Question answers PYQ chapter 5 Coordination compounds

 Chapter 5                         Coordination Compounds Previous Year Questions 

                                   VSA QUESTIONS (1-MARK QUESTIONS)

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1. Define the term coordination compound.

• Answer: A coordination compound is a compound consisting of a central metal atom or ion bonded to surrounding molecules or ions (called ligands) through coordinate covalent bonds.

2. Write the names of counter ions in (i) Hg[Co(SCN)₄] and (ii) [Pt(NH₃)₄]Cl₂.

• Answer:

  • (i) Counter ions: SCN⁻

  • (ii) Counter ions: Cl⁻

3. Write the oxidation state of nickel in [Ni(CO)₄].

• Answer: Oxidation state of Ni = 0 (since CO is a neutral ligand).

4. What is the coordination number of central atom in [Co(C₂O₄)₃]³⁻?

• Answer: The coordination number is 6 (as each oxalate ion (C₂O₄) is bidentate).

5. What is the coordination number of iron in [Fe(EDTA)]⁻?

• Answer: The coordination number is 6 (EDTA is a hexadentate ligand).

6. Write the name of a complex compound used in chemotherapy.

• Answer: Cis-Platin [Pt(NH₃)₂Cl₂].

7. Name the compound used to estimate the hardness of water volumetrically.

• Answer: EDTA (Ethylenediaminetetraacetic acid).

8. Give the IUPAC name of [PtCl₂(NH₂CH₃)(NH₃)₂]Cl.

• Answer: Ammine(chloro)(methylamine)platinum(II) chloride.

9. How many geometrical isomers are possible for the tetrahedral complex [Ni(CO)₄]?

• Answer: No isomers, as the relative positions of unidentate ligands attached to the central metal atom are the same.

10. Arrange the following in the increasing order of conductivity in solution:

• [Ni(NH₃)₆]Cl₂, [Co(NH₃)₆]Cl₃, and [CoCl₂(en)₂]Cl.

• Answer: [Co(NH₃)₆]Cl₃ > [Ni(NH₃)₆]Cl₂ > [CoCl₂(en)₂]Cl
  (The higher the number of ions dissociated, the higher the conductivity.)

11. Arrange the following ligands in increasing order of ∆ₒ (Crystal field splitting energy) for octahedral complexes:

• Cl⁻, NH₃, I⁻, CO, en.

• Answer: I⁻ < Cl⁻ < NH₃ < en < CO
  (Iodide is weak field, carbon monoxide is a strong field ligand.)

12. Write the IUPAC name of Tollens’ reagent.

• Answer: Silver-ammonia complex or diamminesilver(I) complex.

13. Which is more stable? K₃[Fe(CN)₆] or K₄[Fe(CN)₆]?

• Answer: K₄[Fe(CN)₆] is more stable because of the stronger bond between iron and cyanide.

14. Calculate the overall dissociation equilibrium constant for the [Cu(NH₃)₄]²⁺ ion.

• Given that overall stability constant (β₄) for this complex is 2.1 × 10¹³.

  • Answer: $K_d = 4.7 \times 10^{-14}$

15. What is a chelate ligand? Give one example.

• Answer: A chelate ligand is a ligand that forms more than one bond with the metal ion. Example: EDTA (ethylenediaminetetraacetic acid).

16. Write the IUPAC name of Li[AlH₄].

• Answer: Lithium tetrahydroaluminate.

17. Name one homogeneous catalyst used in hydrogenation of alkenes.

• Answer: Nickel (Ni).

18. Name the types of isomerism shown by coordination entity [CrCl₂(Ox)₂]³⁻.

• Answer: Geometrical isomerism (cis-trans isomerism) and optical isomerism.

19. [Ti(H₂O)₆]Cl₃ is coloured but on heating becomes colourless. Why?

• Answer: The color arises from the d-d transitions in Ti³⁺ (titanium in +3 oxidation state), which gets converted to Ti⁴⁺ (colorless) upon heating.

20. Write the IUPAC name of ionization isomer of [Co(NH₃)₅(SO₄)]Br.

• Answer: Pentaamminenitratocobalt(III) bromide.

21. Write the formula and the name of the coordinate isomer of [Co(en)₃][Cr(CN)₆].

• Answer: Formula: [Cr(en)₃][Co(CN)₆]
  Name: Tris(ethane-1,2-diamine)chromium(III) hexacyanocobaltate(III).

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               SA (I) TYPE QUESTIONS (2-MARK QUESTIONS)

22. Write two differences between a double salt and a coordination compound with the help of an example of each.

• Answer:

  • Double salt: A compound formed by the combination of two salts in a definite proportion, which dissociate into their constituent ions in solution. Example: K₄[Fe(CN)₆].

  • Coordination compound: A complex in which a central metal atom or ion is bonded to surrounding molecules or ions (ligands) via coordinate covalent bonds. Example: [Co(NH₃)₆]Cl₃.

23. Mention the main postulates of Werner’s Theory.

• Answer:

  • Metal ions exhibit two types of valency: primary (linking) and secondary (coordination).

  • Coordination compounds consist of a central metal ion surrounded by ligands.

  • The number of ligands around a metal ion is fixed and specific for each metal.

24. Define (a) Homoleptic and (b) Heteroleptic complexes with the help of one example of each.

• Answer:

  • Homoleptic complex: A complex where all ligands are the same. Example: [Ni(CO)₄].

  • Heteroleptic complex: A complex with different types of ligands. Example: [Co(NH₃)₅Cl]²⁺.

25. In the following coordination entity: [Cu(en)₂]²⁺

• (a) Identify the ligand involved.

• (b) Oxidation state of copper metal.

• Answer:

  • (a) The ligand involved is ethylenediamine (en).

  • (b) Oxidation state of copper is +2.

26. Calculate the magnetic moments of the following complexes:

• (i) [Fe(CN)₆]⁴⁻

• (ii) [CoF₆]³⁻

• Answer: Use the formula $\mu = \sqrt{n(n+2)}$, where n is the number of unpaired electrons.

  • (i) [Fe(CN)₆]⁴⁻: Fe²⁺, 4 unpaired electrons → $\mu = \sqrt{4(4+2)} = \sqrt{24} \approx 4.9 \, \mu_B$.

  • (ii) [CoF₆]³⁻: Co³⁺, 6 unpaired electrons → $\mu = \sqrt{6(6+2)} = \sqrt{48} \approx 6.9 \, \mu_B$.

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27. Explain the following:

• (a) [Fe(CN)₆]³⁻ is an inner orbital complex whereas [FeF₆]³⁻ is an outer orbital complex.

• (b) NH₃ acts as a complexing agent but NH₄⁺ does not.

• Answer:

  • (a) [Fe(CN)₆]³⁻ involves Fe³⁺ with d⁶ configuration, where the ligand (CN⁻) causes pairing of electrons, using the inner d-orbitals. In [FeF₆]³⁻, the fluorine ligands do not cause electron pairing, so the metal uses its outer d-orbitals.

  • (b) NH₃ has a lone pair of electrons to donate and form coordinate bonds with the metal ion, whereas **

NH₄⁺** is a cation with no lone pair available for bonding.