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    This is from the June 2013R Unit 4 edexcel paper.
    When calculating the equilibrium concentration of a particular ion why do you have to do initial conc minus the equilibrium conc?
    E.g. in order to calculate Fe3+ equil conc. you had to calculate equil conc of Fe2+ and subtract it from initial conc of reaction mixture. Fe2+(aq) + Ag+(aq) ⇌ Fe3+(aq) + Ag(s)
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    (Original post by PlayerBB)
    Your exam is in 8 weeks, spend a week of your life and learn As organics like I suggest from the actual book then revise from the CGP. Organics is a really understandable topic if you put on the effort and the correct mid set to actually learn it instead of spending questions for waste


    Posted from TSR Mobile

    Yeah thanks I'll try. I've went over the alcohols part and it seems fairly understandable. I've looked over the spec and its mainly understanding the reactions.

    For this though i dont know to what extent i need to 'understand' the reaction. I can predict what will happen and ive memorised the reactions so is that it?
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    (Original post by haj101)
    You should be given values for either lattice dissociation or lattice formation and the enthalpy of hydration of lithium and fluoride.
    The equation is either:
    Lattice dissociation + hydration of fluoride + hydration of lithium
    Or
    -lattice formation + hydration of fluoride + hydration of lithium

    I don't know if that helped if you could post the question Ill help you
    I have posted the full question...

    Sorry for the confusion, for my exam you get given a data book filled will all sorts of tables and data you need for the full course. Found the relevant data in that now, thanks for that!
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    (Original post by Rtdsv)
    Posted from TSR Mobile

    Yeah thanks I'll try. I've went over the alcohols part and it seems fairly understandable. I've looked over the spec and its mainly understanding the reactions.

    For this though i dont know to what extent i need to 'understand' the reaction. I can predict what will happen and ive memorised the reactions so is that it?
    It's really great that you went through it! And yeah it's means like predicting what will happen, when we react this with that, what is the outcome, the conditions of the reaction and any mechanisms involved
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    (Original post by Zain-A)
    I have posted the full question...

    Sorry for the confusion, for my exam you get given a data book filled will all sorts of tables and data you need for the full course. Found the relevant data in that now, thanks for that!
    No problem
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    Has anyone done the AQA 6X EMPA yet? If so, how did you find it?
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    (Original post by Emily Thompson)
    I am! I've done both tasks
    Could you tell me how it was please?? I got a D last year and just can't afford to do that bad again


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    ive done chemsitry 6x Empã anyone who wants what we do tell me about biology 6x Empã
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    (Original post by Ladymusiclover)
    This is from the June 2013R Unit 4 edexcel paper.
    When calculating the equilibrium concentration of a particular ion why do you have to do initial conc minus the equilibrium conc?
    E.g. in order to calculate Fe3+ equil conc. you had to calculate equil conc of Fe2+ and subtract it from initial conc of reaction mixture. Fe2+(aq) + Ag+(aq) ⇌ Fe3+(aq) + Ag(s)
    That's because of the ratios

    There is a 1 to 1 ratio between the Fe2+ and the Fe3+

    In other words, for every x moles of Fe2+ I chuck into the reaction, I'm going to get x moles of Fe3+ out
    And vice versa.

    So I want to know the moles of the Fe3+ given the moles of Fe2+ at equilibrium.
    Well, I know the moles of Fe2+ which is whatever number you're given, say A
    And by my ratios, that must mean A moles of Fe3+ had to react to form that Fe2+.

    So from initial number of moles, only A moles reacted.
    Giving me the moles left at equilibrium.

    In other words, Initial - Reacted = Equilibrium

    This bit here...
    (Original post by Ladymusiclover)
    why do you have to do initial conc minus the equilibrium conc? ⇌ Fe3+(aq) + Ag(s)
    Equilibrium conc. refers to the moles of the reactant that reacted to form the product that is now at equilibrium.
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    A moment of silence to whomever had made this thread. THANK YOU YOU'VE JUST SAVED MY FUTURE.
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    (Original post by RMNDK)
    That's because of the ratios

    There is a 1 to 1 ratio between the Fe2+ and the Fe3+

    In other words, for every x moles of Fe2+ I chuck into the reaction, I'm going to get x moles of Fe3+ out
    And vice versa.

    So I want to know the moles of the Fe3+ given the moles of Fe2+ at equilibrium.
    Well, I know the moles of Fe2+ which is whatever number you're given, say A
    And by my ratios, that must mean A moles of Fe3+ had to react to form that Fe2+.

    So from initial number of moles, only A moles reacted.
    Giving me the moles left at equilibrium.

    In other words, Initial - Reacted = Equilibrium

    This bit here...
    Equilibrium conc. refers to the moles of the reactant that reacted to form the product that is now at equilibrium.
    Thanks so much. I understand it now.
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    Does anyone know the reactions of SO2 with NaOH?
    I'm getting mixed messages. I've been told it happens in 2 steps like follows in one book:
    SO2 + NaOH --> NaHSO3
    NaHSO3 + NaOH --> Na2SO3 + H2O

    And somewhere else has said:
    NaOH + SO2 --> Na2SO3 + H2O
    Na2SO3 + H2O + SO2 --> 2NaHSO3
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    (Original post by Thisshouldbeapun)
    Does anyone know the reactions of SO2 with NaOH?
    I'm getting mixed messages. I've been told it happens in 2 steps like follows in one book:
    SO2 + NaOH --> NaHSO3
    NaHSO3 + NaOH --> Na2SO3 + H2O

    And somewhere else has said:
    NaOH + SO2 --> Na2SO3 + H2O
    Na2SO3 + H2O + SO2 --> 2NaHSO3
    SO2 + 2NaOH ___> NaSO3 + H2O is right

    I dont think you need to know the second reaction of sodium hydrogen sulfate with water, its not in the spec (might be mistaken) but you only need to know that sulfur dioxide can act as a base and acid
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    The question asks to name this compound, it says the answer is 2-ethoxybutane, but should it not be 2, methyl-ethoxypropane?

    Also just noticed this, how tf does the CH2 carbon have 5 bonds?!? Is this question completely wrong or am I missing something major here?
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    (Original post by Zain-A)



    The question asks to name this compound, it says the answer is 2-ethoxybutane, but should it not be 2, methyl-ethoxypropane?

    Also just noticed this, how tf does the CH2 carbon have 5 bonds?!? Is this question completely wrong or am I missing something major here?
    Uh oh, we can't see the image.
    Try reposting again.
    Or perhaps a link instead?
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    (Original post by chzm)
    SO2 + 2NaOH ___> NaSO3 + H2O is right

    I dont think you need to know the second reaction of sodium hydrogen sulfate with water, its not in the spec (might be mistaken) but you only need to know that sulfur dioxide can act as a base and acid
    Careful..
    Your Sodium isn't balanced.
    i.e. should be Na2SO3

    Also, how does SO2 act as a base and an acid? It's not amphoteric; only an acidic oxide.
    Are you sure you weren't thinking of SiO2..?
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    (Original post by Science_help)
    Lets see who gets this right.
    No using google or textbook btw.

    What temperature does diamond melt at ? nearest 100
    +650 degree celcius
    so probably 700 degree celcius
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    Hi people, Chemistry student at University here.
    Got an A* in alevel so if anyone has any questions or whatever, feel free to ask them.


    Love to help
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    Hi, How do you balance two half equations when you have water and H+'s on both sides of the two equations after you have balanced their electrons
    For example:
    1. 5V3+ + 15H2O ------> 5VO3- + 30H+ + 10e-
    2. 2MnO4- + 16H+ + 10e- -------> 2Mn2+ + 8H20

    Hope you can help
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    (Original post by Cobalt_)
    Hi people, Chemistry student at University here.
    Got an A* in alevel so if anyone has any questions or whatever, feel free to ask them.


    Love to help
    Pleasure to come across you again on the Chem forums ;D

    I have some quite a long winded question about the Arrhenius equation. I need to be able to work out the Ea of a reaction using the rate of reaction, and the temperature, forming a graph of X axis 1/T ( kelvin) and Y axis ln 1/t ( time, seconds). I think time is used as it is proportional to the rate constant, k.
    When you solve for the gradient of the graph, the standard dy / dx, do you need to also solve for the units of the gradient?
    My own workings got me s K^-1, but on other websites I have seen units of gradient as being K, i'm just a bit confused about this part of the course generally.
    Another thing that is irritating me is A, the " pre-exponential factor", again from what i've been able to garner from various videos and websites is that it becomes the Y intercept when you put the whole equation into the y = mx + c form, but I still have no clue as to what it is and how it relates to the rate or activation energy.
 
 
 
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