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GATE 2021 CY – Question 23

Inorganic Chemistry · Transition Metals: Coordination chemistry – structure and isomerism, theories of bonding (VBT, CFT, and MOT). Metal-metal multiple bonds. Energy level diagrams in various crystal fields, CFSE, applications of CFT, Jahn-Teller distortion. Electronic spectra of transition metal complexes: spectroscopic term symbols, selection rules, Orgel and Tanabe-Sugano diagrams, nephelauxetic effect and Racah parameter, charge-transfer spectra. Magnetic properties of transition metal complexes. Ray-Dutt and Bailar twists, Reaction mechanisms: kinetic and thermodynamic stability, associative, dissociative substitution and redox reactions. · 1 mark · Multiple choice

The rate of the substitution reaction of [Co(CN)5Cl]3– with OH– to give [Co(CN)5(OH)]3–

  1. depends on the concentrations of both [Co(CN)5Cl]3– and OH–
  2. depends on the concentration of [Co(CN)5Cl]3– only
  3. is directly proportional to the concentration of OH– only
  4. is inversely proportional to the concentration of OH–

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Correct answer: (B) depends on the concentration of [Co(CN)5Cl]3– only

Explanation

The substitution proceeds by rate-limiting loss of chloride from the cobalt complex, followed by capture of the intermediate by hydroxide. Because the entering ligand participates after the slow step, the rate law is k[Co(CN)5Cl³−] and is independent of hydroxide concentration in this regime.

Therefore **B**; this is a dissociative substitution pattern.