Madz178
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so i have this question about electrolysis and it is the electrolysis of copper chromate - the question is to explain why there is a colour change at the positive electrode?
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gd99
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What are your current thoughts about what the answer could be? If you can try to explain what you’re thinking/where you’ve got to then I or someone else can either correct you or explain it more efficiently.
Maybe try to start by thinking about what is happening at the electrode in electrolysis?
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Madz178
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(Original post by gd99)
What are your current thoughts about what the answer could be? If you can try to explain what you’re thinking/where you’ve got to then I or someone else can either correct you or explain it more efficiently.
Maybe try to start by thinking about what is happening at the electrode in electrolysis?
so i know that copper is blue and chromate is yellow - chromate is negative so it goes to the positive electrode so the colour change but i don't know how to explain why it is
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gd99
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(Original post by Madz178)
so i know that copper is blue and chromate is yellow - chromate is negative so it goes to the positive electrode so the colour change but i don't know how to explain why it is
That sounds correct so far. You need to think about the oxidation and reduction which takes place at the electrodes. The blue copper in the solution is because of Copper 2+ ions, and the yellow from the Chromate 2- ions, as you have identified. The most likely reason is that the chromate ions are oxidised at the positive electrode (remember OILRIG - oxidation is loss, reduction is gain of electrons). When an ion gains or loses electrons (changes its oxidation state), the colour often changes as well.

As a bonus, although you haven't mentioned it being asked in the question, you could probably expect pure copper metal to be formed at the negative electrode (this is a way of removing impurities from copper).

I don't know whether you need more detail about what the colour changes to, but you may be able to find this in a textbook (I don't know it off the top of my head - it's been a while since I've looked at the GCSE syllabus!).

Finally, if anyone else thinks I've missed anything or that this is not exactly what is needed please do comment and correct it - I'm not a GCSE teacher and it's been a while since I did GCSEs!
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