An iron nail was dissolved in excess dilute sulphuric acid to produce 100 cm
3 solution. A sample of 10 cm
3 of this solution required 4 x 10
-4 mol of potassium manganate (VII) for complete reaction.
Fe(s) + H
2SO
4 (aq)
Fe
2SO
4 (aq) + H
2 (g)
5Fe
2+ (aq) + MnO
4- Mn
2+ + 4H
2O (l) + 5Fe
3+ (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.