electroplating

[khalil]

What is the purpose of the electrolyte in electroplating?
Why is the cathode negative and the anode positive?
What does the power supply do?

Thanks

[Ilovemathsmeth]

The polarities of the electrodes is imposed by the power supply in electrolysis.

That is, the power supply forcefully withdraws electrons from the ANODE, therefore it is 'positively charged' as there is a loss of electrons and an accumulation of cations around it.

For the cathode, electrons are forced onto it, giving it a negative charge as it is being bombarded with electrons.

In galvanic, it is the reverse because it is the chemical reaction that determines the polarity of the electrode. Oxidation means loss of electrons, i.e., anode is negative here. Reduction means gain of electrons, i.e. the cathode consumes the electrons so is positively charged.

The electrolyte is there to provide a source of ions to migrate to the anode/cathode to prevent build up of charge around the electrodes.

Hope that helps

[khalil]

When recharging a lead-acid cell, why is the positice terminal of the recharger connected to the positice terminal of the cell?

[tripz]

Thanks Ilovemathsmeth =P

@Khalil: I don't know the exact answer, but seeing as we're trying to turn products back to the reactants in order to 'recharge' the lead-acid battery, we're putting a electric charge to make the products turn back into reactants so the battery can be used again just like a rechargeable battery. I really hope I am not wrong...but I'm sure I'm not completely right somehow...

[khalil]

If a question asks to find the products formed at the anode for an electrolysis cell that contains a solution of aqeous chromium(|||) bromide, how will we know where the chromium is located in the elctrochemical series.

[Mao]

Oxidation occurs at the anode in electrolysis, so it'll be the anion that reacts, not the cation.