In the determination of the amount of iron in a sample, the iron must be in the
ID: 1075867 • Letter: I
Question
In the determination of the amount of iron in a sample, the iron must be in the Fe^2+ state; this is oxidized by the permanganate in the acid solution (H2SO4) to Fe^3+ according to following equation:
MnO4 + 8H + 5Fe^2+ --> Mn^2+ + 5Fe^3+ +4H2O
1.0052g of unknow compound is isolated and analyzed for iron. Its mixed with 20mL of 3M H2SO4 and 3mL of 85% H3PO4. It took 21.5mL KMnO4 solution to titrate iron in sample. KMnO4 solution was as follows: 30mL of stock KMnO4 was mixed with 270mL of distilled water
Calcluate the percentage iron by mass in your unknown iron sample.
mass of iron sample: 1.0052g
volume of KMno4: 21.5mL ; 0.02M solution
Explanation / Answer
MnO4 + 8H + 5Fe^2+ --> Mn^2+ + 5Fe^3+ +4H2O
from equation,
1 mol KMnO4 = 5 mol Fe2+
No of mol of KMnO4 used = 21.5*0.02/1000 = 0.00043 mol
No of mol of Fe2+ reacted in sample = 0.00043*5/1 = 0.00215 mol
mass of iron present in the sample = n*At.wt
= 0.00215*56
= 0.1204 g
percentage iron by mass = weight of iron / weight of sample*100
= 0.1204/1.0052*100
= 12%