username3835832
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http://pmt.physicsandmathstutor.com/...Potentials.pdf

Question 6a
Does the half-cell on the right also have a standard hydrogen electrode?
I'm confused, I thought an electrochemical cell may only have one standard hydrogen electrode connected to an other half-cell?
Or is it different here as chlorine is not a metal?

Markscheme:
D = Cl2(g)
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j4mil417
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I’ve just remembered, a carbon rod can be used just like a platinum rod because they both conduct electricity. So that’s why carbon can be used or platinum.

An electrochemical cell can be two half cells together. In order to measure the standard electrode potential of a half cell you have to connect it up to a standard hydrogen electrode in order to measure the EMF value. If you connect two half cells together your measuring the EMF between those two for instance the zinc and copper half cells put together.

The standard hydrogen electrode is always on the left electrode always no matter if the other half cell has a much more negative electrode potential than it. It’s the standard.

Yes and D is chlorine gas because chlorine gas is reduced to chloride ions. Chlorine in its physical state at room temperature exists as a gas. Therefore Chlorine gas is not a metal therefore a platinum electrode has to be used in order to conduct electricity.

Hope that’s helped.
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username3835832
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(Original post by j4mil417)
I’ve just remembered, a carbon rod can be used just like a platinum rod because they both conduct electricity. So that’s why carbon can be used or platinum.

An electrochemical cell can be two half cells together. In order to measure the standard electrode potential of a half cell you have to connect it up to a standard hydrogen electrode in order to measure the EMF value. If you connect two half cells together your measuring the EMF between those two for instance the zinc and copper half cells put together.

The standard hydrogen electrode is always on the left electrode always no matter if the other half cell has a much more negative electrode potential than it. It’s the standard.

Yes and D is chlorine gas because chlorine gas is reduced to chloride ions. Chlorine in its physical state at room temperature exists as a gas. Therefore Chlorine gas is not a metal therefore a platinum electrode has to be used in order to conduct electricity.

Hope that’s helped.
Is platinum electrode used for non metals e.g. a gas? (I know it can also be used if there's a solution of two aquaous ions of the same metal)
Also, in the picture of question 6, the does D (half-cell on the right) have a similar shape to the standard hydrogen electrode on the left? Is it because it is a non metal (a gas)

Also
for question 6c is ClO3- a non-metal?
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j4mil417
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So a platinum electrode is always used when no metal is present so in aqueous solutions and anything with gas. A solid electrode is required which conducts electricity.

The shape of the electrode doesn’t matter. When drawing the diagram you just want everything to be almost the same. The shape doesn’t contribute anything to the EMF value or anything. You must label everything correctly if they ask so.

For question 6c, ClO3- is part of chloric acid which is an aqueous solution it isn’t a solid nor a metal. Therefore a solid platinum electrode will need to be used to conduct electricity.
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(Original post by j4mil417)
So a platinum electrode is always used when no metal is present so in aqueous solutions and anything with gas. A solid electrode is required which conducts electricity.

The shape of the electrode doesn’t matter. When drawing the diagram you just want everything to be almost the same. The shape doesn’t contribute anything to the EMF value or anything. You must label everything correctly if they ask so.

For question 6c, ClO3- is part of chloric acid which is an aqueous solution it isn’t a solid nor a metal. Therefore a solid platinum electrode will need to be used to conduct electricity.
for question 6bi, do electrons always flow from the standard hydrogen electrode to the other half-cell?

Also are platinum, carbon and graphite all 3 solid electrodes that can conduct electricity and are inert? And they are used in aqeous solutions (eg. fe2+ and fe3+) in a half cell and when there's a gas?

Also question 7c.
I understand the question but just wondering, even though chlorine and iodine are gases they can reduce/oxidise a metal and therefore it all depends on the electrode potentials?
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j4mil417
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Have you done electrochemical cells topic in class yet?

If using the standard hydrogen electrode electrons always flow from the standard hydrogen electrode to the other half cell. So the standard hydrogen electrode is oxidised while the other half cell is reduced.

They can all be used as an electrode in the solid state because they are inert and conduct electricity to allow the flow of electrons. These electrodes are only used when no other solid metal is present. So there used in aq solutions including gas.
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(Original post by chemquestion)
for question 6bi, do electrons always flow from the standard hydrogen electrode to the other half-cell?

Also are platinum, carbon and graphite all 3 solid electrodes that can conduct electricity and are inert? And they are used in aqeous solutions (eg. fe2+ and fe3+) in a half cell and when there's a gas?

Also question 7c.
I understand the question but just wondering, even though chlorine and iodine are gases they can reduce/oxidise a metal and therefore it all depends on the electrode potentials?
The gases can oxidise and reduce a metal but yes it all depends on electrode potentials. The most negative is oxidised and the most positive is reduced.
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