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

(In modern terminology, the primary valencycorresponds to the oxidation number of the metal ion, whereas the secondaryvalency refers to the coordination number of the metal ion.

(ii) A metal ion has a definite number of secondaryvalencies around the central atom. Also, these valencies project in a specificdirection in the space assigned to the definite geometry of the coordinationcompound.

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

Question - 12 : -
FeSO₄ solutionmixed with (NH₄)₂SO₄ solutionin 1:1 molar ratio gives the test of Fe²⁺ion but

Answer - 12 : - CuSO_4 solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of Cu_2+ ion. Explain why?

Answer

Both the compounds i.e.,

and

fall under the category of additioncompounds with only one major difference i.e., the former is an example of adouble salt, while the latter is a coordination compound.

A double salt is anaddition compound that is stable in the solid state but that which breaks upinto its constituent ions in the dissolved state. These compounds exhibitindividual properties of their constituents. For e.g.

breaksinto Fe²⁺, NH⁴⁺, and SO₄²⁻ ions. Hence, it gives a positive testfor Fe²⁺ ions.

A coordinationcompound is an addition compound which retains its identity in the solid aswell as in the dissolved state. However, the individual properties of theconstituents are lost. This happens because

does not show the test for Cu²⁺. The ions present inthe solution of

are

and

Question - 13 : -
Explain with twoexamples each of the following: coordination entity, ligand, coordinationnumber, coordination polyhedron, homoleptic and heteroleptic.

Answer - 13 : -

(i) Coordinationentity:

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

= cationic complex

= anionic complex

= neutral complex

(ii) Ligands

The neutral moleculesor negatively charged ions that surround the metal atom in a coordinationentity 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 ofvalence electrons.

(iii) Coordinationnumber:

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

For example:

(a)In the complex, K₂[PtCl₆], there as sixchloride ions attached to Pt in the coordinate sphere. Therefore, thecoordination 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) Coordinationpolyhedron:

Coordinationpolyhedrons about the central atom can be defined as the spatial arrangement ofthe ligands that are directly attached to the central metal ion in thecoordination sphere. For example:

(a)

(b) Tetrahedral

(v) Homolepticcomplexes:

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

(vi) Heterolepticcomplexes:

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

For e.g.:

Question - 14 : -
What is meant byunidentate, didentate and ambidentate ligands? Give two examples for each.

Answer - 14 : -

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

(a) Unidentate ligands: Ligandswith only one donor sites are called unidentate ligands. For e.g.,

, Cl⁻ etc.

(b) Didentateligands: Ligands that have two donor sites are called didentateligands. For e.g.,

(a) Ethane-1,2-diamine

(b) Oxalate ion

Ligands that can attach themselves to thecentral 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 - 15 : - Specify the oxidation numbers of the metals in the following coordination entities:

Answer - 15 : -

(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)

Letthe oxidation number of Co be x.

The charge on the complex is +2.

(ii)

Letthe oxidation number of Pt be x.

The charge on the complex is −2.

x + 4(−1) = −2

x = + 2

(iv)

Question - 16 : -
Using IUPAC norms write the formulas for thefollowing:

Answer - 16 : -

(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 - 17 : -
Using IUPAC norms write the systematic namesof the following:

Answer - 17 : -

(i) [Co(NH_3)6]Cl_3

(ii) [Pt(NH_3)_2Cl(NH_2CH_3)]Cl

(iii) [Ti(H_2O)6]_3+

(iv) [Co(NH_3)_4Cl(NO_2)]Cl

(v) [Mn(H_2O)6]_2+

(vi) [NiCl_4]_2−

(vii) [Ni(NH_3)_6]Cl_2

(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 - 18 : -
List various types ofisomerism possible for coordination compounds, giving an example of each.

Answer - 18 : -

(a) Geometricisomerism:

This type of isomerism is common inheteroleptic complexes. It arises due to the different possible geometricarrangements of the ligands. For example:

(b) Opticalisomerism:

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

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

Yellow form Red form

(d) Coordinationisomerism:

This type of isomerism arises when theligands are interchanged between cationic and anionic entities of differnetmetal ions present in the complex.

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

(e) Ionizationisomerism:

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

(f) Solvateisomerism:

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

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

Question - 19 : -
How many geometrical isomers are possible inthe following coordination entities?
(i) [Cr(C₂O₄)₃]³⁻ (ii)[Co(NH₃)₃Cl₃]

Answer - 19 : -

(i) For [Cr(C₂O₄)₃]³⁻,no geometric isomer is possible as it is a bidentate ligand.

(ii) [Co(NH₃)₃Cl₃]

Two geometrical isomers are possible.

Question - 20 : -
Draw the structures of optical isomers of:

Answer - 20 : -

(i) [Cr(C_2O_4)_3]_3−

(ii) [PtCl_2(en)_2]_2+

(iii) [Cr(NH_3)_2Cl_2(en)]_+

_Answer

(i) [Cr(C₂O₄)₃]³⁻

(ii) [PtCl₂(en)₂]²⁺

(iii) [Cr(NH₃)₂Cl₂(en)]⁺

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