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OCR Chemistry A Exam Thread (Breadth - May 27 2016 and Depth - June 10 2016) Watch

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    (Original post by kiwifruit99)
    Is shapes of molecules likely to come up?
    I think so.
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    (Original post by 4nonymous)
    yes, free radical substitution is homolytic
    electophilic addition and nucleophillic substitution are heterolytic
    How comes the nucleophilic substitution is heterolytic? Doesn't the chlorine atom take both electrons. Oh wait lol. I got my definition mixed up looool. Homolytic fission take one electron.
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    Heterolytic is where one atom takes both of the electrons in an uneven split so ions form
    Homolytic is the even split so both atoms end up with an unpaired electron and thus are radicals

    (Original post by Cherx)
    How comes the nucleophilic substitution is heterolytic? Doesn't the chlorine atom take both electrons.
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    anyone got list of possible practical questions?
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    (Original post by Cherx)
    How comes the nucleophilic substitution is heterolytic? Doesn't the chlorine atom take both electrons. Oh wait lol. I got my definition mixed up looool. Homolytic fission take one electron.
    Yes, homolytic forms free radicals so thats why its used for free radical substitution. Heterolytic is when one of the atoms receives both electrons.
    lol you almost confused me for a sec too.
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    (Original post by JamieHarris1998)
    Heterolytic is where one atom takes both of the electrons in an uneven split so ions form
    Homolytic is the even split so both atoms end up with an unpaired electron and thus are radicals
    Last minute stress loool. Forgetting everything. Really don't want titrations to come up. If you go over the meniscus line the concentration of the known solution decreases doesn't it?
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    We had a few titration calculations to do in the last paper so maybe other maths questions will come up instead
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    (Original post by asinghj)
    Combustion and bond enthalpies is reactants - products
    Formation is the odd one out so products - reactants
    So if they give us a table of formation values to work out combustion, would you do products- reactants?! Or the other way around?
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    (Original post by JamieHarris1998)
    We had a few titration calculations to do in the last paper so maybe other maths questions will come up instead
    Ah I was thinking they might ask about the practical aspect of it. Can't really think of some other practical's they could ask.
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    (Original post by Jitesh)
    Ah, I see now - so it is to do with the molar quantities

    Why does it show adding the sum of the stoichiometric number of entity B?

    Edit: nevermind misread it

    Thanks a bunch! Not seen a question like that before lol
    Hey, I done this question and got the same answer as you and I don't really understand the Wikipedia article. Could you explain it please?
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    what definitions do we need to know?
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    Maybe asking about how to set up oxidation/distilliation of alcohols or the practical we did about testing for ions because we only mentioned the colours of precipitates last exam. But titrations aren't too bad to setup, the process if ok but just tricky to remember the small steps and the equipment

    (Original post by Cherx)
    Ah I was thinking they might ask about the practical aspect of it. Can't really think of some other practical's they could ask.
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    (Original post by Cherx)
    Ah I was thinking they might ask about the practical aspect of it. Can't really think of some other practical's they could ask.
    There are others they could ask such as:
    oxidation of alcohols
    calorimetry
    Tests for ammonia, sulfates, halides etc
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    (Original post by amysed)
    what definitions do we need to know?
    Who knows. Could be any of them but the most probable are relative atomic mass, isotopes and isomers.
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    Do we need to know about the history of the periodic table for this exam?
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    (Original post by JamieHarris1998)
    Maybe asking about how to set up oxidation/distilliation of alcohols or the practical we did about testing for ions because we only mentioned the colours of precipitates last exam. But titrations aren't too bad to setup, the process if ok but just tricky to remember the small steps and the equipment
    (Original post by 4nonymous)
    There are others they could ask such as:
    oxidation of alcohols
    calorimetry
    Tests for ammonia, sulfates, halides etc
    Oh gosh I have so many to go over know. Actually Ik the ammonium ion test. How does the sulfate one work?

    Calorimetry? Isnt that bio?

    O2 of alchols is not too bad... I think. When you say set up though? As in the equipment? So anti bumbing granules (idk why I can remember this), condenser, heat bath?

    Yeah I'm gonna count on the fact they don't give titration as we did have a 3 marker on it in the last paper.
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    (Original post by Cherx)
    Oh gosh I have so many to go over know. Actually Ik the ammonium ion test. How does the sulfate one work?

    Calorimetry? Isnt that bio?

    O2 of alchols is not too bad... I think. When you say set up though? As in the equipment? So anti bumbing granules (idk why I can remember this), condenser, heat bath?

    Yeah I'm gonna count on the fact they don't give titration as we did have a 3 marker on it in the last paper.
    The sulfate one is when you add barium chloride solution and you get barium sulfate which is a white precipitate.

    Calorimetry is the experiment with the polystyrene cup and spirit burner.

    As for alcohols I think you need to know the setting up equipment for distillation and reflux which I still need to go over.
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    (Original post by Cherx)
    Oh gosh I have so many to go over know. Actually Ik the ammonium ion test. How does the sulfate one work?

    Calorimetry? Isnt that bio?

    O2 of alchols is not too bad... I think. When you say set up though? As in the equipment? So anti bumbing granules (idk why I can remember this), condenser, heat bath?

    Yeah I'm gonna count on the fact they don't give titration as we did have a 3 marker on it in the last paper.
    Test for sulfates is adding dilute HCl then BaCl and if a white precipitate forms a sulfate is present.
    I can't remember the calorimetry test
    Oxidation might ask about why we reflux (prevents the loss of volatile liquids by preventing the evapourated liquids from escaping by condensing them back).
    Also about why we left the top open, which was to prevent explosions from pressure created by heating gas which would be danagerous if sealed by a stopper when condensing
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    (Original post by Normy18)
    Do we need to know about the history of the periodic table for this exam?
    Don't think so.
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    (Original post by 4nonymous)
    The sulfate one is when you add barium chloride solution and you get barium sulfate which is a white precipitate.

    Calorimetry is the experiment with the polystyrene cup and spirit burner.

    As for alcohols I think you need to know the setting up equipment for distillation and reflux which I still need to go over.
    Oh gosh not that.. Hoping they don't ask of calorimetry I mean they did have quite a hefty calculation question on it.

    Ah ok. I need to go over it too. Lmao I'm going over so many stuff rn. The only green chemistry we have is the polymer stuff isn't it? So waste polymers you could make into other new polymer, sort and recycle, organic feedstock.
 
 
 
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