Transition metal and their compounds are used as catalysts in industry and in biological system. For — d and f Block Elements Chemistry Question
Question
Transition metal and their compounds are used as catalysts in industry and in biological system. For example, in the Contact Process, vanadium compounds in the +5 state (V2O5 or VO3^-) are used to oxidise SO2 to SO3 : SO2 + 1/2 O2 $\xrightarrow{\text{V}_2\text{O}_5}$ SO3 It is thought that the actual oxidation process takes place in two stages. In the first step, V5+ in the presence of oxide ions converts SO2 to SO3. At the same time, V5+ is reduced to V4+. 2V5+ + O2- + SO2 $\rightarrow$ 2V4+ + SO3 In the second step, V5+ is regenerated from V4+ by oxygen : 2V4+ + 1/2 O2 $\rightarrow$ 2V5+ + O2- The overall process is, of course, the sum of these two steps : SO2 + 1/2 O2 $\rightarrow$ SO3 [3]
💡 Solution & Explanation
Step 1: Balance the electron transfer between the reduction of persulfate (gains 2e^- per mole) and the oxidation of manganese (loses 5e^- per mole). Step 2: To equate the electrons lost and gained, multiply the reduction half-reaction by 5 and the oxidation half-reaction by 2. This gives: 5S2O8^2- + 10e^- ---> 10SO4^2- and 2Mn^2+ + 8H2O ---> 2MnO4^- + 16H^+ + 10e^-. Step 3: This shows that 5 moles of S2O8^2- are required to oxidize 2 moles of Mn^2+. Therefore, 2.5 moles of S2O8^2- are needed per 1 mole of Mn^2+, which corresponds to option (a).