Questions - Answers

2 Marks

1. CuSO₄ . 5 H₂O is blue in colour where as anhydrous CuSO4 is colourless. Why?
A: CuSO₄ . 5 H₂O has 5 ligands (H₂O molecules). These ligands cause splitting of d-orbitals & d-d transition of the unpaired d-electron. So CuSO₄ . 5 H₂O is blue in colour where as anhydrous CuSO₄ has no ligands and is colourless.
 

2. How many moles of AgCl are produced on addition of AgNO₃ solution to
a) CoCl₃ . 5 NH₃ b) CoCl₃ . 6 NH₃
A: a) CoCl₃ . 5 NH₃ = [Co(NH₃)₅Cl]Cl₂
It has 2 ionizable Cl^-  ions and produce 2 moles of AgCl.
b) CoCl₃ . 6 NH₃ = [Co(NH₃)₆]Cl₃
It has 3 ionizable Cl^-  ions and produce 3 moles of AgCl.

3. Why Zn⁺² is diamagnetic where as Mn⁺² is paramagnetic?
A: Zn⁺² = [Ar]₃d_¹⁰ 
Due to absence of unpaired d-electrons in Zn⁺², it is diamagnetic.
Mn⁺² = [Ar]₃d_⁵
Due to presence of unpaired d-electrons (5) in Mn⁺², it is paramagnetic.
 

4. Aqueous Cu⁺² ions are blue in colour whereas aqueous Zn⁺² ions are colourless. Why?
A: Cu⁺² = [Ar]4s⁰3d⁹
     Zn⁺² = [Ar]4s⁰ 3d¹⁰
Due to presence of one unpaired d-electron in 3d sub shell of Cu⁺², due to d-d transition, it absorbs yellow colour and transmits blue colour. So aqueous Cu⁺² ions are blue in colour. As Zn⁺² does not contain unpaired d electrons aqueous Zn⁺² ions are colourless.
 

5. Calculate spin only magnetic moment of Fe⁺² (aq.) ion.
A: Fe⁺² = [Ar]₃d⁶   
 Fe⁺² has 4 unpaired d-electrons (n)

6. Calculate the magnetic moment of a divalent ion in aqueous solution, if its atomic number is 25.

7. Predict which of the ions Cu⁺, Sc⁺³, Mn⁺², Fe⁺² are coloured in aqueous solution? Give reasons.
A: Cu⁺ has [Ar] 3d¹⁰, Sc⁺³ has [Ar] 3d0 configurations and both are colourless due to pairing of all the d-electrons in Cu⁺, no d-electrons in Sc⁺3.
Mn⁺² has [Ar] 3d⁵, Fe⁺² has [Ar] 3d⁴ configurations and both are coloured due to presence of unpaired d-electrons, which causes d-d transition.

9. What is meant by disproportionation of an oxidation state? Give an example.
A: When the same element exhibit 3 different oxidation states in a redox reaction, the reaction is said to be disproportion reaction. One oxidation state is unstable (middle oxidation state) compared to other 2 oxidation states (lower and higher oxidation states) in a reaction is called disproportion of oxidation state.

( 2 NH₃ groups are adjacent to each other) (2 NH₃ groups are opposite to each other)
 

11. What is meant by disproportionation of an oxidation state? Give an example.
Ans: When the same element exhibit 3 different oxidation states in a redox reaction, the reaction is said to be disproportion reaction. One oxidation state is unstable (middle oxidation state) compared to other 2 oxidation states (lower and higher oxidation states) in a reaction is called disproportion of oxidation state.
         
         

12. What is the difference between a double salt and a complex compound?
A: Double salt: A salt formed by physical union of 2 salts and lose its identity in solution and gives test for all the ions present in it.

Complex compound: A compound formed by chemical union of 2 salts and does not lose its identity in solution.

4 Marks

1. Write the important postulates of Werner's theory of complex compounds.
A: Werner's Theory: Alfred Werner gave satisfactory explanation to the mechanism of formation of complex compounds.
Important postulates:
* Every complex compound has central metal atom (or ion)
* It shows 2 types of valencies.
* Primary valency: It is equal to oxidation state of the central atom. It is ionizable valency. These valencies are non directional and represented by dotted line..........
* Secondary valency: It is equal to coordination number of metal atom in the complex. It is non ionizable valency. These valencies are directional and represented by thick line _______.
* Negative ligands may satisfy both primary and secondary valencies in some complexes.

3. What is meant by 'Lanthanide contraction'? Give the consequences of it.
A: Lanthanide Contraction: The gradual decrease in atomic size, ionic size, of 14 lanthanide elements due to diffused shape of 'f' orbitals and poor shielding of valence electrons is known as "Lanthanide contraction".
Consequences: Properties of 4d & 5d elements are similar. It is difficult to separate lanthanides from their mixture due to similar crystal structure and properties.
 

4. Define "Effective Atomic Number" (EAN). Calculate the EAN of metals in the complexes
a) K₄[Fe(CN)₆]            (b) [Co(H₂O)₆] (NO₃]₃
Ans: "Effective atomic number (EAN) is the total number of electrons possessed by the
central metal atom in a complex, after coordination".
EAN = Z - no. of e^- lost by the metal atom + no. of e^- gained from the ligands.
e.g.: (i) EAN of Fe in K₄ [Fe(CN)₆]
   EAN = 26 - 2 + (6 × 2) = 24 + 12 = 36
   (ii) EAN of Co in [Co(H₂O)6] (NO₃)₃
    EAN = 27 - 3 + (6 × 2) = 24 + 12 = 36

5. Write 4 characteristic properties of transition elements.
A: * They form alloys, coloured compounds.
     * They form complex compounds.
     * They exhibit variable oxidation states.
      * They acts as catalyst.
 

6. Give 4 applications of co-ordination compounds in different fields.
A:  * Hardness of water is esitmated by titration with Na₂ EDTA.
* Fixing of photography by the formation of  
* Wilkinson catalyst [(Ph₃P)₃ RhCl] is used for the Hydrogenation of alkenes.
* EDTA is used in the treatment of lead poisoning.
 

7. Write the formulae of the following by using IUPAC norms.
a) Tetra hydroxo zincate (II)
b) Hexa ammine cobalt (III) sulphate
c) Potassium tetra chloro palladate (II)
d) Potassium tri (oxalato) chromate (III)

A: a)        b) [Co(NH₃)₆]₂(SO₄)₃         c) K₂[PdCl₄]           d) K₃[Cr(C₂O₄)₃]
 

8. Write the systematic names of the following by using IUPAC norms.
a) [Co(NH₃)₆]Cl₃                     b) [Pt(NH₃)₂Cl(NH₂CH₃)]Cl

Ans: a) Hexa ammine cobalt (III) chloride
b) Diammine chloro (methyl amino) Platinum (II) chloride
c) Hexa aqua titanium (III) ion
d) Tetra chloro Nickelate (II) ion
 

9. Explain different types of structural isomerism exhibited by coordination compounds giving suitable examples.
Ans: The isomerism that arises due to the difference in structure (due to different arrangement of atoms) of two complex compounds is called structural isomerism.
      This isomerism further classified into
a) Linkage isomerism: This type of isomerism arises when the ambidenate ligand present in a complex act as isomers (bond through different atoms).
e.g.: [Co(NH₃)₅ NO₂]Cl₂ & [Co(NH₃)₅ ONO]Cl₂
b) Co-ordination isomerism: This type of isomerism arises from the interchange of ligands between two metal atoms belong to two complex compounds.
e.g.: [Co(NH₃)₆] [Cr(CN)₆] & [Co(CN)₆] [Cr(NH₃)₆]
c) Ionisation isomerism: This type of isomerism arises when the compounds having same stoichiometric composition but give different ions in solution.
e.g.: [Co(NH₃)₅ SO₄]Br & [Co(NH₃)5 Br]SO₄
d) Hydrate isomerism: This type of isomerism arises when the complex compounds having H₂O molecules present as ligands (inside of the co-ordination sphere) and as free molecules (present outside of the co-ordination sphere).
e.g.: [Cr(H₂O)₆]Cl₃ (Violet) & [Cr(H₂O)₅Cl]Cl₂ . H₂O (grey - green)
 

10. Explain different types of sterio isomerism exhibited by coordination compounds giving suitable examples.
Ans: The isomerism that arises due to different spacial arrangements of ligands around the metal atom or ion is called stereo isomerism. This isomerism further classified into
a) Geometrical isomerism: This type of isomerism arises due to different geometric arrangements of the ligands (in the space) when 2 identical ligands occupy adjacent positions, the isomer is called "Cis" and arranged opposite to one another, the isomer is called "trans" isomer.

In octahedral complex, fac (same ligands occupy adjacent positions at the corners of tetrahedron) and mer (same ligands occupy around the meridian of the octahedron) isomers are possible.

 

b) Optical isomerism: This type of isomerism arises due to the rotation of plane polarised light by a chiral complex.

 If the light is rotated towards right side is called "dextro" isomer, towards left side is called "laevo" isomer.

11. What are homoleptic and heteroleptic complexes? Give suitable examples.
A: Homoleptic complex is the complex in which central metal is bound by one kind of ligands.

      Heteroleptic complex is the complex in which central metal atom is bound by different (two or more than two) types of ligands.