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Redox titration, determination of iron in iron tablets watch

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    Hey guys, basically tommorow I'm starting my practical investigation and looks like my first experiment is using titration to find the mass of iron in an iron tablet.

    So I have Potassium Permanganate, Sulphuric Acid, Iron tablets.

    Permanganate solution is of known concentration which is 0.001 mol/l, so starting off i dissolve the tablet in sulphuric acid right instead of water, but what volume though?
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    (Original post by Z_Ahmed)
    Hey guys, basically tommorow I'm starting my practical investigation and looks like my first experiment is using titration to find the mass of iron in an iron tablet.

    So I have Potassium Permanganate, Sulphuric Acid, Iron tablets.

    Permanganate solution is of known concentration which is 0.001 mol/l, so starting off i dissolve the tablet in sulphuric acid right instead of water, but what volume though?
    it is your practical investigation; moreover it is your first day at it, take the first day as discovery day, try a variety of different concentration and volume, see what sorts of variables you can change in order to make your results different/no effect? yeah, play around with it, get a QUALITATIVE idea/feel for it.
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    (Original post by Z_Ahmed)
    Hey guys, basically tommorow I'm starting my practical investigation and looks like my first experiment is using titration to find the mass of iron in an iron tablet.

    So I have Potassium Permanganate, Sulphuric Acid, Iron tablets.

    Permanganate solution is of known concentration which is 0.001 mol/l, so starting off i dissolve the tablet in sulphuric acid right instead of water, but what volume though?
    I found using permanganate gave me crap experimental results so hopefully you will do better, I used 20cm^3 but it's worth expermenting. I followed a colorimetric anaylsis technique in the end, I would look up dichromate titrations also.
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    (Original post by TheRabbit)
    I found using permanganate gave me crap experimental results so hopefully you will do better, I used 20cm^3 but it's worth expermenting. I followed a colorimetric anaylsis technique in the end, I would look up dichromate titrations also.
    So I can use like 20 cm3 of sulphuric acid and then 80cm3 of deionised water just to beef up the volume?

    Also now the irons dissolved is the 100cm3 taken to be the v value in the calculation.

    I'm pretty crap with the calculations lol. I have the C value for Permanganate, and using titration I'll get the V value. So using N=c x v i've got number of moles of permanganate. Then from here how do i get the number of moles of Fe??

    Thanks.
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    (Original post by Z_Ahmed)
    So I can use like 20 cm3 of sulphuric acid and then 80cm3 of deionised water just to beef up the volume?

    Also now the irons dissolved is the 100cm3 taken to be the v value in the calculation.

    I'm pretty crap with the calculations lol. I have the C value for Permanganate, and using titration I'll get the V value. So using N=c x v i've got number of moles of permanganate. Then from here how do i get the number of moles of Fe??

    Thanks.
    Yeah it's fine to dilute after it's disolved. Calculation stuff:
    Use N=CV (V in l) to find the number of moles of KMnO4 used. Then you work out the balanced equation (or just remember it as it is a pretty standard equation) then use the relationship 5Fe:KMnO4 so the number of moles of Fe will be 5 times the number of moles of MnO4 ions. Then this concentration multiplied by 0.1 is the conc Fe in moll-1 in your 100cm^3 soloution or multiply the number moles by Fe GFM (55.8g) to find the mass of Fe in the tablet.

    I think an MnO4/Fe titration is one of the Higher PPAs and it's the sort of thing that came up in the Higher exam.
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    (Original post by TheRabbit)
    Well you work out the balanced equation (or just remember it as it is a pretty standard equation) then use the relationship 5Fe:KMnO4 so the concentration of Fe will be 5 times the concentration of MnO4 ions. Then this concentration multiplied by 0.1 is the conc Fe in moll-1 in your 100cm^3 soloution or multiply by Fe GFM (55.8g) to find the Nass of Fe in the tablet.
    Thanks alot, that helped.
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    Okay my notes talk about standardising the KMNO4, but that really isn't necessary because i know it's concentration already. correct?
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    Okay my teacher keeps asking me to find out the exact concentration of sulphuric acid to dissolve the tablet in. What concentrations are recommended?
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    heres the method
    • Grind seven iron tablets then place all the contents into a weighing boat and weigh it.
    • Transfer all contents of the weighing boat to a beaker.
    • After that add 100 ml of deionised water and heat to dissolve the tablets.
    • Leave the solution for around 10-15 mins to cool and once its cool transfer to a 250 ml volumetric flask
    • make up to the mark with deionised water.
    • Prepare 1000 ml of 0.01 mol dm-3 potassium manganate(VII) solution by accurately weighing out approximately 0.01 moles of potassium manganate(VII) and dissolving in 100 ml of 2 mol dm-3 sulphuric acid. This is transferred to a 1000 ml volumetric flask and made up to the mark with deionised water.
    • Pipette a 25 ml aliquot of the potassium manganate(VII) solution into a conical flask
    • Run the unknown iron(II) solution into the flask from a burette.
    • Operate ph meter to find the endpoint.
    • Repeat the titration until concordant results are obtained.
 
 
 
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