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Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread

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Original post by ayvaak
Hey im not sure on some Unit 4 Qs. 6b ( why is there permamnent dipole dipole interactions...is it due to the polar alcohol bond) and 6c ( the wrong answer c seems feasible to me but why is that fragments without H are unlikely) 20160605_201553.jpg

Thanks in advance :smile:


I think there are permanent dipole interactions due to the C=C bond but I am not completely sure :s
Hi, does anyone know how to do combustion analysis using volumes of gases? 14651587542051743336170.jpg part c of this
Original post by samb1234
Yes that is correct. H2O <-------> OH- + H+. When you vary the temp the equil will increase/decrease the conc of oh- and h+ equally. A nice way of doing pH is to say that since conc of oh is same as h+ you can say h+ =root Kw so pH = -logrootKw


Ah okay, thank you!
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ayvaak
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Original post by sonam_28
Hi, does anyone know how to do combustion analysis using volumes of gases? 14651587542051743336170.jpg part c of this



is the answer C4H4?
Original post by ayvaak
is the answer C4H4?

Yes but how did you get that
@samb1234 When drawing repeat units for polyesters, does it matter which monomer loses just an H and which one loses OH during the formation of the ester link? So for like benzene-1,4-dicarboxylic acid and ethane-1,2-diol, when the ester link is formed, does it always have to be the alcohol losing just an H atom and the dicarboxylic acid losing the hydroxyl group?
Did a couple of U5 papers. June 2010 and June 2011 - scored 75 and 77 on 90 respectively. Decent start. Definitely plenty of awkward questions, though.
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samb1234
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Original post by Don Pedro K.
@samb1234 When drawing repeat units for polyesters, does it matter which monomer loses just an H and which one loses OH during the formation of the ester link? So for like benzene-1,4-dicarboxylic acid and ethane-1,2-diol, when the ester link is formed, does it always have to be the alcohol losing just an H atom and the dicarboxylic acid losing the hydroxyl group?


well it's not going to matter for the structure so probably not, although i suspect in the mechanism one will be favoured over the other
Original post by samb1234
well it's not going to matter for the structure so probably not, although i suspect in the mechanism one will be favoured over the other


Ah okay yeah that makes sense :smile:
I just did a paper, and was expected to know that heating the complex [Cu(H20)4(OH)2] produces the BLACK solid Copper(II)Oxide. I'll be damned if that's come up in either my CGP or Phillip Allan books, have I missed a trick or have you guys come across this?
Alright so after a day of cramming unit 5 I have gone from 38 to 57 marks which still isn't great but hopefully one more day tommorow should be enough then after that just more memorising


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Original post by lordoftheties
I just did a paper, and was expected to know that heating the complex [Cu(H20)4(OH)2] produces the BLACK solid Copper(II)Oxide. I'll be damned if that's come up in either my CGP or Phillip Allan books, have I missed a trick or have you guys come across this?


which paper was this?
Original post by Don Pedro K.
which paper was this?


January 2013 question 14a (Identitiy of B)
Original post by lordoftheties
January 2013 question 14a (Identitiy of B)


Ah yh did this one yesteday. I said CuO because it said black solid :smile:
Original post by Don Pedro K.
Ah yh did this one yesteday. I said CuO because it said black solid :smile:


Yh but how did you know its a black solid? None of my books mention this :frown: Im not worried greatly about it because there are only two solid oxides for copper and I knwo them both now thankfully, but im just worried that I never came across it...
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ayvaak
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Original post by sonam_28
Yes but how did you get that


I worked it out by trial and error until the volumes matched my the x and y values. But I'm not sure if theres a more efficient way of doing it
Original post by lordoftheties
Yh but how did you know its a black solid? None of my books mention this :frown: Im not worried greatly about it because there are only two solid oxides for copper and I knwo them both now thankfully, but im just worried that I never came across it...


I guess just prior knowledge :s!
Original post by Ayman!
Did a couple of U5 papers. June 2010 and June 2011 - scored 75 and 77 on 90 respectively. Decent start. Definitely plenty of awkward questions, though.


Cool. But are the questions too awkward? :redface:
https://c838cff4741acb48ae1ed62e59927ff4c2073557.googledrive.com/host/0B1ZiqBksUHNYbVpyRTRJN1lFS00/January%202010%20QP%20-%20Unit%204%20Edexcel%20Chemistry.pdf

In Question no 11, I got it correct but I'm confused on the fact that how does dipole moment change when the bonds stretch or bend?
Original post by sabahshahed294
https://c838cff4741acb48ae1ed62e59927ff4c2073557.googledrive.com/host/0B1ZiqBksUHNYbVpyRTRJN1lFS00/January%202010%20QP%20-%20Unit%204%20Edexcel%20Chemistry.pdf

In Question no 11, I got it correct but I'm confused on the fact that how does dipole moment change when the bonds stretch or bend?


I would think it's something to do with a shift in the electron density around the molecule; if you imagine the electron density as a 'cloud', when the molecule vibrates or the bonds stretch/bend, I'm guessing that the electron density is redistributed around a certain atom more than another, causing the change in the dipole moment?

I actually have no idea whether that's right, but that's what my reasoning would be haha.

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