An iron nail was dissolved in excess dilute sulphuric acid to produce 100 cm3 solution. A sample of 10 cm3 of this solution required 4 x 10-4 mol of potassium manganate (VII) for complete reaction.

Fe(s) + H2SO4 (aq) Fe2SO4 (aq) + H2 (g)

5Fe2+ (aq) + MnO4- Mn2+ + 4H2O (l) + 5Fe3+ (aq)

If the mass of nail used was 1.45g, calculate the number of moles of Fe2+ produced in the reaction.

The solution they gave was simple:

5 x (4 x 10-4) x 10

= 0.02 mol.

But I don't understand. If 1 mol of MnO4 requires 5 mol of Fe2+, wouldn't it mean that 1 mol of Fe 2+ uses 1/5 mol of MnO4 to produce 1 mol of Fe3+? So, shouldn't it be 4 x 10-4 / 5 instead of 4 x 10-4 x 5?

Also, why do they need to x 10?

My solution was 1.45 / 56 = 0.03 mol since 1 mol of Fe require 1 mol of H2SO4 to produce 1 mol of FeSO4. Why is this not accepted? Thanks.