Chemistry unit 6 June 2016

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    (Original post by PlayerBB)
    Ahhh so it is in the dichloromethane, I got so confused because I thought the mark scheme was saying that each one will form a layer, okay thanks!

    Ah another question, how shall I know that it forms the bottom layer ?

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    The density is given (1.32 gcm^-3) which is greater than water's density, which is 1 gcm^-3, so more dense layers settle to the bottom!
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    (Original post by RizK)
    Get the specification first.

    From these, you have to learn: (where each number below is a point on the specification - read through the specification and you'll understand)
    Unit4:
    4.3c, 4.3e, 4.4g, 4.8.2c, 4.8.3d, 4.8.4.b, 4.4.4c.
    Unit5:
    5.3.1d, 5.3.1g, 5.3.2g, 5.3.2j, 5.4.1d, 5.4.2b, 5.4.2d, 5.4.2i, 5.4.3f.

    that is a lot.
    And it helps to know to know background theory too. According to my teacher edexcel likes to test theory through practicals.

    ninja edit: I got these from an old mapping document when the syllabus changed. I'm so grateful i decided to highlight them on my copy of the specification, because i lost the file.
    Thank you!!
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    (Original post by Adorable98)
    Could someone answer this please?
    well, when we add a quenching agent to the reaction mixture the reaction slows down but doesn't stop. As mentioned in step 4 (The propanone slows but does not completely stop the reaction.) so the reaction is still going on but at a slower rate, now if we don't titrate them immediately, more reaction would have occured and more NaOH used up, so lesser NaOH remains than we expected and hence lesser HCl is needed to react with it, so the titre would be too low!
    Makes sense?
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    (Original post by Aimen.)
    well, when we add a quenching agent to the reaction mixture the reaction slows down but doesn't stop. As mentioned in step 4 (The propanone slows but does not completely stop the reaction.) so the reaction is still going on but at a slower rate, now if we don't titrate them immediately, more reaction would have occured and more NaOH used up, so lesser NaOH remains than we expected and hence lesser HCl is needed to react with it, so the titre would be too low!
    Makes sense?
    Yes, it does. Thanks Aimen.
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    (Original post by Aimen.)
    well, when we add a quenching agent to the reaction mixture the reaction slows down but doesn't stop. As mentioned in step 4 (The propanone slows but does not completely stop the reaction.) so the reaction is still going on but at a slower rate, now if we don't titrate them immediately, more reaction would have occured and more NaOH used up, so lesser NaOH remains than we expected and hence lesser HCl is needed to react with it, so the titre would be too low!
    Makes sense?
    Yes!! Thank you!! But could we get asked to name any quenching agents??
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    January 16 was not nice. :cry:
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    (Original post by Ayman!)
    January 16 was not nice. :cry:
    Haven't solved it yet but the grade boundaries were way low for this paper :eek:
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    (Original post by Aimen.)
    The density is given (1.32 gcm^-3) which is greater than water's density, which is 1 gcm^-3, so more dense layers settle to the bottom!
    Ah, thanks Aimen!
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    what apparatus do we use for boiling point determination?
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    (Original post by PlayerBB)
    Haven't solved it yet but the grade boundaries were way low for this paper :eek:
    Do it, it's really different. I managed 60/60 UMS but my raw marks were horrendous.
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    (Original post by Ayman!)
    Do it, it's really different. I managed 60/60 UMS but my raw marks were horrendous.
    Ayman, if you managed 60/60 UMS..It's still something you managed lol
    I scored 50/60 in UMS
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    (Original post by Adorable98)
    Yes!! Thank you!! But could we get asked to name any quenching agents??
    Well I was very worried about this so I asked my teacher, he says "anything that would react with one of the reactants would work, because another reaction would occur"
    The most common is NaHCO3 for Iodine-thiosulfate titration!
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    (Original post by Ayman!)
    January 16 was not nice. :cry:
    Haha yea it was BAD!
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    (Original post by Aimen.)
    Well I was very worried about this so I asked my teacher, he says "anything that would react with one of the reactants would work, because another reaction would occur"
    The most common is NaHCO3 for Iodine-thiosulfate titration!
    I see, thanks once again!!!!!!
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    (Original post by baebae)
    what apparatus do we use for boiling point determination?
    Here you go!
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    (Original post by Aimen.)
    Well I was very worried about this so I asked my teacher, he says "anything that would react with one of the reactants would work, because another reaction would occur"
    The most common is NaHCO3 for Iodine-thiosulfate titration!
    There are other ways of quenching e.g. removing catalysts cooling it down adding alkali/acid then back titrating etc etc
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    (Original post by Ayman!)
    Do it, it's really different. I managed 60/60 UMS but my raw marks were horrendous.
    Congrats! Yeah I'll surely do it if I had time today!:argh:
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    (Original post by samb1234)
    There are other ways of quenching e.g. removing catalysts cooling it down adding alkali/acid then back titrating etc etc
    Yea I've been reading most of these but cooling just slows, not really stops!
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    (Original post by Aimen.)
    Yea I've been reading most of these but cooling just slows, not really stops!
    Thats fine for a lot of reactions when you stick them in ice d[a]/dt is basically 0, which is the whole point of quenching i.e. you don't have to stop the reaction, you just have to slow it to the point where the chance in conc by the time you measure it is insignificant, so things like cooling diluting etc etc are valid ways to do it
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    (Original post by Aimen.)
    Name:  20160515_221504.jpg
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    Here you go!
    Name:  1463337242187.jpg
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    Also another method of drawing it!

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