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Redox titratons

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    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 %
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    (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.

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Updated: May 24, 2012
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