JEE Advanced levelSingle correct optionDifficulty 3 of 3df037
In weakly alkaline medium MnOX4X− oxidises IX− to IOX3X− and is itself reduced to MnOX2. The mass of KMnOX4 (molar mass 158gmol−1) required to oxidise 0.05 mol of KI in this medium is
A31.6g
B9.48g
C7.90g
D15.8g
Answer: D
Mn changes from +7 to +4 (3 electrons per MnOX4X−) while I changes from −1 to +5 (6 electrons), so 2 mol MnOX4X− per mol IX−: 2MnOX4X−+IX−+HX2O2MnOX2+IOX3X−+2OHX− (balanced in atoms and charge). Moles = 0.05×2=0.10, mass = 0.10×158=15.8g. The 9.48 g option wrongly uses the acidic 5-electron change.