Eo Gchem HARD

[silveryhair]

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A What is the theoretical voltage required to electrolyze molten NaCl that forms Cl2(g) at anode and Na(l) at cathode, given Eo for Na+/Na is –2.71 V and Eo for Cl2/Cl- is +1.36 V?
A. 0.00 V B. 1.35 V C. 1.36 V D. 2.71 V E. 4.07 V

 

[ucla2134]

A What is the theoretical voltage required to electrolyze molten NaCl that forms Cl2(g) at anode and Na(l) at cathode, given Eo for Na+/Na is –2.71 V and Eo for Cl2/Cl- is +1.36 V?
A. 0.00 V B. 1.35 V C. 1.36 V D. 2.71 V E. 4.07 V

I think the answer is E but it should be -4.07, strange

 

[doc3232]

I think the answer is E but it should be -4.07, strange

-4.07 would be the reverse nonspontaneous reaction. The spontaneous reaction will always be positive.

 

[ldm0208]

EMP=1.36v+2.71v=4.07v is E the answer? yes no?

 

[doc3232]

EMP=1.36v+2.71v=4.07v is E the answer? yes no?

The way the OP write it is awkward, we need it to be in the form of a reaction to see whether the voltage is neg or pos.

 

[silveryhair]

yes it is 4.07. But why? when they dont show the equation, i dont get how to do it. Can someone explain? Thanks!

 

[PooyaH]

yes it is 4.07. But why? when they dont show the equation, i dont get how to do it. Can someone explain? Thanks!

NaCl -> Na+ + Cl-

Na+ -> Na = -2.71 V

Cl -> Cl- = +1.36 V

Since Na is being oxidized E should be +2.71 V, thus,

2.71 + 1.36 = 4.07 V

 

[ldm0208]

NaCl -> Na+ + Cl-

Na+ -> Na = -2.71 V

Cl -> Cl- = +1.36 V

Since Na is being oxidized E should be +2.71 V, thus,

2.71 + 1.36 = 4.07 V

below is how I did same as pooyah. But I came up with a question!
Na(+) + e(-) -> Na Eo= -2.71v
Cl2 + 2e(-) -> 2Cl(-) Eo= +1.36v

Cl2 gets reduced, so we keep it as it is.
Na gets oxidized, so we reverse the sign.
And jus add them up.

The problem says "molten NaCl that forms Cl2(g) at anode and Na(l) at cathode"
So, my question is if Cl2 is formed at ANODE, should it get oxidized? also for Na, it's formed at CATHODE, so should be reduced?

 

[ucla2134]

NaCl -> Na+ + Cl-

Na+ -> Na = -2.71 V

Cl -> Cl- = +1.36 V

Since Na is being oxidized E should be +2.71 V, thus,

2.71 + 1.36 = 4.07 V

hey but i think the CL is oxidized and Na is reduced since the title says that it forms CL2 (gas) at the anode. So my equation is -2.71-1.35=-4.07, which is nonspontaneous in the direction written, and spontaneous in the reverse direction. Can somebody tells me if i am right or not? Thanks

 

[silveryhair]

below is how I did same as pooyah. But I came up with a question!
Na(+) + e(-) -> Na Eo= -2.71v
Cl2 + 2e(-) -> 2Cl(-) Eo= +1.36v

Cl2 gets reduced, so we keep it as it is.
Na gets oxidized, so we reverse the sign.
And jus add them up.

The problem says "molten NaCl that forms Cl2(g) at anode and Na(l) at cathode"
So, my question is if Cl2 is formed at ANODE, should it get oxidized? also for Na, it's formed at CATHODE, so should be reduced?

Thats what i was thinking, and I ended up with C and its wrong.

 

[ldm0208]

Thats what i was thinking, and I ended up with C and its wrong.

My answer is E not C.

hey but i think the CL is oxidized and Na is reduced since the title says that it forms CL2 (gas) at the anode. So my equation is -2.71-1.35=-4.07, which is nonspontaneous in the direction written, and spontaneous in the reverse direction. Can somebody tells me if i am right or not? Thanks

Exactly, that was my concern about this question.
But now I am thinking the answer is -4.07 if they asked emf?
They are just asking the theoretical voltage required? so we just ignore the sign???

 

[silveryhair]

NaCl -> Na+ + Cl-

Na+ -> Na = -2.71 V

Cl -> Cl- = +1.36 V

Since Na is being oxidized E should be +2.71 V, thus,

2.71 + 1.36 = 4.07 V

How do we know that Na is oxidized?

 

[yakuza]

This problem is definitely wrong..
Eo= -4.07 v

Its an electrolytic cell so its NONspontaneous bc therefore Eo= negative
Electrolysis can not be positive

Cl- --> Cl2(g) oxidation
Cl2 gas is being formed since Cl- is forced to be oxidized

Na+ --> Na(l) reduction
Na liquid is formed since Na+ is forced to be reduced

 

[PooyaH]

How do we know that Na is oxidized?

This is an example of electrolysis. since it says we get Cl2 at anode it means it's being reduced and Na at cathode means Na is being oxidized. Remember, in electrolysis we're forcing a non-spontaneous reaction to happen unlike in a galvanic cell (like a battery). In electrolysis electrons the electrons still go from the anode to the cathode but at the anode they get reduced instead of oxidized! However, I think it should give a negative number since we're forcing a non-spontaneous reaction to be spontaneous!

 

[joonkimdds]

A What is the theoretical voltage required to electrolyze molten NaCl that forms Cl2(g) at anode and Na(l) at cathode, given Eo for Na+/Na is –2.71 V and Eo for Cl2/Cl- is +1.36 V?
A. 0.00 V B. 1.35 V C. 1.36 V D. 2.71 V E. 4.07 V

How can NaCl form 1 Na and 2 Cl???

 

[ldm0208]

This is an example of electrolysis. since it says we get Cl2 at anode it means it's being reduced and Na at cathode means Na is being oxidized. Remember, in electrolysis we're forcing a non-spontaneous reaction to happen unlike in a galvanic cell (like a battery). In electrolysis electrons the electrons still go from the anode to the cathode but at the anode they get reduced instead of oxidized! However, I think it should give a negative number since we're forcing a non-spontaneous reaction to be spontaneous!

you got the concept mixed!
From KAP REVIEW
"in an electrolytic cell, the anode is + and the cathode is -, but in a galvanic cell it's opposte. HOWEVER, in both types of cells, reduction occurs at the cathode and oxidation occurs at the anode"

 

[yakuza]

In electrolysis you pretty much always use a molten solution, and the 2 sticks in them are Na+ and Cl-. You start with Cl- + Na+ ----> Na metal and Cl gas

And in galvanic and electrolysis, its ALWAYS going from Anode--->Cathode

BUT in electrolysis, the + is on the anode and - is on the cathode, SO the whole electrons are being forced like this: + ---electrons---> -

I think the way the op wrote the Eo is wrong

 

[ldm0208]

In electrolysis you pretty much always use a molten solution, and the 2 sticks in them are Na+ and Cl-. You start with Cl- + Na+ ----> Na metal and Cl gas

And in galvanic and electrolysis, its ALWAYS going from Anode--->Cathode

BUT in electrolysis, the + is on the anode and - is on the cathode, SO the whole electrons are being forced like this: + ---electrons---> -

I think the way the op wrote the Eo is wrong

you got it! I agree!
one question I came up for you why the answer here is not neg.

I am thinking the answer is -4.07 if they asked emf?
But, they are just asking the theoretical voltage required? so we just ignore the sign??? Stupid question??

 

[yakuza]

you got it! I agree!
one question I came up for you why the answer here is not neg.

I am thinking the answer is -4.07 if they asked emf?
But, they are just asking the theoretical voltage required? so we just ignore the sign??? Stupid question??

voltage, EMF, cell potential are the same thing. Theoretical will be the maximum

 

[ldm0208]

voltage, EMF, cell potential are the same thing. Theoretical will be the maximum

well..then like you said earlier I guess there is no answer to choose from the choices..

 

[joonkimdds]

I got +4.07. (and don't know why ppl think it's minus)