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    (Original post by L'Evil Fish)
    Just remember...

    Oxygen + Water + Electrons = Hydroxide Ions

    O(2) + 4H(2)O + 4e- = 4OH-

    Hydroxide Ions + Hydrogen = Water + Electrons

    4OH- + 2H(2) ---> 2H(2)O + 4e-

    _

    What help do you need with them?
    CFC's- why's there a continuous depletion of O(3)?
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    (Original post by L'Evil Fish)
    I think there's a mistake in the CGP book.

    Page 93

    2. So they are attracted to the negative anode and are reduced to copper atoms....

    :lolwut:
    Oh yeah! It should just be "negative cathode" I'm pretty sure, that's how it is in the picture.
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    Failing Chemistry
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    (Original post by benwalters1996)
    CFC's- why's there a continuous depletion of O(3)?
    Because Cl O ¤ (¤ is my radical sign :lol:) is never used up in the process.

    ClO¤ + O(3) ---> 2O(2) + Cl ¤

    Cl ¤ + O(3) ---> ClO¤ + O(2)

    And it happens repeatedly.

    (Original post by cameron262)
    Oh yeah! It should just be "negative cathode" I'm pretty sure, that's how it is in the picture.
    :lol: silly book
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    last year the raw marks (out of 60) were 19 for a c, 28 for a b, 37 for a, 46 for a*

    which i think are fairly low, do you all think that will be consistent this year, or that the grade boundaries will be higher/lower?
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    (Original post by foyzx)
    last year the raw marks (out of 60) were 19 for a c, 28 for a b, 37 for a, 46 for a*

    which i think are fairly low, do you all think that will be consistent this year, or that the grade boundaries will be higher/lower?
    55 will probably be an A* due to the section D, add 5/6 to each 2012 grade boundary i reckon.
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    If i got a b in c123 and an a in c/w, wat mark will i need to get a b overall in tmrws exam?

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    (Original post by foyzx)
    last year the raw marks (out of 60) were 19 for a c, 28 for a b, 37 for a, 46 for a*

    which i think are fairly low, do you all think that will be consistent this year, or that the grade boundaries will be higher/lower?
    It was out of 75

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    (Original post by AR-13)
    If i got a b in c123 and an a in c/w, wat mark will i need to get a b overall in tmrws exam?

    Posted from TSR Mobile
    What UMS ???

    What mark ???
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    can someone explain to me why weak acids do not completely ionise in water- i know it's because it's a reversible reaction but i don't really understand? xx thank you
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    (Original post by izzzyyay)
    can someone explain to me why weak acids do not completely ionise in water- i know it's because it's a reversible reaction but i don't really understand? xx thank you
    hi

    this video explains it very nicely:
    http://www.youtube.com/watch?v=Np-jOY_EshQ
    skip to about 2mins or you'll get bored by his voice -.-
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    (Original post by izzzyyay)
    can someone explain to me why weak acids do not completely ionise in water- i know it's because it's a reversible reaction but i don't really understand? xx thank you
    I'll give you an example -

    The chemical formula for ethanoic acid is CH3COOH. The underlined H is the hydrogen atom that becomes an ion in water as it loses an electron, becoming H+ .

    However, the other Hydrogen ions (CH3COOH) do not ionise (it's something to do with the bonding between the different elements but don't worry about that) so out of the 4 Hydrogen atoms in the chemical formula, only 1 ionises. Because of this, the concentration of Hydrogen atoms in the acid that ionise is low.

    CH3COOH -> CH3COO- + H+

    As you can see there are still 3 Hydrogen atoms that haven't ionised and become positive ions. An equilibrium mixture is formed (the arrow is supposed to be reversible by the way)

    But hydrochloric acid which has the formula HCl, has its single Hydrogen atom ionise in water. Therefore, the concentration of Hydrogen atoms in hydrochloric acid that ionise is high.

    HCl ->H++Cl-

    As you can see all of the Hydrogen atoms in HCl ionise, so it is a strong acid.

    I'm not sure if this is what you were looking for, but hopefully it should clarify some things...?
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    (Original post by BP_Tranquility)
    I'll give you an example -

    The chemical formula for ethanoic acid is CH3COOH. The underlined H is the hydrogen atom that becomes an ion in water as it loses an electron, becoming H+ .

    However, the other Hydrogen ions (CH3COOH) do not ionise (it's something to do with the bonding between the different elements but don't worry about that) so out of the 4 Hydrogen atoms in the chemical formula, only 1 ionises. Because of this, the concentration of Hydrogen atoms in the acid that ionise is low.

    CH3COOH -> CH3COO- + H+

    As you can see there are still 3 Hydrogen atoms that haven't ionised. An equilibrium mixture is formed (the arrow is supposed to be reversible by the way)

    But hydrochloric acid which has the formula HCl, has its single Hydrogen atom ionise in water. Therefore, the concentration of Hydrogen atoms in hydrochloric acid that ionise is high.

    HCl ->H++Cl-

    As you can see all of the Hydrogen atoms in HCl ionise, so it is a strong acid.

    I'm not sure if this is what you were looking for, but hopefully it should clarify some things...?
    picking up from earlier-where about are you with education? because this all seems quite advanced(or maybe i'm oversimplifying the GCSE :eek: ).

    as for weak acids-are the reactions always reversible?

    ps-please say you and L'Evil Fish are this good at physics too?
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    (Original post by BP_Tranquility)
    I'll give you an example -

    The chemical formula for ethanoic acid is CH3COOH. The underlined H is the hydrogen atom that becomes an ion in water as it loses an electron, becoming H+ .

    However, the other Hydrogen ions (CH3COOH) do not ionise (it's something to do with the bonding between the different elements but don't worry about that) so out of the 4 Hydrogen atoms in the chemical formula, only 1 ionises. Because of this, the concentration of Hydrogen atoms in the acid that ionise is low.

    CH3COOH -> CH3COO- + H+

    As you can see there are still 3 Hydrogen atoms that haven't ionised and become positive ions. An equilibrium mixture is formed (the arrow is supposed to be reversible by the way)

    But hydrochloric acid which has the formula HCl, has its single Hydrogen atom ionise in water. Therefore, the concentration of Hydrogen atoms in hydrochloric acid that ionise is high.

    HCl ->H++Cl-

    As you can see all of the Hydrogen atoms in HCl ionise, so it is a strong acid.

    I'm not sure if this is what you were looking for, but hopefully it should clarify some things...?


    thank you so much! xx
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    (Original post by benwalters1996)
    picking up from earlier-where about are you with education? because this all seems quite advanced(or maybe i'm oversimplifying the GCSE :eek: ).

    as for weak acids-are the reactions always reversible?

    ps-please say you're this good at physics too?
    No, I'm still doing GCSE
    I was here on the forums quite a lot for the biology exams but today, I had some other exams so I was focusing on them rather than chemistry.

    Well, I'm quite interested in science so tend to read around the subject quite a lot in my spare time, but the above was mainly from my revision guide. From my understanding, weak acids are usually reversible due to something about the attractions between the different elements...

    I've read somewhere that weak acids form an equilibrium mixture because the ions produced in ethanoic acid when it breaks down into CH3COO- and H+ are not stable so they have the potential to bond back together and form ethanoic acid again. Hydrochloric acid however breaks down into H+ and Cl- ions which are more stable and prevents an equilibrium to be formed. :cool:

    Haha, not sure if I'm as good at physics but it is my favourite science but I guess we'll find out.
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    GUYS HELP

    you know the fuel cell equations?

    my book taught me that in acid conditions

    ANODE

    H2 + 2OH- - 2e- -> 2H2O


    CATHODE

    O2 + 2H2O + 4e- -> 4OH-


    HOWEVER the specimen mark scheme said

    positive (+ve) electrode: O2 + 2H2O + 4e- -> 4OH-


    negative (-ve) electrode: H2 + 2OH- -> 2H2O + 2e-


    WHAT? which one is right!?
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    (Original post by NatashaG)
    GUYS HELP

    you know the fuel cell equations?

    my book taught me that in acid conditions

    ANODE

    H2 + 2OH- - 2e- -> 2H2O


    CATHODE

    O2 + 2H2O + 4e- -> 4OH-


    HOWEVER the specimen mark scheme said

    positive (+ve) electrode: O2 + 2H2O + 4e- -> 4OH-


    negative (-ve) electrode: H2 + 2OH- -> 2H2O + 2e-


    WHAT? which one is right!?
    I learnt:

    O(2) + 2H(2)O + 4e- ---> 4OH-
    4OH- + 2H(2) ---> 2H(2)O + 4e-

    Which overall is:

    2H(2) + O(2) ---> 2H(2)O
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    (Original post by NatashaG)
    GUYS HELP

    you know the fuel cell equations?

    my book taught me that in acid conditions

    ANODE

    H2 + 2OH- - 2e- -> 2H2O


    CATHODE

    O2 + 2H2O + 4e- -> 4OH-


    HOWEVER the specimen mark scheme said

    positive (+ve) electrode: O2 + 2H2O + 4e- -> 4OH-


    negative (-ve) electrode: H2 + 2OH- -> 2H2O + 2e-


    WHAT? which one is right!?
    Well, believe it or not, but I was told that they were both correct!

    My revision guide says:
    negative electrode: 2H2-->4H+ +4e-
    positive electrode: 4H+ +4e- +O2-->2H2O

    But apparently the different equations are different because they give you the reactions from a different perspective- e.g. your revision guide's reactions may be from positive to negative electrode whilst mine's could be from the negative to positive electrode. I'm not sure how this affects the equations though but this was what I was told. If I were you, I would learn the equations in your revision guide since there's a chance the specimen is wrong :cool:
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    (Original post by L'Evil Fish)
    I learnt:

    O(2) + 2H(2)O + 4e- ---> 4OH-
    4OH- + 2H(2) ---> 2H(2)O + 4e-

    Which overall is:

    2H(2) + O(2) ---> 2H(2)O
    that's what it says in the revision book

    i wouldn't trust the mark scheme, for Q1 it said 'expected answer:nitrogen' 'additional guidance: Mg is acceptable' which..as far as i know...is wrong?
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    (Original post by benwalters1996)
    that's what it says in the revision book

    i wouldn't trust the mark scheme, for Q1 it said 'expected answer:nitrogen' 'additional guidance: Mg is acceptable' which..as far as i know...is wrong?
    :lol: fair enough, but the book has mistakes too
 
 
 
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