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AIIMS UG Chemistry — practice by topic

Browse 43 questions across 3 Chemistry topics. Choose what you want to revise, then open a question to check its answer and worked solution.

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Chemistry topics

Coordination Compounds (43)d- and f-Block Elements (8)The d- and f-Block Elements (8)

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1 mol of CoCl₃·4NH₃ (green or violet) gives how many moles of AgCl?Read the answer and worked solution →In a coordination compound, the central metal atom/ion is best classified as a:Read the answer and worked solution →In the coordination compound K₃[Fe(CN)₆], the coordination sphere is:Read the answer and worked solution →In [Ni(CO)₄], the oxidation state of Ni is:Read the answer and worked solution →

Worked practice questions

1 mol of CoCl₃·4NH₃ (green or violet) gives how many moles of AgCl?

  1. 2
  2. 1
  3. 3
  4. 0
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Correct answer: B. 1

CoCl₃·4NH₃ = **[CoCl₂(NH₃)₄]Cl**, a 1:1 electrolyte. Only 1 Cl⁻ is outside the coord sphere → **1 mol AgCl**. The other 2 Cl⁻ are coordinated to Co. Green and violet are *cis*/*trans* geometrical isomers.

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In a coordination compound, the central metal atom/ion is best classified as a:

  1. Arrhenius base
  2. Lewis acid (electron pair acceptor)
  3. Brønsted acid
  4. Lewis base
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Correct answer: B. Lewis acid (electron pair acceptor)

Central metal atom/ion accepts electron pairs from ligands → **Lewis acid**. Ligands donate electron pairs → **Lewis bases**. The bond is a coordinate (dative) bond.

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In the coordination compound K₃[Fe(CN)₆], the coordination sphere is:

  1. Fe³⁺
  2. CN⁻ only
  3. K₃
  4. [Fe(CN)₆]³⁻
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Correct answer: D. [Fe(CN)₆]³⁻

**Coordination sphere** = central atom + ligands within the square brackets = **[Fe(CN)₆]³⁻**. K⁺ is the **counter ion** (outside the brackets). The coordination number of Fe³⁺ is 6.

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