You are Here: Home

# Redox titratons Watch

1. Mn04- + 8H+ + 5Fe2+ -------> Mn2= + 5Fe3+ + 4H2O

a multi-vitamin tablet contains vitamins A B C D and iron.
0.325g of a powdered tablet was dissolved in water and a little bit of H2SO4.
12.10 cm3 of 0.002 moldm-3 potassium manganate solution was titrated until permanent pale pink colour was observed.
Calculate the percentage mass of iron in the tablet.

amount og MnO4- = cxv=2.42x10-5 mol
amount og Fe2+= 5 x 2.42 x10-5 = 1.21 x 10-4 mol

so mass is n x M = 1.21 x10-4 x (55.8 x5) = 0.0338
BUT IN THE ANSWER IS DOESNT MULTIPLY THE 55.8 BY 5 AND GIVES THE ANSWER 0.00675 - why do you not x5 when there is 5 moles of Fe2+ ?

0.00675/0.325 = 2.08 %
2. (Original post by asaaal)
Mn04- + 8H+ + 5Fe2+ -------> Mn2= + 5Fe3+ + 4H2O

a multi-vitamin tablet contains vitamins A B C D and iron.
0.325g of a powdered tablet was dissolved in water and a little bit of H2SO4.
12.10 cm3 of 0.002 moldm-3 potassium manganate solution was titrated until permanent pale pink colour was observed.
Calculate the percentage mass of iron in the tablet.

amount og MnO4- = cxv=2.42x10-5 mol
amount og Fe2+= 5 x 2.42 x10-5 = 1.21 x 10-4 mol

so mass is n x M = 1.21 x10-4 x (55.8 x5) = 0.0338
BUT IN THE ANSWER IS DOESNT MULTIPLY THE 55.8 BY 5 AND GIVES THE ANSWER 0.00675 - why do you not x5 when there is 5 moles of Fe2+ ?

0.00675/0.325 = 2.08 %
You've already worked out the number of moles of Fe2+ in relation to the number of moles of MnO4- via the stoichiometric ratio, so you don't need to multiply that by 5 again when working out the mass.

Updated: May 24, 2012
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

It's a dilemma

### How posh are you?

Poll
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.