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% of iron in iron tablets? OCR chem

So this is the redox equation provided
5fe2+ + MnO4- + 8H+ --> 5Fe3+ + Mn2+ + 4H20
So 25cm3 of a 100cm3 solution of FeSO4 is titrated against 0.02moldm-3 of 8.60cm3 of MnO4-
So I calculated mol of mno4- and got 1.72x10-4 and multiplied this by 5 to get mOles of FeSO4
My teacher said to calculate mass of the 100cm3 solution and using the mass of the iron tablets (1.16g) and then do mass/mass of the iron tablets but I'm really confused as to how the mass of the 100cm3 solution divided by the mass of the iron tablets tells you the percentage? Can anyone explain?
(edited 8 years ago)
Reply 1
Avatar for AqsaMx
AqsaMx
OP
5
Original post by AqsaMx
So this is the redox equation provided
5fe2+ + MnO4- + 8H+ --> 5Fe3+ + Mn2+ + 4H20
So 25cm3 of a 100cm3 solution of FeSO4 is pipettes again 0.02moldm-3 of 8.60cm3 of MnO4-
So I calculated mol of mno4- and got 1.72x10-4 and multiplied this by 5 to get mOles of FeSO4
My teacher said to calculate mass of the 100cm3 solution and using the mass of the iron tablets (1.16g) and then do mass/mass of the iron tablets but I'm really confused as to how the mass of the 100cm3 solution divided by the mass of the iron tablets tells you the percentage? Can anyone explain?


The final answer is 16.6% btw
Reply 2
Avatar for AqsaMx
AqsaMx
OP
5
Anyone?
Reply 3
Avatar for Rick_G
Rick_G
100cm3 is the intial volume.

moles of Fe in 25cm3 = 8.6x10-4 moles
moles Fe in 100cm3 = (8.6x10-4) x 4 = 3.44x10-3
mass of Fe = moles x mr = (3.44x10-3) x 55.8 = 0.192 grams
% mass = mass Fe/mass tablets x 100 = 0.192/ 1.16 x 100 = 16.54%
Reply 4
Avatar for Rick_G
Rick_G
lool i realised im 3 weeks late

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