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Chemistry P4| A2 only

DragonCub

DragonCub

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musa Khan said:
guys, can you confirm whether I've got my facts right? okay so in the electrochemical cell, the electrode at the left hand side is essentially a cathode and the equation which involves a more negative electrode potential value goes here but instead of reduction oxidation takes place here and the electrons are released while on the right hand side we have an anode and recuction takes place here and the more positive electrode potential value comes here (less reactive equation) and the electrons are used up?
Click to expand...
Well, be careful here: where E(red) is MORE NEGATIVE is the ANODE. The anode always has the oxidation reaction taking place and that's why it is called the anode. Surely in the cell electron flows from it to the other electrode so that it is the negative electrode, but it is still the anode, just because oxidation happens on it.
Vice-versa, the cathode is where reduction takes place.

And one more point: the relative positions don't matter. Like in a copper-zinc cell, if you exchange the positions of the Cu/Cu(2+) cell and the Zn/Zn(2+) cell, electron flow direction is not affected (still from Zn to Cu), nor is the E(cell) and the reactions taking place.
 
DragonCub

DragonCub

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sahania said:
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_41.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_ms_41.pdf
please tell me how to solve Q2(a) iv
Click to expand...
As in (i) you get the orders all 1. So the formula is rate = k[CH3CHO][CH3OH][H+]
According to number 1 experiment, k × 0.20 × 0.10 × 0.05 = 1.00, k × 0.001 = 1.00, k = 1000
then when all concentrations are 0.20,
rate = 1000 × 0.20 × 0.20 × 0.20 = 8.00
 
M

musa Khan

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DragonCub said:
Well, be careful here: where E(red) is MORE NEGATIVE is the ANODE. The anode always has the oxidation reaction taking place and that's why it is called the anode. Surely in the cell electron flows from it to the other electrode so that it is the negative electrode, but it is still the anode, just because oxidation happens on it.
Vice-versa, the cathode is where reduction takes place.

And one more point: the relative positions don't matter. Like in a copper-zinc cell, if you exchange the positions of the Cu/Cu(2+) cell and the Zn/Zn(2+) cell, electron flow direction is not affected (still from Zn to Cu), nor is the E(cell) and the reactions taking place.
Click to expand...


But isn't the oxidation and reduction rule reversed for electrochemical cells? i.e oxidation at CATHODE and reduction at ANODE? this is so confusing :/so you're basically saying that I've got all my facts wrong? and the more negative reduction potential value occurs at the anode? please explain it in more detail with some example perhaps?


http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_43.pdf

look at this paper, in question number eight , the equation with the more positive value is associated with the 'positive' electrode meaning anode basically, right? or is the anode the negative electrode? :/ ? or is some other logic being applied here?

and also what direction do electrons travel from? anode to cathode? is that saying from the more negative potential to the more positive one?

okay,so I researched this a bit and I think I mixed up my electrochemical cell and electrolytic cell so is the car battery an example of an electrolytic cell?


I still don't get it :/ someone please explain it to me, just tell me all the things I need to remember here including how to identify the anode and cathode using electrode potentials and the direction of the flow of charge and where these two electrodes usually go (which one's on left, which one's on right?) and their relative charges (which one is positive and which one is negative)
 
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musa Khan

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DragonCub See my post above then read this, okay so I tried to explain this to myself and came up with this :p if we take thee zn and mg reaction then mg having a more negative value of electrode potential will undergo oxidation and vice versa for Zn, does this mean that zinc occurs at the cathode and Mg at anode since Mg is being oxidized and Zn reduced? so essentially the more negative reduction potential value occurs at the anode? but what was up with the question I posted above in the question paper? doesn't fit in with this explanation and also, do the electrons flow from anode to cathode? but isn't anode always positive? you said it's negative? :/
 
princesskt

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musa Khan said:
DragonCub See my post above then read this, okay so I tried to explain this to myself and came up with this :p if we take thee zn and mg reaction then mg having a more negative value of electrode potential will undergo oxidation and vice versa for Zn, does this mean that zinc occurs at the cathode and Mg at anode since Mg is being oxidized and Zn reduced? so essentially the more negative reduction potential value occurs at the anode? but what was up with the question I posted above in the question paper? doesn't fit in with this explanation and also, do the electrons flow from anode to cathode? but isn't anode always positive? you said it's negative? :/
Click to expand...
anode can be negative as well see anode undergoes oxidation it means electron are lost it also means the here electrons are more in number so it is negative................
hope it makes clear............in some ques cie has reversed anode cathode i think just to confuse...................................................................
 
DragonCub

DragonCub

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musa Khan said:
But isn't the oxidation and reduction rule reversed for electrochemical cells? i.e oxidation at CATHODE and reduction at ANODE? this is so confusing :/so you're basically saying that I've got all my facts wrong? and the more negative reduction potential value occurs at the anode? please explain it in more detail with some example perhaps?


http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_43.pdf

look at this paper, in question number eight , the equation with the more positive value is associated with the 'positive' electrode meaning anode basically, right? or is the anode the negative electrode? :/ ? or is some other logic being applied here?

and also what direction do electrons travel from? anode to cathode? is that saying from the more negative potential to the more positive one?

okay,so I researched this a bit and I think I mixed up my electrochemical cell and electrolytic cell so is the car battery an example of an electrolytic cell?


I still don't get it :/ someone please explain it to me, just tell me all the things I need to remember here including how to identify the anode and cathode using electrode potentials and the direction of the flow of charge and where these two electrodes usually go (which one's on left, which one's on right?) and their relative charges (which one is positive and which one is negative)
Click to expand...
musa Khan said:
DragonCub See my post above then read this, okay so I tried to explain this to myself and came up with this :p if we take thee zn and mg reaction then mg having a more negative value of electrode potential will undergo oxidation and vice versa for Zn, does this mean that zinc occurs at the cathode and Mg at anode since Mg is being oxidized and Zn reduced? so essentially the more negative reduction potential value occurs at the anode? but what was up with the question I posted above in the question paper? doesn't fit in with this explanation and also, do the electrons flow from anode to cathode? but isn't anode always positive? you said it's negative? :/
Click to expand...
Okay here's the point:
Anode is NOT defined as the positive electrode.
Instead, it is the electrode where OXIDATION takes place.
In the Zn-Mg cell you mentioned, yes because Mg has a more negative E(red) it gets oxidised so the Mg electrode is the anode.
Think it this way: the electrode potential represents how willing an element is to be reduced. The more negative it is, the less willing the element is to reduction. In other words, the more negative means the element is more willing to be oxidised and it has a greater ability to reduce something.
Mg has a more negative E, so it is more likely to be oxidised than Zn. When we connect them together, we will get Zn reduced, and Mg oxidised. So Mg becomes the anode and Zn the cathode.
Next, oxidation is donating out electrons, so Mg gives out electron; Zn reduced, it receives electrons. That's why the electrons flow from Mg, though the wire, to Zn.
Here electrons start from Mg and finish at Zn. Therefore Mg is the negative electrode and Zn the positive.
Mg is the anode and the negative electrode, and Zn is the cathode and the positive electrode.
 
DragonCub

DragonCub

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musa Khan said:
okay,so I researched this a bit and I think I mixed up my electrochemical cell and electrolytic cell so is the car battery an example of an electrolytic cell?
Click to expand...
Electrolytic cell is the other way around.
The positive electrode attracts negative ions, or anions. Since the positive electrode loves electrons, it can "grab" electrons from anions. Once the anions lose electrons they get oxidised. So the positive electrode is the anode.
The negative electrode, similarly, attracts and gives electrons to positive ions, or cations. The cations receive electrons and so get reduced. The negative electrode is the cathode.
 
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ying27kia

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somebody help.
how to draw skeletal formula of amide and carboxylic acid.
do we need to expand N---H bond in skeletal formula?
 
S

shamil

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Reaction kinetics:
are these the only equations:?

Rate= k x conc.

rate = change in conc./ change in time

????? or is there anything im missing cuz it feels like it when i answer the papers and the MS don't really help me out much with this either. Thank you
 
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