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Page No 258: - Chapter 9 Coordination Compunds Exercise Solutions class 12 ncert solutions Chemistry - SaraNextGen [2024-2025]

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On April 24, 2024, 11:35 AM

Question 9.1:

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

Answer:

Werner’s postulates explain the bonding in coordination compounds as follows:

(i) A metal exhibits two types of valencies namely, primary and secondary valencies. Primary valencies are satisfied by negative ions while secondary valencies are satisfied by both negative and neutral ions.

(In modern terminology, the primary valency corresponds to the oxidation number of the metal ion, whereas the secondary valency refers to the coordination number of the metal ion.

(ii) A metal ion has a definite number of secondary valencies around the central atom. Also, these valencies project in a specific direction in the space assigned to the definite geometry of the coordination compound.

(iii) Primary valencies are usually ionizable, while secondary valencies are non-ionizable.

Question 9.2:

FeSO₄ solution mixed with (NH₄)₂SO₄ solution in 1:1 molar ratio gives the test of Fe²⁺ion but CuSO₄solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of Cu²⁺ ion. Explain why?

Answer:

Both the compounds i.e., and fall under the category of addition compounds with only one major difference i.e., the former is an example of a double salt, while the latter is a coordination compound.

A double salt is an addition compound that is stable in the solid state but that which breaks up into its constituent ions in the dissolved state. These compounds exhibit individual properties of their constituents. For e.g. breaks into Fe²⁺, NH⁴⁺, and SO₄²⁻ ions. Hence, it gives a positive test for Fe²⁺ ions.

A coordination compound is an addition compound which retains its identity in the solid as well as in the dissolved state. However, the individual properties of the constituents are lost. This happens because does not show the test for Cu²⁺. The ions present in the solution of are and .

Question 9.3:

Explain with two examples each of the following: coordination entity, ligand, coordination number, coordination polyhedron, homoleptic and heteroleptic.

Answer:

(i) Coordination entity:

A coordination entity is an electrically charged radical or species carrying a positive or negative charge. In a coordination entity, the central atom or ion is surrounded by a suitable number of neutral molecules or negative ions ( called ligands). For example:

= cationic complex

= anionic complex

= neutral complex

(ii) Ligands

The neutral molecules or negatively charged ions that surround the metal atom in a coordination entity or a coordinal complex are known as ligands. For example, , Cl⁻, ⁻OH. Ligands are usually polar in nature and possess at least one unshared pair of valence electrons.

(iii) Coordination number:

The total number of ligands (either neutral molecules or negative ions) that get attached to the central metal atom in the coordination sphere is called the coordination number of the central metal atom. It is also referred to as its ligancy.

For example:

(a) In the complex, K₂[PtCl₆], there as six chloride ions attached to Pt in the coordinate sphere. Therefore, the coordination number of Pt is 6.

(b) Similarly, in the complex [Ni(NH₃)₄]Cl₂, the coordination number of the central atom (Ni) is 4.

(vi) Coordination polyhedron:

Coordination polyhedrons about the central atom can be defined as the spatial arrangement of the ligands that are directly attached to the central metal ion in the coordination sphere. For example:

(a)

(b) Tetrahedral

(v) Homoleptic complexes:

These are those complexes in which the metal ion is bound to only one kind of a donor group. For eg: etc.

(vi) Heteroleptic complexes:

Heteroleptic complexes are those complexes where the central metal ion is bound to more than one type of a donor group.

For e.g.:

Question 9.4:

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

Answer:

A ligand may contain one or more unshared pairs of electrons which are called the donor sites of ligands. Now, depending on the number of these donor sites, ligands can be classified as follows:

(a) Unidentate ligands: Ligands with only one donor sites are called unidentate ligands. For e.g., , Cl⁻ etc.

(b) Didentate ligands: Ligands that have two donor sites are called didentate ligands. For e.g.,

(a) Ethane-1,2-diamine

(b) Oxalate ion

(c) Ambidentate ligands:

Ligands that can attach themselves to the central metal atom through two different atoms are called ambidentate ligands. For example:

(a)

(The donor atom is N)

(The donor atom is oxygen)

(b)

(The donor atom is S)

(The donor atom is N)

Question 9.5:

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]

Answer:

(i)

Let the oxidation number of Co be x.

The charge on the complex is +2.

(ii)

Let the oxidation number of Pt be x.

The charge on the complex is −2.

x + 4(−1) = −2

x = + 2

(iv)

Question 9.6:

Using IUPAC norms write the formulas for the following:

(i) Tetrahydroxozincate(II)

(ii) Potassium tetrachloridopalladate(II)

(iii) Diamminedichloridoplatinum(II)

(iv) Potassium tetracyanonickelate(II)

(v) Pentaamminenitrito-O-cobalt(III)

(vi) Hexaamminecobalt(III) sulphate

(vii) Potassium tri(oxalato)chromate(III)

(viii) Hexaammineplatinum(IV)

(ix) Tetrabromidocuprate(II)

(x) Pentaamminenitrito-N-cobalt(III)

Answer:

(i) [Zn(OH)₄]²⁻

(ii) K₂[PdCl₄]

(iii) [Pt(NH₃)₂Cl₂]

(iv) K₂[Ni(CN)₄]

(v) [Co(ONO) (NH₃)₅]²⁺

(vi) [Co(NH₃)₆]₂ (SO₄)₃

(vii) K₃[Cr(C₂O₄)₃]

(viii) [Pt(NH₃)₆]⁴⁺

(ix) [Cu(Br)₄]²⁻

(x) [Co[NO₂)(NH₃)₅]²⁺

Question 9.7:

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]

Answer:

(i) Hexaamminecobalt(III) chloride

(ii) Diamminechlorido(methylamine) platinum(II) chloride

(iii) Hexaquatitanium(III) ion

(iv) Tetraamminichloridonitrito-N-Cobalt(III) chloride

(v) Hexaquamanganese(II) ion

(vi) Tetrachloridonickelate(II) ion

(vii) Hexaamminenickel(II) chloride

(viii) Tris(ethane-1, 2-diammine) cobalt(III) ion

(ix) Tetracarbonylnickel(0)

Question 9.8:

List various types of isomerism possible for coordination compounds, giving an example of each.

Answer:

(a) Geometric isomerism:

This type of isomerism is common in heteroleptic complexes. It arises due to the different possible geometric arrangements of the ligands. For example:

(b) Optical isomerism:

This type of isomerism arises in chiral molecules. Isomers are mirror images of each other and are non-superimposable.

(c) Linkage isomerism: This type of isomerism is found in complexes that contain ambidentate ligands. For example:

[Co(NH₃)₅ (NO₂)]Cl₂ and [Co(NH₃)₅ (ONO)Cl₂

Yellow form Red form

(d) Coordination isomerism:

This type of isomerism arises when the ligands are interchanged between cationic and anionic entities of differnet metal ions present in the complex.

[Co(NH₃)₆] [Cr(CN)₆] and [Cr(NH₃)₆] [Co(CN)₆]

(e) Ionization isomerism:

This type of isomerism arises when a counter ion replaces a ligand within the coordination sphere. Thus, complexes that have the same composition, but furnish different ions when dissolved in water are called ionization isomers. For e.g., Co(NH₃)₅SO₄)Br and Co(NH₃)₅Br]SO_4.

(f) Solvate isomerism:

Solvate isomers differ by whether or not the solvent molecule is directly bonded to the metal ion or merely present as a free solvent molecule in the crystal lattice.

[Cr[H₂O)₆]Cl₃ [Cr(H₂O)₅Cl]Cl₂⋅H₂O [Cr(H₂O)₅Cl₂]Cl⋅2H₂O