MnO2 is the most important oxide of manganese. MnO2 occurs naturally as the black coloured mineral p — d and f Block Elements Chemistry Question
Question
MnO2 is the most important oxide of manganese. MnO2 occurs naturally as the black coloured mineral pyrolusite. It is an oxidising agent, and decomposes to Mn3O4 on heating to 530°C. It is used in the preparation of potassium permanaganate and in the production of Cl2 gas. Over half a million tonnes per year of MnO2 is used in dry batteries. [3, 4]
💡 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).