Please Help: Multiple Choice Question (1 Viewer)

[Equilibrium1]

A student measures the voltage between pairs of metal strips when placed in sodium sulfate solution.

Which metals gives the highest positive voltage in combination with copper?

a) Silver
b) Tin
c) Zinc
d) Magnesium

The answer is A (silver) but I don't know why =/

Thank you!

 

[someth1ng]

This is a very weird question...I don't even know why there's even redox occuring...

Sodium is pretty much the most reactive and will stay in solution, how can there be reduction or oxidation for any emf to be produced?

 

[golgo13]

Ok i think the explanation is that when you put a metal into another metal solution like so that also begins to compete with the metal electrodes. In which case like someth1ng said is the sodium solution. Also note the question asks for positive and in this case it leaves silver and tin and silver has the larger value

Just out of curiosity where did u pull this question from? I'm slight doubts about the provided solution

 

[Equilibrium1]

Ok i think the explanation is that when you put a metal into another metal solution like so that also begins to compete with the metal electrodes. In which case like someth1ng said is the sodium solution. Also note the question asks for positive and in this case it leaves silver and tin and silver has the larger value

Just out of curiosity where did u pull this question from? I'm slight doubts about the provided solution

The question is from the Independent chemistry paper 2007 (Q3 I believe...)

 

[someth1ng]

Personally, I don't see how there would be any emf produced between the metal electrodes. Because the Na+ ions will not be able to be reduced and so, none of the electrons will be oxidised, hence, no emf produced.

This is what confuses me - I don't see how an emf can possibly be made. Not only that, but when it says "highest positive voltage", does it mean just magnitude because positive/negative will depend on which electrodes are connected terminal of the voltmeter.

 

[barbernator]

my mind is quite frazzled.

 

[Riproot]

Wouldn't the copper go to Cu2+ and then go over and plant it's fine ass on Ag and then form Cu(s)?

 

[barbernator]

Wouldn't the copper go to Cu2+ and then go over and plant it's fine ass on Ag and then form Cu(s)?

but what i'm unsure about is why copper would reduce the sodium ions in the first place, because it is less reactive than sodium...

 

[Riproot]

It wouldn't… wouldn't they just float around together?
There's room for more fun!
It's like a threesome but chemistry style instead of a devil's three way.

 

[barbernator]

It wouldn't… wouldn't they just float around together?
There's room for more fun!
It's like a threesome but chemistry style instead of a devil's three way.

csb. how do the copper ions get into solution in the first place then? the question says that there are only sodium ions in solution and the copper electrons have to go somewhere for it to get into solution.

 

[Riproot]

csb. how do the copper ions get into solution in the first place then? the question says that there are only sodium ions in solution and the copper electrons have to go somewhere for it to get into solution.

tbh, I was just making shit up, but it totes makes sense, like, the Na can form NaOH and then give off H+ and then the acid would break down the metal.

Na⁺_(aq) H₂O_(l) <---> NaOH_(aq) + H⁺_(aq)

 

[barbernator]

nvm. H+ cannot be reduced to H2(g) by either Ag or Cu.

 

[Riproot]

So…?

 

[someth1ng]

The question is broken...at least everyone seems to have the same idea I did - now I can be assured that there's no hole in my knowledge.

 

[mathfreak94]

This is a tricky question and im convinced that the answer provided is incorrect. The trick here is the "sodium sulphate solution".
i.e it is a galvanic cell with copper as an electrode and another metal as the other electrode (the unknown) with an electrolyte containing Na+, SO4- AND H2O. In each of the options provided (Ag,Sn,Zn and Mg) only the couple Cu/Ag will have the copper be oxidised as it is more reactive (refer to redox table) and therefore the H2O in the solution will get reduced as it is a better electron acceptor than the Ag and Na+ (Note: the Na+ does not get reduced in any situation as H2O is more positive). As E cell = E oxid + E red the total voltage produced in this case is -1.17V. In the other options, The Sn, Zn and Mg will be oxidised instead of the copper as it is more reactive, and again the H2O in solution will be reduced. By adding the cell potentials again the most positive one will be Mg (+1.53V)

So basically i disagree with the answer Hope this helps

 

[someth1ng]

This is a tricky question and im convinced that the answer provided is incorrect. The trick here is the "sodium sulphate solution".
i.e it is a galvanic cell with copper as an electrode and another metal as the other electrode (the unknown) with an electrolyte containing Na+, SO4- AND H2O. In each of the options provided (Ag,Sn,Zn and Mg) only the couple Cu/Ag will have the copper be oxidised as it is more reactive (refer to redox table) and therefore the H2O in the solution will get reduced as it is a better electron acceptor than the Ag and Na+ (Note: the Na+ does not get reduced in any situation as H2O is more positive). As E cell = E oxid + E red the total voltage produced in this case is -1.17V. In the other options, The Sn, Zn and Mg will be oxidised instead of the copper as it is more reactive, and again the H2O in solution will be reduced. By adding the cell potentials again the most positive one will be Mg (+1.53V)

So basically i disagree with the answer Hope this helps

...but you can't oxidise copper in this setup...

 

[mathfreak94]

...but you can't oxidise copper in this setup...

As i said the copper only gets oxidised with Ag as the other electrode, i.e copper is the anode and silver is the cathode. The reason copper will be oxidised in the setup with Ag, is that it has a more positive oxidation potential than silver. When a more reactive metal is used instead of Ag, (eg Mg) then the Mg will be oxidised at the anode and the copper will act as an inert electrode (does not get reduced as there are no copper ions!) instead in this situation, either the Na+ or H2O will be reduced, so the more positive will be reduced ( that is H2O)