A2 Electrochemical Cells: Why is Pt sometimes put in when the cell is drawn?

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i'mlaura
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For example, in fuel cells the cell is drawn as:

Pt | H2(g) | OH–(aq) ,H2O (l) || O2 (g) | H2O(l) ,OH–(aq) | Pt

Also, are the commas used because the two molecules are both oxidised?
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charco
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(Original post by i'mlaura)
For example, in fuel cells the cell is drawn as:

Pt | H2(g) | OH–(aq) ,H2O (l) || O2 (g) | H2O(l) ,OH–(aq) | Pt

Also, are the commas used because the two molecules are both oxidised?
Pt is put in because it is there!

The comma separates two substances in the same phase.
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i'mlaura
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(Original post by charco)
Pt is put in because it is there!

The comma separates two substances in the same phase.
So is Pt always there? If one was oxidised and one was reduced but they were both in the same phase, would they still go like that in the middle?

Thanks

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charco
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(Original post by i'mlaura)
So is Pt always there? If one was oxidised and one was reduced but they were both in the same phase, would they still go like that in the middle?

Thanks

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No, some electrochemical cells do not have platinum electrodes. Pt is only used when a catalytic surface is needed ...

I'm not sure what you are asking in your second question.
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i'mlaura
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(Original post by charco)
No, some electrochemical cells do not have platinum electrodes. Pt is only used when a catalytic surface is needed ...

I'm not sure what you are asking in your second question.
Thank you, is a catalytic surface needed with rechargeable and non-rechargeable batteries?

When I've learnt about the cell diagrams before (I showed one in my original post), it was reduction on the outside and oxidised molecules in the middle. So if there are three molecules on the left and two are separated by a comma in the middle, does that mean they are in the same state and were both oxidised?
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charco
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(Original post by i'mlaura)
Thank you, is a catalytic surface needed with rechargeable and non-rechargeable batteries?

When I've learnt about the cell diagrams before (I showed one in my original post), it was reduction on the outside and oxidised molecules in the middle. So if there are three molecules on the left and two are separated by a comma in the middle, does that mean they are in the same state and were both oxidised?
A catalytic surface is needed to allow two species that would not normally react to come into contact and react. It depends on the design of both the rechargeable and non-rechargeable battery.

You would need to provide examples of what you mean ...
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i'mlaura
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Pt | H2(g) | OH–(aq) ,H2O (l) || O2 (g) | H2O(l) ,OH–(aq) | Pt

On the left, are OH- and H2O both oxidised, you also said that a comma means they are in the same state, but here they aren't.

A zinc- carbon non- rechargeable battery? How would I know when to add in the platinum electrode? Would it say in the question?
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charco
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(Original post by i'mlaura)
Pt | H2(g) | OH–(aq) ,H2O (l) || O2 (g) | H2O(l) ,OH–(aq) | Pt

On the left, are OH- and H2O both oxidised, you also said that a comma means they are in the same state, but here they aren't.

A zinc- carbon non- rechargeable battery? How would I know when to add in the platinum electrode? Would it say in the question?
No, I said that they are both in the same phase. They are both in aqueous phase.

On the LHS the hydrogen is oxidised. On the RHS the oxygen is reduced

Zinc-carbon batteries do not need a catalytic surface.
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i'mlaura
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(Original post by charco)
No, I said that they are both in the same phase. They are both in aqueous phase.

On the LHS the hydrogen is oxidised. On the RHS the oxygen is reduced

Zinc-carbon batteries do not need a catalytic surface.
Oh right okay thanks.

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bakergirl
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Pt is needed as you need somewhere the attach the croc clip (so you can measure voltage). So is used when gases/aqueous/liquid with no solid. It is used as it inert and conducts electricity.
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