Class 12 Chemistry

Chapter 5 Solutions — Coordination Compounds

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Solutions

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Step-by-step NCERT solutions for Coordination Compounds (Chapter 5, CBSE Class 12 Chemistry) — every question and answer worked out in full, not just the final result. You can also read the Coordination Compounds textbook chapter.

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All 31 questions in Coordination Compounds are solved in the PDF. Here's what's inside, exercise by exercise:

Exercises

Explain the bonding in coordination compounds in terms of Werner's postulates.
FeSO₄ solution mixed with (NH₄)₂SO₄ solution in 1:1 molar ratio gives the test of Fe²⁺ ion but CuSO₄ solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of Cu²⁺ ion. Explain why?
Explain with two examples each of the following: coordination entity, ligand, coordination number, coordination polyhedron, homoleptic and heteroleptic.
What is meant by unidentate, didentate and ambidentate ligands? Give two examples for each.
5.
Specify the oxidation numbers of the metals in the following coordination entities:
- (i) [Co(H₂O)(CN)(en)₂]²⁺
- (ii) [CoBr₂(en)₂]⁺
- (iii) [PtCl₄]²⁻
- (iv) K₃[Fe(CN)₆]
- (v) [Cr(NH₃)₃Cl₃]
6.
Using IUPAC norms write the formulas for the following:
- (i) Tetrahydroxidozincate(II)
- (ii) Potassium tetrachloridopalladate(II)
- (iii) Diamminedichloridoplatinum(II)
- (iv) Potassium tetracyanidonickelate(II)
- (v) Pentaamminenitrito-O-cobalt(III)
- (vi) Hexaamminecobalt(III) sulphate
- (vii) Potassium tri(oxalato)chromate(III)
- (viii) Hexaammineplatinum(IV)
- (ix) Tetrabromidocuprate(II) (x)…
7.
Using IUPAC norms write the systematic names of the following:
- (i) [Co(NH₃)₆]Cl₃
- (ii) [Pt(NH₃)₂Cl(NH₂CH₃)]Cl
- (iii) [Ti(H₂O)₆]³⁺
- (iv) [Co(NH₃)₄Cl(NO₂)]Cl
- (v) [Mn(H₂O)₆]²⁺
- (vi) [NiCl₄]²⁻
- (vii) [Ni(NH₃)₆]Cl₂
- (viii) [Co(en)₃]³⁺
- (ix) [Ni(CO)₄]
List various types of isomerism possible for coordination compounds, giving an example of each.
9.
How many geometrical isomers are possible in the following coordination entities?
- (i) [Cr(C₂O₄)₃]³⁻
- (ii) [Co(NH₃)₃Cl₃]
10.
Draw the structures of optical isomers of:
- (i) [Cr(C₂O₄)₃]³⁻
- (ii) [PtCl₂(en)₂]²⁺
- (iii) [Cr(NH₃)₂Cl₂(en)]⁺
11.
Draw all the isomers (geometrical and optical) of:
- (i) [CoCl₂(en)₂]⁺
- (ii) [Co(NH₃)Cl(en)₂]²⁺
- (iii) [Co(NH₃)₂Cl₂(en)]⁺
Write all the geometrical isomers of [Pt(NH₃)(Br)(Cl)(py)] and how many of these will exhibit optical isomers?
13.
Aqueous copper sulphate solution (blue in colour) gives:
- (i) a green precipitate with aqueous potassium fluoride and
- (ii) a bright green solution with aqueous potassium chloride. Explain these experimental results.
What is the coordination entity formed when excess of aqueous KCN is added to an aqueous solution of copper sulphate? Why is it that no precipitate of copper sulphide is obtained when H₂S(g) is passed through this solution?
15.
Discuss the nature of bonding in the following coordination entities on the basis of valence bond theory:
- (i) [Fe(CN)₆]⁴⁻
- (ii) [FeF₆]³⁻
- (iii) [Co(C₂O₄)₃]³⁻
- (iv) [CoF₆]³⁻
Draw figure to show the splitting of d orbitals in an octahedral crystal field.
What is spectrochemical series? Explain the difference between a weak field ligand and a strong field ligand.
What is crystal field splitting energy? How does the magnitude of Do decide the actual configuration of d orbitals in a coordination entity?
[Cr(NH₃)₆]³⁺ is paramagnetic while [Ni(CN)₄]²⁻ is diamagnetic. Explain why?
A solution of [Ni(H₂O)₆]²⁺ is green but a solution of [Ni(CN)₄]²⁻ is colourless. Explain.
[Fe(CN)₆]⁴⁻ and [Fe(H₂O)₆]²⁺ are of different colours in dilute solutions. Why?
Discuss the nature of bonding in metal carbonyls.
23.
Give the oxidation state, d orbital occupation and coordination number of the central metal ion in the following complexes:
- (i) K₃[Co(C₂O₄)₃]
- (ii) cis-[CrCl₂(en)₂]Cl
- (iii) (NH₄)₂[CoF₄]
- (iv) [Mn(H₂O)₆]SO₄
24.
Write down the IUPAC name for each of the following complexes and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex:
- (i) K[Cr(H₂O)₂(C₂O₄)₂].3H₂O
- (ii) [Co(NH₃)₅Cl]Cl₂
- (iii) [CrCl₃(py)₃]
- (iv) Cs[FeCl₄]
- (v) K₄[Mn(CN)₆]
Explain the violet colour of the complex [Ti(H₂O)₆]³⁺ on the basis of crystal field theory.
What is meant by the chelate effect? Give an example.
27.
Discuss briefly giving an example in each case the role of coordination compounds in:
- (i) biological systems
- (ii) medicinal chemistry
- (iii) analytical chemistry
- (iv) extraction/metallurgy of metals.
28.
How many ions are produced from the complex Co(NH₃)₆Cl₂ in solution?
- (i) 6
- (ii) 4
- (iii) 3
- (iv) 2
29.
Amongst the following ions which one has the highest magnetic moment value?
- (i) [Cr(H₂O)₆]³⁺
- (ii) [Fe(H₂O)₆]²⁺
- (iii) [Zn(H₂O)₆]²⁺
30.
Amongst the following, the most stable complex is:
- (i) [Fe(H₂O)₆]³⁺
- (ii) [Fe(NH₃)₆]³⁺
- (iii) [Fe(C₂O₄)₃]³⁻
- (iv) [FeCl₆]³⁻
What will be the correct order for the wavelengths of absorption in the visible region for the following: [Ni(NO₂)₆]⁴⁻, [Ni(NH₃)₆]²⁺, [Ni(H₂O)₆]²⁺?

Sample

Worked examples

3 questions from Coordination Compounds, solved step by step.

Exercises

Explain the bonding in coordination compounds in terms of Werner's postulates.

Werner (1898) proposed the following postulates to explain bonding in coordination compounds:

1. Metals show two types of valences — primary (ionisable) and secondary (non-ionisable).

2. Primary valence is satisfied by negative ions and corresponds to the oxidation state of the metal. These are ionisable.

3. Secondary valence is the coordination number of the metal. It is fixed and non-ionisable. It is satisfied by neutral molecules or negative ions that bond directly to the metal (Lewis base donors).

4. The groups satisfying secondary valences are arranged in definite geometric patterns around the central metal ion (coordination polyhedra such as octahedral, tetrahedral, square planar).

Example: In [Co(NH₃)₆]Cl₃, Co³⁺ has primary valence = 3 (satisfied by 3 Cl⁻) and secondary valence = 6 (satisfied by 6 NH₃ molecules arranged octahedrally).

Werner distinguished species inside the coordination sphere (square bracket) from counter ions outside: only the counter ions ionise in solution, while the coordination sphere remains intact.

Answer: Werner postulated two valences: primary (ionisable, = oxidation state, satisfied by anions) and secondary (non-ionisable, = coordination number, satisfied by ligands arranged in a fixed geometry around the metal).

Exercises

FeSO₄ solution mixed with (NH₄)₂SO₄ solution in 1:1 molar ratio gives the test of Fe²⁺ ion but CuSO₄ solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of Cu²⁺ ion. Explain why?

FeSO₄ + (NH₄)₂SO₄ → FeSO₄.(NH₄)₂SO₄.6H₂O (Mohr's salt)

This is a double salt. In aqueous solution it dissociates completely into its constituent ions:

FeSO₄.(NH₄)₂SO₄ → Fe²⁺ + 2 NH₄⁺ + 2 SO₄²⁻

Free Fe²⁺ ions are present, so the characteristic tests for Fe²⁺ (e.g., with NaOH giving green precipitate, or with K₃[Fe(CN)₆] giving blue colour) are positive.

CuSO₄ + 4 NH₃ → [Cu(NH₃)₄]SO₄ (tetraamminecopper(II) sulphate)

This is a complex salt (coordination compound). In aqueous solution, [Cu(NH₃)₄]²⁺ complex ion does NOT dissociate significantly into Cu²⁺ and NH₃:

[Cu(NH₃)₄]²⁺ <→ Cu²⁺ + 4 NH₃ (Kd very small)

The concentration of free Cu²⁺ ions is negligibly small, so characteristic tests for Cu²⁺ (e.g., with NaOH giving blue precipitate) are not observed.

Difference: A double salt releases all its ions completely on dissolving; a complex (coordination compound) maintains the coordination entity intact in solution.

Answer: Mohr's salt is a double salt that releases free Fe²⁺ ions in solution; [Cu(NH₃)₄]SO₄ is a true coordination compound whose complex ion [Cu(NH₃)₄]²⁺ does not dissociate appreciably, so no free Cu²⁺ ions are available for the characteristic tests.

Exercises

What is meant by unidentate, didentate and ambidentate ligands? Give two examples for each.

1. Unidentate ligand:

A ligand that binds to the metal through only ONE donor atom.

Examples: Cl⁻ (donates through Cl); NH₃ (donates through N).

2. Didentate ligand:

A ligand that binds to the metal through TWO donor atoms simultaneously, forming a chelate ring.

Examples: en (H₂NCH₂CH₂NH₂, donates through 2 N atoms); C₂O₄²⁻ (oxalate, donates through 2 O atoms).

3. Ambidentate ligand:

A ligand that has TWO different potential donor atoms but uses only ONE of them at a time in a given complex.

Examples: NO₂⁻ can bind through N (giving nitro, -NO₂) or through O (giving nitrito, -ONO); SCN⁻ can bind through S (giving thiocyanato, M-SCN) or through N (giving isothiocyanato, M-NCS).

Answer: Unidentate (1 donor atom): Cl⁻, NH₃. Didentate (2 donor atoms): en, C₂O₄²⁻. Ambidentate (2 possible donor atoms, only 1 used at a time): NO₂⁻ (N or O), SCN⁻ (S or N).

All 31 questions in Coordination Compounds are solved step by step in the Solutions PDF above.

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Chapter 5 Solutions — Coordination Compounds

Overview

What these solutions cover

Exercises

Worked examples

Explain the bonding in coordination compounds in terms of Werner's postulates.

FeSO₄ solution mixed with (NH₄)₂SO₄ solution in 1:1 molar ratio gives the test of Fe²⁺ ion but CuSO₄ solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of Cu²⁺ ion. Explain why?

What is meant by unidentate, didentate and ambidentate ligands? Give two examples for each.

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