Direction of ions in electrolyte

[jasonn93]

In 2 half-cells, it's always cations from the salt bridge going to the cathode, and anions to the anode right ?
How about in something like a lead-acid accumulator? I followed the logic above and concluded that the H+ ions would be migrating toward the cathode? But in STAV 09 they say it's the SO4 2- ions?
Q. Which ions in the electrolyte of the battery would have a net migration towards the
positive electrode?
A. The negatively charged SO4 2- (aq) (1 mark)

Thanks

[scocliffe09]

I think you're right.
Do you mean STAV 2009 Q6c? because my answers say "the positively charged H+ (aq)" which is right...

[stonecold]

I think you're right.
Do you mean STAV 2009 Q6c? because my answers say "the positively charged H+ (aq)" which is right...

Nah, this question dicked everyone.

You have to work out which cell is getting more positive and which is getting more negative, then distribute charges as required.  There is no set rule as such...

[jasonn93]

Hmm so are you saying that since at the cathode, electrons are getting used up, therefore it becomes more positive at the cathode, so the anion has to move to the cathode to compensate?

[scocliffe09]

I think you're overcomplicating a simple question.

Q. Which ions in the electrolyte of the battery would have a net migration towards the positive electrode?

positive electrode in galvanic cell = cathode = reduction
--> electrons are migrating towards the cathode to enable PbO2 molecules to undergo reduction.
To balance the charge, cations flow the same way as electrons, hence H+ ions migrate towards the positive electrode.

I can't really see what's particularly difficult about this question compared to any other galvanic cells question...

[stonecold]

I think you're overcomplicating a simple question.

Q. Which ions in the electrolyte of the battery would have a net migration towards the positive electrode?

positive electrode in galvanic cell = cathode = reduction
--> electrons are migrating towards the cathode to enable PbO2 molecules to undergo reduction.
To balance the charge, cations flow the same way as electrons, hence H+ ions migrate towards the positive electrode.

I can't really see what's particularly difficult about this question compared to any other galvanic cells question...

I did this like a month ago and for some reason it is different...

[kyzoo]

You can also work it out like this: In order for a complete circuit to be established, a circular path of negative charges must be establishes. So if the electrons go from left-to-right, then the negative ions must go from right-to-left in order to create a circular circuit of negative charges.

[jasonn93]

Hmm..makes sense, kinda thanks all! I'll have to look this stuff up more..the circular path of -ve charges sounds interesting haha ! on a separate note, for question 9d could you say that the iron electrode would produce a spontaneous reaction with F2 (g) therefore a carbon one needs to be used? They say that it is because 'Iron is a stronger reductant than the fluoride ion and would be oxidised in preference.' but is there an alternate answer? Thanks again

[stonecold]

Hmm..makes sense, kinda thanks all! I'll have to look this stuff up more..the circular path of -ve charges sounds interesting haha ! on a separate note, for question 9d could you say that the iron electrode would produce a spontaneous reaction with F2 (g) therefore a carbon one needs to be used? They say that it is because 'Iron is a stronger reductant than the fluoride ion and would be oxidised in preference.' but is there an alternate answer? Thanks again

Nah, with electrolysis, you always assume the reactants and products are kept separate so no reaction between them occurs.

[jasonn93]

Oooh fair enough! thanks