Who's right STAV or me???

[ggxoxo]

I was doing this question: I'll briefly summarise it-

In a lead-acid accumulator, which ions in the electrolyte (H2SO4) would have a net migration towards the positive electrode?

I said H+

but STAV said SO42-

I don't get it because in a galvanic cell (as this battery), doesn't the positive ion go to teh positive electrode???

[thushan]

I was doing this question: I'll briefly summarise it-

In a lead-acid accumulator, which ions in the electrolyte (H2SO4) would have a net migration towards the positive electrode?

I said H+

but STAV said SO42-

I don't get it because in a galvanic cell (as this battery), doesn't the positive ion go to teh positive electrode???

That's a little vague - is the cell being discharged or recharged?

[ggxoxo]

discharged

[thushan]

OK let's think...discharge - so through the wire the electrons travel from - to +, meaning through the solution the anions travel from + to -.

Hold on...you're right.

[sam0001]

I don't agree. If you're producing a positive charge, to maintain electro neutrality, wouldn't the negative ions migrate towrards the pb2+ ions?

[thushan]

I don't agree. If you're producing a positive charge, to maintain electro neutrality, wouldn't the negative ions migrate towrards the pb2+ ions?

The electrode polarity doesn't necessarily mean the charge of the electrode per se. It simply means the force of the cell itself (in the absence of an external power source) on the electrons - so the electrons have a natural tendency in the wire to move towards the positive electrode (assuming no external power source).

[sam0001]

Yeah I get that, but if you're producing positive charge, there would be a build of charge. To negate this effect, wouldn't the negative ions drift towards the positive ions to counteract the charge?

....im confused

[Hancock]

Little trick I used: Anions go to anode. Cations go to cathode.

[thushan]

Yeah I get that, but if you're producing positive charge, there would be a build of charge. To negate this effect, wouldn't the negative ions drift towards the positive ions to counteract the charge?

....im confused

Actually, you're LOSING positive charge at the cathode here. PbO2 is being reduced to PbSO4. In effect, it's really a conversion of Pb4+ to Pb2+ if you want to look at it that way. Yes, you're producing a positively charged species (Pb2+) but it was produced from an even more positively charged species ('Pb4+'). So you're losing positive charge. So you'd want cations to replace that lost charge.