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    So I'm carrying out a titration to determine the concentration of iron in iron tablets. I crushed about 5 tablets and dissolved them in sulfuric acid (1 M) before transferring it to a 100 ml volumetric flask, along with the rinsings. I made it up to the mark using deionised water and inverted the flask a couple of times. When it came to the titration, no matter how much potassium permanganate I used (0.005M), I never got a permanent colour change. The colour kept reverting back to colourless within 10 to 20 seconds. Idk whats wrong, I tried changing tablets and still I got the same thing. Someone help pls.
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    dw!!!! I did this practical this week and you won’t acc get a permanent colour change. Basically you have to put the KMNO4 in until the solution goes pink, but upon standing the pink colour WILL fade. This is because the manganate and the iron ions have a reaction that turns the solution colourless again. As soon as you see the solution turn pink, you record your titre. On my practical sheet it did say ‘add potassium manganate until the solution turns pink, and upon standing the pink colour disappears’ so dw about it. The reaction will happen anyways, meaning no matter how much manganate you add, the iron sulfate and potassium manganate solution will eventually revert to colourless. Hope I helped Xx
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    (Original post by ahfae)
    So I'm carrying out a titration to determine the concentration of iron in iron tablets. I crushed about 5 tablets and dissolved them in sulfuric acid (1 M) before transferring it to a 100 ml volumetric flask, along with the rinsings. I made it up to the mark using deionised water and inverted the flask a couple of times. When it came to the titration, no matter how much potassium permanganate I used (0.005M), I never got a permanent colour change. The colour kept reverting back to colourless within 10 to 20 seconds. Idk whats wrong, I tried changing tablets and still I got the same thing. Someone help pls.
    Do you know the approximate percentage of iron in the tablets? Could you look some standard values up? Can you then do the calculations to work out the approximate expected volume of KMnO4 that you should need?

    When you do the practical and you add your calculated estimate and you get a pink colour, like Soveryanonymous says, take that as your endpoint, even if the colour reverts to colourless.

    When you say "no matter how much", what sort of volume are we talking? Have you tried one drop of your iron solution and add dropwise the KMnO4 solution. I'll bet that when the manganate is in large excess it'll be pink/purple.
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    (Original post by Soveryanonymous)
    dw!!!! I did this practical this week and you won’t acc get a permanent colour change. Basically you have to put the KMNO4 in until the solution goes pink, but upon standing the pink colour WILL fade. This is because the manganate and the iron ions have a reaction that turns the solution colourless again. As soon as you see the solution turn pink, you record your titre. On my practical sheet it did say ‘add potassium manganate until the solution turns pink, and upon standing the pink colour disappears’ so dw about it. The reaction will happen anyways, meaning no matter how much manganate you add, the iron sulfate and potassium manganate solution will eventually revert to colourless. Hope I helped Xx
    I appreciate the reply so much, I've been scratching my head all week trying to figure this out. I did eventually record results just from when I saw a pink colour and I got an average titre of 9.1 cm^3. After calculations that works out to be 25mg of iron per tablet but according to the bottle, its actually 14mg so that's a bummer. Idk whether to stick with it or try again? How was ur experience with this practical? Anything similar?
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    (Original post by Pigster)
    Do you know the approximate percentage of iron in the tablets? Could you look some standard values up? Can you then do the calculations to work out the approximate expected volume of KMnO4 that you should need?

    When you do the practical and you add your calculated estimate and you get a pink colour, like Soveryanonymous says, take that as your endpoint, even if the colour reverts to colourless.

    When you say "no matter how much", what sort of volume are we talking? Have you tried one drop of your iron solution and add dropwise the KMnO4 solution. I'll bet that when the manganate is in large excess it'll be pink/purple.
    I did the calculations and I'm expected to use about 5 cm^3 of potassium permanganate which seems very low. I can use a whole 50cm^3 burette of potassium permanganate but it will still revert back to colourless after a while.
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    (Original post by ahfae)
    I appreciate the reply so much, I've been scratching my head all week trying to figure this out. I did eventually record results just from when I saw a pink colour and I got an average titre of 9.1 cm^3. After calculations that works out to be 25mg of iron per tablet but according to the bottle, its actually 14mg so that's a bummer. Idk whether to stick with it or try again? How was ur experience with this practical? Anything similar?
    Tbh I did struggle with this practical 😅. Both me and my partner in our write-up did actually end up having less iron per tablet than the bottle tho so maybe that’s just how it is? Idk tbh I’m not sure, I’m not that great at chemistry practicals 🤧X
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    (Original post by Soveryanonymous)
    Tbh I did struggle with this practical 😅. Both me and my partner in our write-up did actually end up having less iron per tablet than the bottle tho so maybe that’s just how it is? Idk tbh I’m not sure, I’m not that great at chemistry practicals 🤧X
    hahahahah at least u have less than more, just doesn't make sense to me. Thanks for all ur help anyway tho. Any chance you can send me a copy of ur method sheets? Yours seems better since it told you about the colour fading but if u cant, its all good
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