Questions (Type-II)