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Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread watch

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    (Original post by Sadiariya)
    Hey, can anyone explain to me when to put water into an equilibrium equation and when to leave it out?
    The reason water is left out of equilibrium calculations is that it's normally in such an excess that its concentration effectively doesn't change. So the only time you'd put it in as far as I can think of in any of these papers is when it's formed as a product, such as in an esterification reaction.
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    (Original post by Spoderman14)
    The reason water is left out of equilibrium calculations is that it's normally in such an excess that its concentration effectively doesn't change. So the only time you'd put it in as far as I can think of in any of these papers is when it's formed as a product, such as in an esterification reaction.
    Okay great, thank you!
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    (Original post by Don Pedro K.)
    Haha yeah I did decent in it (78/90). you guys probably got high 80s or something but
    80/90 Too many careless mistakes. :lol:

    (Original post by samb1234)
    I haven't done any unit 5 papers yet ill do some in the next few days. At least I have quite a big margin for error if a paper is filthy thankfully
    What do you mean big margin for error? AS UMS or ISA?
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    (Original post by Ayman!)
    80/90 Too many careless mistakes. :lol:



    What do you mean big margin for error? AS UMS or ISA?
    Both. I only really need an A for my offer (although an A* would be nice and I would be a bit disappointed if i didn't get one) and im currently on something like 350 ish so it's not the end of the world if one goes badly. Need 210 from the exams for a* though so hopefully will be able to do that
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    [QUOTE=Ayman!;65651943]80/90 Too many careless mistakes. :lol:


    Ayman, have you tried Jan 16?
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    (Original post by Ayman!)
    80/90 Too many careless mistakes. :lol:



    What do you mean big margin for error? AS UMS or ISA?
    Lol nice xD!
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    (Original post by samb1234)
    Both. I only really need an A for my offer (although an A* would be nice and I would be a bit disappointed if i didn't get one) and im currently on something like 350 ish so it's not the end of the world if one goes badly. Need 210 from the exams for a* though so hopefully will be able to do that
    Is your offer A*A*AA with the A*s in two? If so, you already have it with M and FM (which are absolute gifts in comparison to physics and chem haha). Must be neat to have full on the ISA knowing you have a few marks to spare.

    (Original post by sabahshahed294)
    Ayman, have you tried Jan 16?
    I have a long time back, but I will do it as a mock tonight! I remember it to be quite a straightforward one. Jan 16, June 15 (UK and IAL) are the only ones I have left from 2012-2016. Feeling somewhat alright for U4 now.

    (Original post by Don Pedro K.)
    Lol nice xD!
    Thanks for the paper fam! The equilibrium question was quite nice. If only I looked over it before my Unit 6. :cry:
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    [QUOTE=Ayman!;65652653]Is your offer A*A*AA with the A*s in two? If so, you already have it with M and FM (which are absolute gifts in comparison to physics and chem haha). Must be neat to have full on the ISA knowing you have a few marks to spare.

    (Original post by sabahshahed294)

    I have a long time back, but I will do it as a mock tonight! I remember it to be quite a straightforward one. Jan 16, June 15 (UK and IAL) are the only ones I have left from 2012-2016. Feeling somewhat alright for U4 now.



    Thanks for the paper fam! The equilibrium question was quite nice. If only I looked over it before my Unit 6. :cry:
    Yeah that is my offer, so should be good provided I don't massively mess up the rest of my exams
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    [QUOTE=Ayman!;65652653]Is your offer A*A*AA with the A*s in two? If so, you already have it with M and FM (which are absolute gifts in comparison to physics and chem haha). Must be neat to have full on the ISA knowing you have a few marks to spare.

    (Original post by sabahshahed294)

    I have a long time back, but I will do it as a mock tonight! I remember it to be quite a straightforward one. Jan 16, June 15 (UK and IAL) are the only ones I have left from 2012-2016. Feeling somewhat alright for U4 now.



    Thanks for the paper fam! The equilibrium question was quite nice. If only I looked over it before my Unit 6. :cry:
    Haha no problem dude I flipping messed it up though because I didn't realise that the NaOH reacts with the EQUILIBRIUM mixture and not the original one lol...Oh well you learn from your mistakes right ?!
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    (Original post by Ayman!)
    Is your offer A*A*AA with the A*s in two? If so, you already have it with M and FM (which are absolute gifts in comparison to physics and chem haha). Must be neat to have full on the ISA knowing you have a few marks to spare.



    I have a long time back, but I will do it as a mock tonight! I remember it to be quite a straightforward one. Jan 16, June 15 (UK and IAL) are the only ones I have left from 2012-2016. Feeling somewhat alright for U4 now.



    Thanks for the paper fam! The equilibrium question was quite nice. If only I looked over it before my Unit 6. :cry:
    Oh nice! I have 14 and 15 to go! U4 seems descent than U5
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    Can someone explain something. I dont understand the affect heating has on the pH of water. Does it become acidic when you heat it?
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    Thank you soooo much! This is exactly what I needed!!! btw. what book is this from?
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    [QUOTE=samb1234;65652751]
    (Original post by Ayman!)
    Is your offer A*A*AA with the A*s in two? If so, you already have it with M and FM (which are absolute gifts in comparison to physics and chem haha). Must be neat to have full on the ISA knowing you have a few marks to spare.



    Yeah that is my offer, so should be good provided I don't massively mess up the rest of my exams
    I'm not sure if you've mentioned it in a post before but where is your A*A*AA offer for? If you don't mind me asking
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    (Original post by CLGC98)
    Can someone explain something. I dont understand the affect heating has on the pH of water. Does it become acidic when you heat it?
    This is how I understand it

    Pure water disassociates into H+ and OH-. This is an endothermic reaction so increasing the temperature would favour the disassociation into H2O's constituent ions.

    Kw = [H+][OH-] so as the temperature increases, the conc of constituent ions increase, and so does Kw. From this, we can see that the pH is changing, but whether it's acidic or alkaline is a different story. The ratio of H+ and OH- ions will still remain the same regardless the pH in this case and so the water remains neutral (once again, the pH is not affecting it's acidity).
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    (Original post by CLGC98)
    Can someone explain something. I dont understand the affect heating has on the pH of water. Does it become acidic when you heat it?
    In all aqueous solutions and pure water the following equilibrium occurs:
    H2O (l) (reversible arrow) <---> H+(aq) + OH-(aq)

    At different temperatures to 25oC/298K the pH of pure water changes.
    Le Chatelier’s principle can predict the change.

    The dissociation of water is endothermic so increasing the temperature would push the equilibrium to the right giving a bigger concentration of H+ ions and so a lower pH.

    It is still neutral though as [H+(aq)] = [OH-(aq)]
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    (Original post by dj3k)
    Thank you soooo much! This is exactly what I needed!!! btw. what book is this from?
    It's George Facer A2 Chemistry
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    (Original post by ayvaak)

    I'm not sure if you've mentioned it in a post before but where is your A*A*AA offer for? If you don't mind me asking
    Cambridge
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    (Original post by samb1234)

    Yeah that is my offer, so should be good provided I don't massively mess up the rest of my exams
    Where's your offer from?
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    (Original post by Whizbox)
    Where's your offer from?
    Cambridge.
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    (Original post by samb1234)
    Cambridge
    Congrats
 
 
 

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