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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    (Original post by posthumus)
    Hopefully the grade boundaries will be quite low then I work so bloody hard towards chemistry exams and I've walked out of every single one in complete misery I got well below 50 out of 80 last year in Jan... the only reason I got 88 UMS was due to the ridiculously low grade boundaries

    Yup Basically I haven't made it any "easier" to get my B overall with my other exam, which is a shame really Are you sitting Unit 4 as well as 2 & 5? If you don't mind myself asking
    Yeah, I am. I've been crashing through 6CH02 papers and every possible worksheet in the world hoping to gain the maximum UMS I possibly can.

    I'm hoping the 6CH04 paper will be nicer than the January one! I'm not too worried about 6CH05, it's fairly synoptic without too much new information. Are you feeling prepared overall?

    If I miss my offer for university, it will be because of chemistry. That's my only fear!
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    Hey does anyone know, if you use a catalyst, wether the sum of the 2 new activation energies is equal to the original activation energy of the reaction?
    (Sorry, but of a wordy question)
    Thanks x
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    (Original post by HarryMWilliams)
    Yeah, I am. I've been crashing through 6CH02 papers and every possible worksheet in the world hoping to gain the maximum UMS I possibly can.

    I'm hoping the 6CH04 paper will be nicer than the January one! I'm not too worried about 6CH05, it's fairly synoptic without too much new information. Are you feeling prepared overall?

    If I miss my offer for university, it will be because of chemistry. That's my only fear!
    I'm going to start some "hardcore" chemistry unit 2 revision over the weekend then past papers for the following days leading up to the exam. I also have unit 2 physics, but my chemistry unit 2 is much much more important

    I've reached Acid-base chapter 5 in the George Facer book for unit 4... I'll probably finish reading through this today. Then possibly get some calculation done from the Jim Clark book, if not today then tomorrow I haven't had many issues with unit 4... just re-jogging my memory really

    I'm leaving chapter 6,7,8 & 9 towards the exam itself on the 12th as I think there's more memorizing involved there. But also anything from those particularly can come up in unit 5 While I do that I'm going to slip some unit 5 into my revision also

    I have a good feeling about unit 4 (though I've done least preparation for it in the past month). I am worried about unit 2 & 5 just as much. It's always on the exam day I like truly find out how hard Chemistry A-level is It's a subject that was never for me

    I feel the same If I don't get into university the blame will all be on Chemistry!! I spend all my time on it... and all I have asked for is a B. It's proving insanely difficult
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    (Original post by sophiekutie)
    Hey does anyone know, if you use a catalyst, wether the sum of the 2 new activation energies is equal to the original activation energy of the reaction?
    (Sorry, but of a wordy question)
    Thanks x
    Not quite sure what you mean

    A catalyst finds an alternative route which has a lower activation energy.

    I've never come across where there's 2 new activation energies
    Where'd you get this from ?
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    (Original post by posthumus)
    Not quite sure what you mean

    A catalyst finds an alternative route which has a lower activation energy.

    I've never come across where there's 2 new activation energies
    Where'd you get this from ?
    I mean in terms of this type of diagram...
    Name:  image.jpg
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    Would E' + E'' = the un-catalysed activation energy ?
    (Apologies for the picture, it's a picture of my revision guide)
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    (Original post by posthumus)
    x
    Kudos, let me know how you get on.
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    Can somebody tell me: Is it reflux or distillation apparatus that's used when making a ketone from a secondary alcohol? Because the texbook says it's the distillation apparatus but in other books and revision guides it says Reflux :/
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    (Original post by ioanax7)
    Can somebody tell me: Is it reflux or distillation apparatus that's used when making a ketone from a secondary alcohol? Because the texbook says it's the distillation apparatus but in other books and revision guides it says Reflux :/
    The reaction is completed under reflux normally.
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    (Original post by sophiekutie)
    I mean in terms of this type of diagram...
    Name:  image.jpg
Views: 106
Size:  384.1 KB
    Would E' + E'' = the un-catalysed activation energy ?
    (Apologies for the picture, it's a picture of my revision guide)
    Woops my bad I've never come across such a thing in my life I don't think they have to be equal, no... just the enthalpy change is the same. Though I'm not certain... I've also had a look in the George Facer book, there's nothing on that in there

    (Original post by HarryMWilliams)
    Kudos, let me know how you get on.
    You too Best of luck with revision !

    (Original post by ioanax7)
    Can somebody tell me: Is it reflux or distillation apparatus that's used when making a ketone from a secondary alcohol? Because the texbook says it's the distillation apparatus but in other books and revision guides it says Reflux :/
    Typically reflux Though I think you can use distillation apparatus, but it's a bit pointless... since the whole reason you use it with primary alcohols is so that the aldehyde does not further oxidize to carboxylic acid.

    Ketones can't be further oxidized... so you don't need to worry about having it distilled off as it's produced Reflux apparatus is therefore typically used.
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    (Original post by posthumus)
    x
    Haha that's okay, I appreciate it was an awkward question
    Thanks! And good luck! X
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    (Original post by posthumus)
    Typically reflux Though I think you can use distillation apparatus, but it's a bit pointless... since the whole reason you use it with primary alcohols is so that the aldehyde does not further oxidize to carboxylic acid.

    Ketones can't be further oxidized... so you don't need to worry about having it distilled off as it's produced Reflux apparatus is therefore typically used.
    (Original post by HarryMWilliams)
    The reaction is completed under reflux normally.
    Thank you!
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    Hello everyone can you please clear my doubt? (group 2 and 7 chapter .__.) ok so why are barium compounds the most stable group 2 compounds again? shouldn't they be the LEAST stable considering their large radius? large radius --> less attraction for the anion --> less energy needed to break apart the compound.

    HOWEVER barium compounds are in fact the MOST stable, can somebody explain to me why that is so?
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    (Original post by Kurraiyo)
    Hello everyone can you please clear my doubt? (group 2 and 7 chapter .__.) ok so why are barium compounds the most stable group 2 compounds again? shouldn't they be the LEAST stable considering their large radius? large radius --> less attraction for the anion --> less energy needed to break apart the compound.

    HOWEVER barium compounds are in fact the MOST stable, can somebody explain to me why that is so?
    Chemguide to the rescue!

    Basically the radius is larger in barium, but the overall charge is the same as it is for, say, magnesium (both will form 2+ ions). This means that the charge density is lower for barium, so it will distort the negative ions near it to a lesser extent than magnesium. The less polarised the negative ion, the more heat you need to break the bond.
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    (Original post by Kurraiyo)
    Hello everyone can you please clear my doubt? (group 2 and 7 chapter .__.) ok so why are barium compounds the most stable group 2 compounds again? shouldn't they be the LEAST stable considering their large radius? large radius --> less attraction for the anion --> less energy needed to break apart the compound.

    HOWEVER barium compounds are in fact the MOST stable, can somebody explain to me why that is so?
    I think it's something to do with the fact that the cation is bigger and therefore less able to polarise the anion. The greater the polarising ability of the cation the greater its tendency to liberate CO2 (for carbonates) and NO2 and O2 (for nitrates)

    This website explains it quite well, a bit long winded but detailed http://www.chemguide.co.uk/inorganic...mstab.html#top

    Get to the section where he starts to talk about the structure of the carbonate ion (it's the same for nitrates as well)
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    Oh okay I get it now! Thank you guys so much ^__^ !! and locked_box thank you for the link really clarified things
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    (Original post by Kurraiyo)
    Oh okay I get it now! Thank you guys so much ^__^ !! and locked_box thank you for the link really clarified things
    You're welcome Should mention that Gnome also suggested the link-but it was a little more subtley done
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    Don't know what we'd do if it wasn't for chemguide!
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    Oh I didn't know that was a link Gnome, sorry for not crediting you as well haha thanks once again! good luck for the paper
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    (Original post by posthumus)
    ah it's okay, same here I don't quite know how to feel about leaving Sixth form though At least now I don't need to call into school explaining how ill I am (so I can revise at home)

    Good luck with Biology & German I am doing nothing but unit 2/unit 4 chemistry for the next week !

    For unit 1 I think it was the worst chemistry exam I've sat yet I was expecting questions like "what is an alkane" ... and I would gain easy UMS I screwed up the reason for sodium carbonate use in cooking too believe it or not (do people use it to remove acid from their food?)... I realized afterwards it's the same thing as bicarbonate of soda Hess's law question - was unable to extract much information from their text... couldn't understand the question. The Question with Arsenic & Selenium confused me too as well as drawing cracking apparatus

    Oh well I must look forward to unit 2,4 & 5 now I quite literally need 84 UMS across all 3 of these exams.. to get my B ! This is proving so much more difficult than Physics & Maths where I need an A, and thanks to chemistry I have far less time for those 2

    & I think you'll be the boss at unit 5, hehe... best of luck with revision
    Yeah, slowly but surely becoming more and more responsible for our learning which is nice Yeah, don't worry, I didn't say bicarbonate of soda. I said use the sodium hydrogen carbonate to neutralise acids in other cooking ingredients (eg, acetic acid) which is in vinegar. Then you could use the salt from that as a seasoning. A bit long winded but it's still perfectly viable. I didnt realise it was bicarbonate of soda either, but it's slightly unfair. I think you're right though, according to Chemical principle that you actually learn. I instantly thought neutralisation reaction as they mentioned its basic properties. Yeah the Hess/Calorimetry were marks I threw away essentially XD

    You'll be alright I'm sure What are you going to study again?
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    I'm gonna do my best to do well on Unit 2.
 
 
 
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