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ocr a f325 revision thread

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Reply 660
Avatar for Tobeadoc
Tobeadoc
Original post by otrivine
Hi :smile: my friend I did the notes, hope you find them useful


Calculate the pH of 0.40 moldm^-3 Ca(OH2)?? How do you know the concentration of OH-?
Original post by Tobeadoc
Calculate the pH of 0.40 moldm^-3 Ca(OH2)?? How do you know the concentration of OH-?


Ok so what you do is this

Ca(OH)2 ----> Ca2+ + 2OH-

So the concentration of Ca(OH)2 IS 0.40 MOL dm-3

you can see the mole ratio is 1:2 , Ca(OH)2 : 2OH-

SO you can get the concentration of OH- by multiplying by 2 to give you the concentration of OH-. so 0.40 x 2= 0.80

From here you can use the Kw formula to get concentration of H+ and then use the -log(H+) to get the PH.

hope this helped
Reply 662
Avatar for Tobeadoc
Tobeadoc
Original post by otrivine
Ok so what you do is this

Ca(OH)2 ----> Ca2+ + 2OH-

So the concentration of Ca(OH)2 IS 0.40 MOL dm-3

you can see the mole ratio is 1:2 , Ca(OH)2 : 2OH-

SO you can get the concentration of OH- by multiplying by 2 to give you the concentration of OH-. so 0.40 x 2= 0.80

From here you can use the Kw formula to get concentration of H+ and then use the -log(H+) to get the PH.

hope this helped

Thanks so much
Original post by Tobeadoc
Thanks so much


No worries anything else , do tell me :smile:
Reply 664
Avatar for zef1995
zef1995
10
Original post by otrivine
Enjoy, these are the notes I made for electrode potentials including stretch and challenge questions I made on my own and possible questions that could crop up. Anything or if you are not sure about something please inform me and ill try my best to answer any queries :smile:


Hello, thank you for the notes, I'm finding them very helpful! I appreciate you doing that :smile:
I was just wondering if I could ask you a quick question? I'm confusing myself over the anode and cathode in electrochemical cells. I understand that electrons are 'produced' at the most negative half cell, and then these travel to the more positive half cell where they are then 'used', but I don't understand which electrode is which. For example, in a zinc-copper half cell, which electrode is the anode and which electrode is the cathode?
Thank you very much :smile:
Original post by zef1995
Hello, thank you for the notes, I'm finding them very helpful! I appreciate you doing that :smile:
I was just wondering if I could ask you a quick question? I'm confusing myself over the anode and cathode in electrochemical cells. I understand that electrons are 'produced' at the most negative half cell, and then these travel to the more positive half cell where they are then 'used', but I don't understand which electrode is which. For example, in a zinc-copper half cell, which electrode is the anode and which electrode is the cathode?
Thank you very much :smile:


No worries!


What you have to do is, for example like you stated the zinc-copper, we are given the electrode potential values, so if the electrode potential (the value in other words) is more positive than that would be the anode , if the electrode potential value is more negative than that would be the cathode.
So the electrode potental value for Zn is -0.76 V
and electrode potential value for Cu = + 0.34V

so from this data we can tell Cu will be the anode (positive) and the Zn is more negative , so this is the cathode( negative) and electrons flow from Zn to Cu


is this answering your questions? if not please tell me :smile:
(edited 10 years ago)
Reply 666
Avatar for zef1995
zef1995
10
Original post by otrivine
No worries!


What you have to do is, for example like you stated the zinc-copper, we are given the electrode potential values, so if the electrode potential (the value in other words) is more positive than that would be the anode , if the electrode potential value is more negative than that would be the cathode.
So the electrode potental value for Zn is -0.76 V
and electrode potential value for Cu = + 0.34V

so from this data we can tell Cu will be the anode (positive) and the Zn is more negative , so this is the cathode( negative) and electrons flow from Zn to Cu


is this answering your questions? if not please tell me :smile:


Thank you very much for that, I understand that the electrons flow from Zn to Cu as Zn has a more negative electrode potential value. As you mentioned, Cu is the anode in this case as it has the most positive electrode potential, and Zn is the cathode, but with respect to the powerpoint you posted, the image of the electrochemical cell shows Cu being the cathode and Zn being the anode. I'm not saying you're wrong, I was just wondering why this is - does one part of the half cell act as the anode, whilst the other part acts as a cathode?

I'm sorry if I'm getting the wrong end of the stick, but thank you for all of your help so far :smile:
Original post by zef1995
Thank you very much for that, I understand that the electrons flow from Zn to Cu as Zn has a more negative electrode potential value. As you mentioned, Cu is the anode in this case as it has the most positive electrode potential, and Zn is the cathode, but with respect to the powerpoint you posted, the image of the electrochemical cell shows Cu being the cathode and Zn being the anode. I'm not saying you're wrong, I was just wondering why this is - does one part of the half cell act as the anode, whilst the other part acts as a cathode?

I'm sorry if I'm getting the wrong end of the stick, but thank you for all of your help so far :smile:


I got the image from google? Cause it was nicely drawn. Let me check :smile:
Original post by zef1995
Thank you very much for that, I understand that the electrons flow from Zn to Cu as Zn has a more negative electrode potential value. As you mentioned, Cu is the anode in this case as it has the most positive electrode potential, and Zn is the cathode, but with respect to the powerpoint you posted, the image of the electrochemical cell shows Cu being the cathode and Zn being the anode. I'm not saying you're wrong, I was just wondering why this is - does one part of the half cell act as the anode, whilst the other part acts as a cathode?

I'm sorry if I'm getting the wrong end of the stick, but thank you for all of your help so far :smile:



Yes you are right, I should not trust google images will make the change :smile: well spotted
Reply 669
Avatar for zef1995
zef1995
10
Original post by otrivine
Yes you are right, I should not trust google images will make the change :smile: well spotted


Oh Google images :P
I've seen a few youtube clips on electrochemical cells, and they show the Zn electrode to be the anode and the Cu electrode to be the cathode just like the image from Google, although I'm not too sure why this is...my brain hurts :P

Thank you for everything though, and good luck with your revision! I'm guessing you're sitting F325 this summer too? :smile:
Original post by zef1995
Oh Google images :P
I've seen a few youtube clips on electrochemical cells, and they show the Zn electrode to be the anode and the Cu electrode to be the cathode just like the image from Google, although I'm not too sure why this is...my brain hurts :P

Thank you for everything though, and good luck with your revision! I'm guessing you're sitting F325 this summer too? :smile:




It depends cause maybe the expriments were not in their standard conditions and so could have affected the electrode potential value.

yes I am :smile:
Reply 671
Avatar for zef1995
zef1995
10
Original post by otrivine
It depends cause maybe the expriments were not in their standard conditions and so could have affected the electrode potential value.

yes I am :smile:


That's a very good point, if the experiments weren't done under standard conditions that would affect things.

Cool, good luck, I hope you achieve the grade you're hoping for :smile:
Original post by zef1995
That's a very good point, if the experiments weren't done under standard conditions that would affect things.

Cool, good luck, I hope you achieve the grade you're hoping for :smile:


exactly :smile:

would you like to revise
Reply 673
Avatar for zef1995
zef1995
10
Original post by otrivine
exactly :smile:

would you like to revise


Sure why not :smile:
Original post by zef1995
Sure why not :smile:


Define:standard electrode potential (3)
Reply 675
Avatar for zef1995
zef1995
10
Original post by otrivine
Define:standard electrode potential (3)


The standard electrode potential of a half cell is the e.m.f of a half cell compared to that of a standard hydrogen half cell. It is measured at 298K, with a gas pressure of 1 atm (100 kPa) and solution concentrations of 1 mol dm-3.

What is the hydrogen economy?
(I'm not sure how many marks it is - I'm making up the questions but I'll check any answers) :smile:
Original post by zef1995
The standard electrode potential of a half cell is the e.m.f of a half cell compared to that of a standard hydrogen half cell. It is measured at 298K, with a gas pressure of 1 atm (100 kPa) and solution concentrations of 1 mol dm-3.

What is the hydrogen economy?
(I'm not sure how many marks it is - I'm making up the questions but I'll check any answers) :smile:



Nice 3/3


Hydrogen economy is the storing of hydrogen as liquid under pressure and requires lots of energy and hence, following high production costs. It uses energy from fuel in reaction that uses oxygen to create a voltage. Adsorbed onto solid materials and absorbed within solid materials.
Reply 677
Avatar for zef1995
zef1995
10
Original post by otrivine
Nice 3/3


Hydrogen economy is the storing of hydrogen as liquid under pressure and requires lots of energy and hence, following high production costs. It uses energy from fuel in reaction that uses oxygen to create a voltage. Adsorbed onto solid materials and absorbed within solid materials.


Yay thank you :smile:

That all sounds correct to me! Although, the answer that is down in my textbook says that the hydrogen economy is the use of hydrogen as a basic fuel for everything, and then it goes on to describe the limitations and storage of hydrogen (which you have correctly described). :smile:
Original post by zef1995
Yay thank you :smile:

That all sounds correct to me! Although, the answer that is down in my textbook says that the hydrogen economy is the use of hydrogen as a basic fuel for everything, and then it goes on to describe the limitations and storage of hydrogen (which you have correctly described). :smile:



so what should I say :smile: I thought I mentioned fuel cell
Reply 679
Avatar for zef1995
zef1995
10
Original post by otrivine
so what should I say :smile: I thought I mentioned fuel cell


Although what you said was correct, you described what a fuel cell is and how the hydrogen can be stored; a hydrogen economy is the use of hydrogen as a basic fuel for everything. For example, we are in an oil economy at the moment, so we use fossil fuels to power our cars etc. In a hydrogen economy, hydrogen would be used instead of this :smile:

I hope that makes sense :smile:

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