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Question 90 of 91

Q.(i) Write examples of coordination metal complexes in biology.

(ii) Calculate the work done in oxidation of 2 moles of SO2_2 at 298K, if SO2(g)+12O2(g)→SO3(g)SO_{2(g)} + \tfrac{1}{2}O_{2(g)} \rightarrow SO_{3(g)} [Given: R = 8.314 J/K/mol]
Maharashtra MsbshseMaharashtra HSC (MSBSHSE) Board 2026Subjective· 3mImportance★★★★★
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Haemoglobin, chlorophyll and vitamin B12_{12} are biologically vital coordination complexes; for the given reaction, w=−ΔngRT≈2478w = -\Delta n_g RT \approx 2478 J.

(i) Coordination complexes in biology:

  • Haemoglobin — an iron(II) coordination complex in red blood cells, responsible for binding and transporting oxygen.

  • Chlorophyll — a magnesium coordination complex present in plants, essential for photosynthesis.

  • Vitamin B12_{12} (cyanocobalamin) — a cobalt coordination complex, essential for red blood cell formation.

(ii) Work done for SO2(g)+12O2(g)→SO3(g)SO_{2(g)} + \tfrac12 O_{2(g)} \rightarrow SO_{3(g)}, 2 moles of SO2SO_2:

For 1 mole of reaction as written, Δng=1−(1+0.5)=−0.5\Delta n_g = 1 - (1 + 0.5) = -0.5. For 2 moles of SO2SO_2 reacting (i.e. 2× the equation), Δng=2×(−0.5)=−1\Delta n_g = 2\times(-0.5) = -1.

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