Coordination Compounds Quiz - ICSE Class 12 Chemistry

Free practice quiz: Coordination Compounds (ICSE Class 12 Chemistry). 61 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

Sample questions

1. Which of the following complexes exhibits the highest crystal field stabilization energy (CFSE) in an octahedral field?

   1. [Co(NH3)6]3+
   2. [Co(CN)6]3-
   3. [Co(H2O)6]3+
   4. [Co(en)3]3+
   Show answer

   Answer: B. [Co(CN)6]3-

   The crystal field stabilization energy (CFSE) depends on the spectrochemical series. CN- is a strong field ligand, NH3 and en are moderate field ligands, and H2O is a weak field ligand. Strong field ligands cause a larger splitting of d-orbitals (Δo), leading to higher CFSE. For d6 Co(III) complexes, the CFSE is -2.4 Δo for low spin and -0.4 Δo for high spin. [Co(CN)6]3- is a low spin complex with a strong ligand, resulting in the largest Δo and thus the highest CFSE.

2. A complex exhibits optical activity if it is chiral. Which of the following complexes is chiral?

   1. [Co(en)2Cl2]+
   2. [Co(NH3)4Cl2]+
   3. [Co(en)3]3+
   4. [Cr(NH3)6]3+
   Show answer

   Answer: A. [Co(en)2Cl2]+

   Chirality in coordination complexes often arises from the arrangement of ligands. For [Co(en)2Cl2]+, geometrical isomers exist: cis and trans. The cis isomer of [Co(en)2Cl2]+ is chiral and exists as a pair of enantiomers, hence it is optically active. The trans isomer has a plane of symmetry and is achiral. [Co(NH3)4Cl2]+ has cis and trans isomers, but neither is chiral. [Co(en)3]3+ and [Cr(NH3)6]3+ are octahedral complexes with all ligands identical or arranged symmetrically such that they possess planes of symmetry and are achiral.

3. Which of the following statements about coordination number is correct?

   1. It is always equal to the number of ligands.
   2. It is the number of ions surrounding the central metal ion.
   3. It is the number of direct coordinate bonds formed by the central metal ion with ligands.
   4. It is equal to the oxidation state of the central metal ion.
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   Answer: C. It is the number of direct coordinate bonds formed by the central metal ion with ligands.

   The coordination number of a central metal ion in a complex is defined as the number of sigma bonds formed between the central metal ion and the ligands. It is not necessarily equal to the number of ligands (as polydentate ligands count differently) or the number of ions surrounding it. It is also distinct from the oxidation state.

4. The oxidation state of nickel in K2[Ni(CN)4] is:

   1. 0
   2. +1
   3. +2
   4. +4
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   Answer: C. +2

   Let the oxidation state of Nickel be x. The complex is neutral, so the sum of oxidation states is zero. 2(+1) (for K) + x (for Ni) + 4(-1) (for CN) = 0 => 2 + x - 4 = 0 => x - 2 = 0 => x = +2. Therefore, the oxidation state of Nickel is +2.

5. What is the correct IUPAC name for Na[AuCl4]?

   1. Sodium tetrachloroaurate(III)
   2. Sodium tetrachlorogold(III)
   3. Sodium tetrachloroaurate(I)
   4. Gold sodium tetrachloride
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   Answer: A. Sodium tetrachloroaurate(III)

   The cation is sodium (Na+). The complex anion is [AuCl4]-. The metal is gold, and in anionic complexes, it is called 'aurate'. The ligands are chloro. There are four chloro ligands, hence 'tetrachloro'. To find the oxidation state of Au: +1 (for Na) + x (for Au) + 4(-1) (for Cl) = 0 => 1 + x - 4 = 0 => x = +3. So, the name is Sodium tetrachloroaurate(III). 'Gold' is used for cationic complexes, 'aurate' for anionic.

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