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: The conversion between chromate (CrO4^2-) and dichromate (Cr2O7^2-) is pH-dependent. Chromate is stable in basic/neutral conditions, while dichromate is stable in acidic conditions. Step 2: Increasing acidity (lowering pH to an acidic value, x < 7, e.g., 6) converts yellow chromate to orange dichromate: 2CrO4^2- + 2H+ <=> Cr2O7^2- + H2O. Conversely, adding base (raising pH to a basic value, y > 7, e.g., 8) shifts the equilibrium back to chromate. Step 3: Thus, x must be acidic (6) and y must be basic (8), which corresponds to option (a).