If the number of moles of Fe2+ ions oxidised by one mole of acidified MnO4−is x, the number of moles of Fe2+ ions oxidised by one mole of acidified Cr2O72− is
The reactions that happen are: MnO4−+5e−‌→Mn2+‌‌(1‌ mole of ‌MnO4−‌takes ‌5‌ electrons ‌) Cr2O72−+14H++6e−‌→2Cr3++7H2O‌‌(1‌ mole of ‌Cr2O72−‌ takes ‌6‌ electrons ‌) Fe2+‌→Fe3+‌‌(‌ Each ‌Fe2+‌ loses ‌1‌ electron. ‌) Step 1: How many Fe2+ ions does 1 mole of MnO4‌−oxidize? 1 mole of MnO4‌−can take in 5 electrons. Each Fe2+ gives up 1 electron to get oxidized. So, 1 mole of MnO4‌−can oxidize 5 moles of Fe2+. This number is called x. Step 2: How many Fe2+ ions does 1 mole of Cr2O7‌2− oxidize? 1 mole of Cr2O72− can take in 6 electrons. That means it can oxidize 6 moles of Fe2+. Step 3: What is the answer in terms of x ? Since x=5, and Cr2O7‌2− can oxidize 6 moles, the answer is ‌