Chapter 5: Coordination Compounds Short Questions | chemistry Class 12 CBSE

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Chapter 5: Coordination Compounds Short Questions | chemistry Class 12 CBSE | ByteNotes.in

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Question 1

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State the main postulates of Werner's theory of coordination compounds.

Metals in coordination compounds show two types of valences: primary (ionisable, satisfied by negative ions) and secondary (non-ionisable, equal to the coordination number).
The secondary valence is non-ionisable and is satisfied by neutral molecules or negative ions directly bonded to the metal ion.
Ions or groups bound by secondary linkages have characteristic spatial arrangements (coordination polyhedra) corresponding to different coordination numbers.

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Question 2

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Differentiate between a double salt and a complex with one example of each.

Double salts (e.g., Mohr's salt, FeSO4.(NH4)2SO4.6H2O) dissociate completely into simple ions when dissolved in water and show the test for all constituent ions.
Complex compounds (e.g., K4[Fe(CN)6]) do not dissociate completely in water; the complex ion [Fe(CN)6]4- does not give the test for free Fe2+ or CN- ions.
Both are formed by combination of two or more stable compounds in stoichiometric ratios, but they differ fundamentally in their behaviour in aqueous solution.

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Question 3

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What is a chelate ligand? Why are chelate complexes more stable than complexes with unidentate ligands?

A chelate ligand is a di- or polydentate ligand that uses two or more donor atoms simultaneously to bind a single metal ion, forming ring-like (chelate ring) structures.
Chelate complexes are more stable than analogous complexes with unidentate ligands due to the chelate effect — the entropic advantage of forming ring structures increases overall thermodynamic stability.
The number of donor groups in a chelate ligand that bind simultaneously to a metal is called its denticity.

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Question 4

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Define an ambidentate ligand and give two examples, explaining the different modes of bonding.

An ambidentate ligand has two different donor atoms and can coordinate through either one in forming a complex; only one donor atom coordinates at a time.
NO2- (nitrite) can coordinate through nitrogen to give M-NO2 (nitro) linkage or through oxygen to give M-ONO (nitrito) linkage.
SCN- (thiocyanate) can coordinate through sulphur to give M-SCN (thiocyanato-S) or through nitrogen to give M-NCS (thiocyanato-N or isothiocyanato).

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Question 5

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What is the coordination number of Fe in [Fe(C2O4)3]3- and of Co in [Co(en)3]3+? Justify your answer.

The coordination number of Fe in [Fe(C2O4)3]3- is 6, because C2O42- (oxalate) is a didentate ligand that occupies two donor positions, and three such ligands give 3 x 2 = 6 donor atoms.
The coordination number of Co in [Co(en)3]3+ is also 6, because en (ethane-1,2-diamine) is a didentate ligand, and three en ligands provide 3 x 2 = 6 donor atoms.
Coordination number is determined only by the number of sigma bonds formed by ligand donor atoms with the central metal ion; pi bonds, if any, are not counted.

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Question 6

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Distinguish between homoleptic and heteroleptic complexes with one example each.

Homoleptic complexes are those in which a metal is bound to only one kind of donor group or ligand throughout; for example, [Co(NH3)6]3+ where cobalt is bound only to NH3 molecules.
Heteroleptic complexes are those in which a metal is bound to more than one kind of donor group; for example, [Co(NH3)4Cl2]+ where cobalt is bound to both NH3 and Cl- ligands.
The distinction is important for predicting isomerism: heteroleptic complexes can exhibit geometric isomerism, while homoleptic complexes generally cannot.

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Question 7

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Write the IUPAC name of [Co(NH3)5Cl]Cl2 and [Ag(NH3)2][Ag(CN)2].

[Co(NH3)5Cl]Cl2 is named pentaamminechloridocobalt(III) chloride; the cation contains five ammine and one chlorido ligand around Co(III), with two chloride counter ions.
[Ag(NH3)2][Ag(CN)2] is named diamminesilver(I) dicyanidoargentate(I); the cation contains Ag(I) with two ammine ligands, and the anion contains Ag(I) with two cyanido ligands.
In complex anions, the metal name ends in -ate; argentate is used for silver in the anionic complex, while the cationic silver complex uses the element name silver.

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Question 8

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What is geometric isomerism? State why tetrahedral complexes do not show geometric isomerism.

Geometric isomerism arises in heteroleptic complexes due to different possible spatial arrangements of ligands; in cis isomers, identical ligands are adjacent, while in trans isomers they are opposite each other.
Tetrahedral complexes do not show geometric isomerism because the relative positions of all four unidentate ligands attached to the central metal atom are equivalent with respect to each other.
Geometric isomerism is observed in square planar complexes of the type [MX2L2] and in octahedral complexes of the type [MX2L4]; facial and meridional isomers also occur in octahedral [Ma3b3] types.

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Question 9

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What are optical isomers? Define enantiomers and chirality in the context of coordination compounds.

Optical isomers are mirror images of a coordination entity that cannot be superimposed on one another; they differ in the direction they rotate the plane of plane-polarised light.
Enantiomers are the two non-superimposable mirror image forms of a chiral molecule or ion; they are designated dextro (d) if they rotate polarised light to the right and laevo (l) if to the left.
A molecule or ion that cannot be superimposed on its mirror image is called chiral; optical isomerism is common in octahedral complexes containing didentate ligands.

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Question 10

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Explain linkage isomerism with the example of [Co(NH3)5(NO2)]Cl2.

Linkage isomerism arises in coordination compounds containing ambidentate ligands, which can bond to the metal through either of two different donor atoms.
In [Co(NH3)5(NO2)]Cl2, the nitrite ligand (NO2-) can coordinate through nitrogen (-NO2) to give a yellow form or through oxygen (-ONO) to give a red form.
These two forms are called linkage isomers and were first discovered by Jorgensen; they have identical molecular formulas but differ in the donor atom of the ambidentate ligand.

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Question 11

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Define ionisation isomerism and give one example.

Ionisation isomerism arises when the counter ion in a complex salt is itself a potential ligand and can displace a ligand which then becomes the counter ion.
Example: [Co(NH3)5(SO4)]Br and [Co(NH3)5Br]SO4 are ionisation isomers; in the first, SO42- is coordinated and Br- is the counter ion, while in the second, Br- is coordinated and SO42- is the counter ion.
These isomers can be distinguished by their different reactions with reagents like AgNO3 or BaCl2 which precipitate specific free ions.

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Question 12

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What is solvate (hydrate) isomerism? Illustrate with the example of chromium complexes.

Solvate isomerism (hydrate isomerism when water is involved) arises when a solvent molecule (water) is either directly bonded to the metal ion within the coordination sphere or present as free solvent in the crystal lattice.
Example: [Cr(H2O)6]Cl3 (violet) and [Cr(H2O)5Cl]Cl2.H2O (grey-green) are solvate isomers with the same molecular formula but different properties.
In the violet form, all six water molecules are coordinated; in the grey-green form, one water is displaced from the coordination sphere to the lattice and replaced by one chloride as a ligand.

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Question 13

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Explain the hybridisation and geometry of [Co(NH3)6]3+ according to VBT.

In [Co(NH3)6]3+, cobalt is in +3 oxidation state with electronic configuration 3d6; the three 3d electrons pair up to leave two 3d orbitals vacant under the influence of NH3 (strong field ligand).
The two vacant 3d orbitals combine with one 4s and three 4p orbitals to give d2sp3 hybridisation, resulting in an octahedral geometry.
Since inner (n-1)d orbitals are used, [Co(NH3)6]3+ is called an inner orbital or low spin complex; it is diamagnetic due to the absence of unpaired electrons.

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Chapter 5: Coordination Compounds | Short Questions

State the main postulates of Werner's theory of coordination compounds.

Differentiate between a double salt and a complex with one example of each.

What is a chelate ligand? Why are chelate complexes more stable than complexes with unidentate ligands?

Define an ambidentate ligand and give two examples, explaining the different modes of bonding.

What is the coordination number of Fe in [Fe(C2O4)3]3- and of Co in [Co(en)3]3+? Justify your answer.

Distinguish between homoleptic and heteroleptic complexes with one example each.

Write the IUPAC name of [Co(NH3)5Cl]Cl2 and [Ag(NH3)2][Ag(CN)2].

What is geometric isomerism? State why tetrahedral complexes do not show geometric isomerism.

What are optical isomers? Define enantiomers and chirality in the context of coordination compounds.

Explain linkage isomerism with the example of [Co(NH3)5(NO2)]Cl2.

Define ionisation isomerism and give one example.

What is solvate (hydrate) isomerism? Illustrate with the example of chromium complexes.

Explain the hybridisation and geometry of [Co(NH3)6]3+ according to VBT.

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