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    Hi,

    I'm slightly confused about the colour changes that occur with potassium manganate...

    As far as I'm aware, when it is added to something that can be oxidised, it goes purple --> colourless..
    However, sometimes a brown solution is formed?? What causes this to happen?

    Thanks
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    (Original post by Sarah182)
    Hi,

    I'm slightly confused about the colour changes that occur with potassium manganate...

    As far as I'm aware, when it is added to something that can be oxidised, it goes purple --> colourless..
    However, sometimes a brown solution is formed?? What causes this to happen?

    Thanks
    Manganate is an intense purple colour which goes colourless, the brown solution is caused when you forget to acidify with sulphuric acid :P
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    (Original post by Sarah182)
    Hi,

    I'm slightly confused about the colour changes that occur with potassium manganate...

    As far as I'm aware, when it is added to something that can be oxidised, it goes purple --> colourless..
    However, sometimes a brown solution is formed?? What causes this to happen?

    Thanks
    The brown colour is partial reduction to Mn(IV). This may happen in alkaline or neutral medium, or simply because the reductant is not strong enough to take the reaction any further.
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    ahh, thankyou!

    Brown = partial reduction, okay!
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    Alkenes react with potassium manganate(VII) solution in the cold. The colour change depends on whether the potassium manganate(VII) is used under acidic or alkaline conditions.

    If the potassium manganate(VII) solution is acidified with dilute sulphuric acid, the purple solution becomes colourless.

    If the potassium manganate(VII) solution is made slightly alkaline (often by adding sodium carbonate solution), the purple solution first becomes dark green and then produces a dark brown precipitate.
    http://www.chemguide.co.uk/organicpr...nes/kmno4.html
 
 
 
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