Results are out! Find what you need...fast. Get quick advice or join the chat
Hey! Sign in to get help with your study questionsNew here? Join for free to post

Redox titratons

Announcements Posted on
Will you get the grades you need for uni? Get prepared today and de-stress, sign up to email alerts for course places! 02-06-2015
Waiting on IB results? Our IB results hub explains everything you need to know 01-06-2015
  1. Offline

    ReputationRep:
    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. Offline

    ReputationRep:
    (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.

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  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
    your full birthday is required
  1. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide to join now Processing…

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.

New on TSR

It's IB results day tomorrow

Check out our IB results hub here & get prepared here

Study resources
x

Think you'll be in clearing or adjustment?

Hear direct from unis that want to talk to you

Get email alerts for university course places that match your subjects and grades. Just let us know what you're studying.

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