You are Here: Home

# Redox titratons

Announcements Posted on
TSR's new app is coming! Sign up here to try it first >> 17-10-2016
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.

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

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

### How does exam reform affect you?

From GCSE to A level, it's all changing

### Who would you like to thank?

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.