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Chemistry 5 Marks Questions

Coordination Compounds · Gujarat Board (GSEB) STD 12 Science (GSEB - English Medium). 9 questions.

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Question 15 Marks
What is meant by stability of a coordination compound in solution? State the factors which govern stability of complexes.
Answer
The stability of a complex in a solution refers to the degree of association between the two species involved in a state of equilibrium. Stability can be expressed quantitatively in terms of stability constant or formation constant.

$\text{M}+3\text{L}\leftarrow\rightarrow\text{ML}_{3}$

Stability constant, $\beta=\frac{[\text{ML}_{3}]}{[\text{M}][\text{L}]^{3}}$

For this reaction, the greater the value of the stability constant, the greater is the proportion of ML3 in the solution.

Stability can be of two types:

  1. Thermodynamic stability:

The extent to which the complex will be formed or will be transformed into another species at the point of equilibrium is determined by thermodynamic stability.

  1. Kinetic stability:

This helps in determining the speed with which the transformation will occur to attain the state of equilibrium.

Factors that affect the stability of a complex are:

  1. Charge on the central metal ion: Thegreater the charge on the central metal ion, the greater is the stability of the complex.

  2. Basic nature of the ligand: A more basic ligand will form a more stable complex.

  3. Presence of chelate rings: Chelation increases the stability of complexes.

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Question 25 Marks
 Match the compounds given in Column I with the oxidation state of cobalt present in it (given in Column II) and assign the correct code.

 
Column I (Compound)
 
Column II (Oxidation state of Co)
a.
[Co(NCS)(NH3)5](SO3)
1.
+4
b.
[Co(NH3)4Cl2]SO4
2.
0
c.
Na4[Co(S2O3)3]
3.
+1
d.
[Co2(CO)8]
4.
+2
 
 
5.
+3

Code:

  1. A (1), B (2), C (4), D (5).
  2. A (4), B (3), C (2), D (1).
  3. A (5), B (1), C (4), D (2).
  4. A (4), B (1), C (2), D (3).
Answer
  1. A (5), B (1), C (4), D (2).
 
Column I (Compound)
 
Column II (Oxidation state of Co)
a.
[Co(NCS)(NH3)5](SO3)
5.
+3
b.
[Co(NH3)4Cl2]SO4
1.
+4
c.
Na4[Co(S2O3)3]
4.
+2
d.
[Co2(CO)8]
2.
0

Explanation:

Oxdiation state of CMI (central metal ion) can be calculated by considering the oxidation state of whole molecule is equal to charge present on coordination sphere.

  1. [Co(NCS)(NH3)5]SO3

Let oxidation state of Co be x.

x - 1 + × 0 = +2

x = +2 + 1 = +3

  1. [Co(NH3)4Cl2]SO4

Let oxidation state of Co = x

⇒ x + 4 × 0 + 2 × (-1) = +2

⇒ x - 2 = +2

x = 4

  1. Na4[Co(S2O3)3]

Let oxidation state of Co = x

x + 3 × (-2) = -4

x - 6 = -4

x = -4 + 6 = +2

  1. [Co(CO)8]

Let oxidation state of Co = x

x - 8 × 0 = 0

x = 0

Hence, correct choice is (d).

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Question 35 Marks
 Match the complex species given in Column I with the possible isomerism given in Column II and assign the correct code:

 
Column I (Complex species)
 
Column II (Isomerism)
a.
[Co(NH3)4Cl2]+
1.
Optical
b.
cis-[Co(en)2Cl2]+
2.
Ionisation
c.
[Co(NH3)5 (NO2)]Cl2
3.
Coordination
d.
[Co(NH3)6][Cr(CN)6]
4.
Geometrical
 
 
5.
Linkage

Code:

  1. A (1), B (2), C (4), D (5).
  2. A (4), B (3), C (2), D (1).
  3. A (4), B (1), C (5), D (3).
  4. A (4), B (1), C (2), D (3).
Answer
  1. A (4), B (1), C (2), D (3).
 
Column I (Complex species)
 
Column II (Isomerism)
a.
[Co(NH3)4Cl2]+
4.
Geometrical
b.
cis-[Co(en)2Cl2]+
1.
Optical
c.
[Co(NH3)5 (NO2)]Cl2
2.
Ionisation
d.
[Co(NH3)6][Cr(CN)6]
3.
Coordination

Explanation:

Isomerism in coordination compound is decided by type of ligands and geometry of coordination and arrangement of ligands.

  1. [Co(NH3)4Cl2]+ shows geometrical isomerism due to presence of two types of ligand whose [Co(NH3)4Cl2]+ arrangement around central metal ion.

  1. cis-[Co(en)2Cl2]+ shows optical isomer due to its non-superimposable mirror image relationship.

  1. [Co(NH3)5(NO2)]Cl2 shows ionization isomer due to its interchanging ligand from outside the ionization sphere.
  2. [Co(NH3)6][Cr(CN)6] shows coordination isomer due to interchanging of ligand in between two metal ions from one coordination sphere to another coordination sphere.

Hence, correct choice is (d).

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Question 45 Marks
CoSO4Cl.5NH3 exists in two isomeric forms ‘A’ and ‘B’. Isomer ‘A’ reacts with AgNO3 to give white precipitate, but does not react with BaCl2. Isomer ‘B’ gives white precipitate with BaCl2 but does not react with AgNO3. Answer the following questions.
  1. Identify ‘A’ and ‘B’ and write their structural formulas.
  2. Name the type of isomerism involved.
  3. Give the IUPAC name of ‘A’ and ‘B’.
Answer
CoSO4Cl.5NH3:

  1. Isomer A reacts with AgN03 but not with BaCl2, it shows it has CP ion outside the coordination sphere.

Hence, A = [Co(NH3)5SO4]Cl
Isomer B reacts with BaCl2 but not with AgNO3 , it shows it has SO4- outside the coordination sphere.

Hence, B = [CO(NH3)5Cl]S04

  1. Ionisation isomerism.
  2. A = Pentaamminesulphatocobalt (III) chloride and.

B = Pentaamminesulphatocobalt (III) sulphate.

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Question 55 Marks
Match the complex ions given in Column I with the hybridisation and number of unpaired electrons given in Column II and assign the correct code:
 
Column I (Complex ion)
 
Column II (Hybridisation, number of unpaired electrons)
a.
[Cr(H2O)6]3+
1.
dsp2, 1
b.
[Co(CN)4]2-
2.
sp3d2, 5
c.
[Ni(NH3)6]2+
3.
d2sp3, 3
d.
[MnF6]4-
4.
sp3, 4
 
 
5.
sp3d2, 2
Code:
  1. A (3), B (1), C (5), D (2).
  2. A (4), B (3), C (2), D (1).
  3. A (3), B (2), C (4), D (1).
  4. A (4), B (1), C (2), D (3).
Answer
  1. A (4), B (3), C (2), D (1).
 
Column I (Complex ion)
 
Column II (Hybridisation, number of unpaired electrons)
a.
[Cr(H2O)6]3+
4.
sp3, 4
b.
[Co(CN)4]2-
3.
d2sp3, 3
c.
[Ni(NH3)6]2+
2.
sp3d2, 5
d.
[MnF6]4-
1.
dsp2, 1
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Question 65 Marks
Give the electronic configuration of the following complexes on the basis of Crystal Field Splitting theory.
[CoF6]3-, [Fe(CN)6]4- and [Cu(NH3)6]2+
Answer

According to spectrochemical series related ligands the given complexes can be arranged in a series in the order of increasing field strength as- CN- > NH3 > F-

Thus CN- and NH3 are strong field ligand pair up the t2g electrons before filling eg set.

$[\text{CoF}_6]^{3-},\text{Co}^{3+}(\text{d}^6)\text{t}^4_{2\text{g}}\text{e}^2_\text{g},$

$[\text{Fe}(\text{CN})_6]^{4-},\text{Fe}^{2+}(\text{d}^6)\text{t}^6_{2\text{g}}\text{e}^3_\text{g},$

$[\text{Cu}(\text{NH}_3)_6]^{2+},\ \text{Cu}^{2+}(\text{d}^9)\text{t}^6_{2\text{g}}\text{e}^3_\text{g},$

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Question 75 Marks
Match the complex ions given in Column I with the colours given in Column II and assign the correct code:
 
Column I (Complex ion)
 
Column II (Colour)
a.
[Co(NH3)6]3+
1.
Violet
b.
[Ti(H2O)6]3+
2.
Green
c.
[Ni(H2O)6]2+
3.
Pale blue
d.
[Ni(H2O)4(en)]2+ (aq)
4.
Yellowish orange
 
 
5.
Blue
Code:
  1. A (1), B (2), C (4), D (5).
  2. A (4), B (3), C (2), D (1).
  3. A (3), B (2), C (4), D (1).
  4. A (4), B (1), C (2), D (3).
Answer
  1. A (4), B (1), C (2), D (3).
 
Column I (Complex ion)
 
Column II (Colour)
a.
[Co(NH3)6]3+
4.
Yellowish orange
b.
[Ti(H2O)6]3+
1.
Violet
c.
[Ni(H2O)6]2+
2.
Green
d.
[Ni(H2O)4(en)]2+ (aq)
3.
Pale blue
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Question 85 Marks
Match the coordination compounds given in Column I with the central metal atoms given in Column II and assign the correct code:
 
Column I (Coordination Compound)
 
Column II (Central metal atom)
a.
Chlorophyll
1.
Rhodium
b.
Blood pigment
2.
Cobalt
c.
Wilkinson catalyst
3.
Calcium
d.
Vitamin B12
4.
Iron
 
 
5.
Magnesium
Code:
  1. A (5), B (4), C (1), D (2).
  2. A (3), B (4), C (5), D (1).
  3. A (4), B (3), C (2), D (1).
  4. A (3), B (4), C (1), D (2).
Answer
  1. A (5), B (4), C (1), D (2).
 
Column I (Coordination Compound)
 
Column II (Central metal atom)
a.
Chlorophyll
5.
Magnesium
b.
Blood pigment
4.
Iron
c.
Wilkinson catalyst
1.
Rhodium
d.
Vitamin B12
2.
Cobalt
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Question 95 Marks
Using crystal field theory, draw energy level diagram, write electronic configuration of the central metal atom/ion and determine the magnetic moment value in the following:
  1. $[\text{CoF}_6]^{3-}, [\text{Co(H}_2\text{O})_6]^{2+}, [\text{Co(CN)}_6]^{3-}$
  2. $[\text{FeF}_6]^{3-}, [\text{Fe(H}_2\text{O})_6]^{2+}, [\text{Fe(CN})_6]^{4-}$
Answer
  1.  

$\text{Co}^{2+}=3\text{d}^7$

Number of unpaired electrons = 4

Magnetic moment

$=\sqrt{\text{n}(\text{n}+2)}=\sqrt{4(4+2)}=4.9\text{B.M.}$

$[\text{Co(H}_2\text{O})_6]^{2+}:$

$\text{Co}^{2+}=3\text{d}^7$

Number of unpaired electrons = 3

Magnetic moment = $\sqrt{3(3+2)}=3.87\text{B.M.}$

$[\text{Co(CN)}_6]^{3-}:$

$\text{Co}^{3+}=3\text{d}^6$

Number of unpaired electrons = 0

Diamagnetic.

  1. $\text{FeF}^{3-}_6:$

$\text{Fe}^{3+}=3\text{d}^5$

Number of unpaired electrons = 5

Magnetic moment = $\sqrt{5(5+2})=5.92\text{B.M.}$

$[\text{Fe(H}_2\text{O})_6]^{2+}:$

$\text{Fe}^{2+}=3\text{d}^6$

Number of unpaired electrons = 4

Magnetic moment = $\sqrt{4(4+2})=4.9\text{B.M.}$

$[\text{Fe(CN)}_6]^{4-}:$

$\text{Fe}^{2+}=3\text{d}^6$

Diamagnetic.

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