Chapter 9: Coordination Compounds Mock Test
Time: 1 Hour | Maximum Marks: 25
- All questions are compulsory.
- Section A contains Q1 (Multiple Choice) and Q2 (Very Short Answer).
- Section B contains Short Answer Type I questions (2 marks each). Attempt any 4.
- Section C contains Short Answer Type II questions (3 marks each). Attempt any 2.
- Section D contains Long Answer questions (4 marks each). Attempt any 1.
SECTION A
Q1. Select and write the most appropriate answer from the given alternatives: [4 Marks]
-
The geometry of a complex with a coordination number of 6 is generally:
(A) Tetrahedral(B) Square planar(C) Octahedral(D) Trigonal bipyramidal
-
The oxidation state of Cobalt (Co) in the complex $[Co(NH_3)_5Cl]Cl_2$ is:
(A) +2(B) +3(C) +4(D) +1
-
Calculate the Effective Atomic Number (EAN) of Iron (Z=26) in $[Fe(CN)_6]^{4-}$:
(A) 36(B) 35(C) 34(D) 33
-
The complexes $[Co(NH_3)_5SO_4]Br$ and $[Co(NH_3)_5Br]SO_4$ are examples of:
(A) Linkage isomerism(B) Coordination isomerism(C) Ionization isomerism(D) Optical isomerism
Q2. Answer the following questions in one sentence: [3 Marks]
- Define: Ambidentate ligand.
- Write the IUPAC name of the complex $K_3[Fe(C_2O_4)_3]$.
- What is meant by a homoleptic complex?
SECTION B
Attempt any FOUR of the following: [8 Marks]
- State any two postulates of Werner's theory of coordination compounds.
- Distinguish between a double salt and a coordination complex. (Write 2 points).
- Calculate the Effective Atomic Number (EAN) of Copper in $[Cu(NH_3)_4]^{2+}$. (Atomic number of Cu = 29).
- Define geometric isomerism. Draw the *cis* and *trans* isomers of $[Pt(NH_3)_2Cl_2]$.
- What are polydentate ligands? Give one example with its structural formula or composition.
SECTION C
Attempt any TWO of the following: [6 Marks]
- On the basis of Valence Bond Theory (VBT), explain the geometry and magnetic property of the $[NiCl_4]^{2-}$ complex. (Atomic number of Ni = 28).
- Define optical isomerism in coordination compounds. Draw the optical isomers (enantiomers) of the complex ion $[Co(en)_3]^{3+}$.
- Explain linkage isomerism and coordination isomerism with one example for each.
SECTION D
Attempt any ONE of the following: [4 Marks]
- (a) Discuss the structure and magnetic property of $[CoF_6]^{3-}$ on the basis of Valence Bond Theory. (Atomic number of Co = 27). [3 Marks]
(b) Define: Coordination Number. [1 Mark] - (a) Write the IUPAC names for the following complexes: (i) $[Pt(NH_3)_2Cl_2]$ and (ii) $Na_3[Co(NO_2)_6]$. [2 Marks]
(b) Explain the terms: (i) Coordination sphere (ii) Ligand. [2 Marks]
Solutions & Marking Scheme
SECTION A [7 Marks]
Q1. Multiple Choice Answers:
1. (C) Octahedral [1 Mark for correct option]
2. (B) +3 [1 Mark. $x + 5(0) + (-1) = +2 \implies x = +3$]
3. (A) 36 [1 Mark. EAN = 26 - 2 + (6 × 2) = 36]
4. (C) Ionization isomerism [1 Mark. They yield different ions in solution]
Q2. Very Short Answers:
1. Ambidentate ligand:
A ligand that has two different donor atoms and can coordinate to the central metal atom/ion through either of the two atoms is called an ambidentate ligand (e.g., $NO_2^-$, $SCN^-$). [1 Mark for definition]
2. IUPAC Name of $K_3[Fe(C_2O_4)_3]$:
Potassium trioxalatoferrate(III). [1 Mark for correct name]
3. Homoleptic complex:
A complex in which the central metal atom or ion is bound to only one kind of donor group (ligand) is called a homoleptic complex. [1 Mark for definition]
SECTION B [8 Marks]
Q3. Werner's Theory Postulates:
- Most elements exhibit two types of valencies: Primary valency (ionizable, corresponds to oxidation state) and Secondary valency (non-ionizable, corresponds to coordination number). [1 Mark]
- Every central metal atom tends to satisfy both its primary and secondary valencies. [1 Mark]
- Secondary valencies are highly directional and dictate the definite geometry of the complex. (Any two points accepted)
Q4. Double salt vs Coordination complex:
| Double Salt | Coordination Complex |
|---|---|
| Dissociates completely into simple constituent ions in an aqueous solution. | Does not dissociate completely; the complex ion retains its identity in solution. |
| Loses its identity in the dissolved state. | Retains its solid-state identity even in dissolved state. |
[1 Mark for each point of distinction. Total 2 Marks]
Q5. EAN Calculation for $[Cu(NH_3)_4]^{2+}$:
Atomic number of Cu ($Z$) = 29. [1/2 Mark]
Oxidation state of Cu ($X$): $x + 4(0) = +2 \implies X = 2$. [1/2 Mark]
Electrons from 4 $NH_3$ ligands ($Y$) = $4 \times 2 = 8$. [1/2 Mark]
EAN = $Z - X + Y = 29 - 2 + 8 = 35$. [1/2 Mark for correct answer]
Q6. Geometric Isomerism and Isomers of $[Pt(NH_3)_2Cl_2]$:
Definition: Isomerism arising due to different spatial arrangements of ligands around the central metal atom in heteroleptic complexes is called geometric isomerism (cis-trans isomerism). [1 Mark]
Cis-isomer [1/2 M]
Trans-isomer [1/2 M]
Q7. Polydentate Ligands:
A ligand that has two or more donor atoms and can bind to the central metal ion simultaneously through multiple coordination sites is called a polydentate ligand. [1 Mark]
Example: EDTA (Ethylenediaminetetraacetate) is a hexadentate ligand. It coordinates through 2 Nitrogen atoms and 4 Oxygen atoms. [1 Mark for example]
SECTION C [6 Marks]
Q8. VBT for $[NiCl_4]^{2-}$:
1. Oxidation state of Ni is +2. Electronic configuration of Ni ($Z=28$) is $[Ar] 3d^8 4s^2$.
Configuration of $Ni^{2+}$ is $[Ar] 3d^8$. [1 Mark]
2. Nature of Ligand: $Cl^-$ is a weak field ligand. It cannot force the pairing of the two unpaired 3d electrons against Hund's rule. The inner 3d orbitals remain unavailable. [1 Mark]
3. Hybridization & Geometry: To accommodate 4 pairs of electrons from 4 $Cl^-$ ligands, $Ni^{2+}$ uses one 4s and three 4p orbitals, undergoing $sp^3$ hybridization. The geometry is Tetrahedral. [1/2 Mark]
4. Magnetic Property: Since there are 2 unpaired electrons present in the 3d subshell, the complex is Paramagnetic. [1/2 Mark]
Q9. Optical Isomerism and $[Co(en)_3]^{3+}$:
Definition: Complexes that are non-superimposable mirror images of each other are called optical isomers or enantiomers. They rotate the plane of polarized light in opposite directions (dextro and laevo). [1 Mark]
Enantiomers of $[Co(en)_3]^{3+}$:
Draw an octahedral Co center with three bidentate 'en' ligands curving between adjacent vertices, and its mirror image. [2 Marks for drawing both enantiomers correctly]
Mirror Image 1
Mirror Image 2
Q10. Linkage and Coordination Isomerism:
1. Linkage Isomerism: Occurs in complexes containing ambidentate ligands. The isomers differ in the donor atom through which the ligand is attached to the metal. [1 Mark]
Example: $[Co(NH_3)_5(NO_2)]^{2+}$ (yellow, N-bonded) and $[Co(NH_3)_5(ONO)]^{2+}$ (red, O-bonded). [1/2 Mark]
2. Coordination Isomerism: Occurs when both cation and anion are complex ions. It arises due to the interchange of ligands between the cationic and anionic entities. [1 Mark]
Example: $[Co(NH_3)_6][Cr(CN)_6]$ and $[Cr(NH_3)_6][Co(CN)_6]$. [1/2 Mark]
SECTION D [4 Marks]
Q11. (a) VBT for $[CoF_6]^{3-}$ [3 Marks] (b) Coordination Number [1 Mark]
(a) Structure and Magnetic Property of $[CoF_6]^{3-}$:
1. Oxidation state of Co = +3. $Co^{3+}$ configuration is $[Ar] 3d^6$. [1 Mark]
2. $F^-$ is a weak field ligand. It does not cause pairing of the 3d electrons. Thus, 4 unpaired electrons remain in the 3d subshell. [1 Mark]
3. Since inner 3d orbitals are unavailable, $Co^{3+}$ uses its outer orbitals (one 4s, three 4p, and two 4d) undergoing $sp^3d^2$ hybridization. The geometry is Octahedral. Because it has 4 unpaired electrons, the complex is highly Paramagnetic (outer orbital/high spin complex). [1 Mark]
(b) Coordination Number: The total number of coordinate bonds formed between the ligands and the central metal atom/ion. [1 Mark]
Q12. (a) IUPAC Names [2 Marks] (b) Terms [2 Marks]
(a) IUPAC Names:
- (i) $[Pt(NH_3)_2Cl_2]$: Diamminedichloroplatinum(II) [1 Mark]
- (ii) $Na_3[Co(NO_2)_6]$: Sodium hexanitrocobaltate(III) [1 Mark]
(b) Explanation of terms:
- (i) Coordination Sphere: The central metal atom/ion and the ligands directly attached to it are enclosed in square brackets. This collectively constitutes the coordination sphere, which acts as a single non-ionizable unit. [1 Mark]
- (ii) Ligand: An atom, ion, or molecule that can donate at least one pair of electrons to the central metal atom to form a coordinate bond. [1 Mark]
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