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Chemistry unit 6 June 2016

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Original post by Adorable98

Why is this the answer:
It contains a phenol group/has OH attachedto benzene ring.

I wrote x contains a Cl- :frown:


This falls in the reactions of phenols in Unit 5 chapter 3. You have to know that reaction and what happens so one of them is formation of white ppt and decolorisation of bromine.
(edited 7 years ago)
Original post by baebae
guys what do we need to know about chromatography for unit 6 ? :redface:o


Yup. There was a 4 mark explanation on chromatography.
Original post by Adorable98

Why is this the answer:
It contains a phenol group/has OH attachedto benzene ring.

I wrote x contains a Cl- :frown:


Phenol reacts with bromine to form HBr and white precipitate of 2,4,6-tribromophenol
Therefore, the benzene ring contains a phenol group.
(edited 7 years ago)
Original post by Ayman!
Sabah, please look at this video if you know where the formula comes from - https://youtu.be/c9uJ42_7DEI

You don't need to know this for the course but it does help you understand WHY the volume is proportional to the concentration rather than it just is.



Oh I liked all the IAL Jan papers! May 15 was my most hated one. Yuck.


Yeah, May 2015 was so dull, I almost fell asleep while solving it!!!
Reply 164
Avatar for baebae
baebae
7
Original post by sabahshahed294
Yup. There was a 4 mark explanation on chromatography.

was it about gas chromatography or hplc? :/
Original post by Adorable98

Why is this the answer:
It contains a phenol group/has OH attachedto benzene ring.

I wrote x contains a Cl- :frown:


Bromine water is decolourised by two compounds only:

Phenol - A white ppt is formed that is 2.4.6-tribromophenol
Alkene - Colour change from yellow to colourless
Original post by baebae
was it about gas chromatography or hplc? :/


No, it was just the basic chromatography.
Original post by baebae
was it about gas chromatography or hplc? :/


It was about Thin layer chromotography
Hey, does anyone know why the white solid formed is CuCl, this is from January 2016 where the cation was Cu2+ and the anion was Cl- ?
b.JPG32.0KB
Reply 169
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baebae
7
oh okay thanks guys :biggrin:
Original post by PlayerBB
It was about Thin layer chromotography


Thin layer? Wasn't it the basic one?
Original post by sabahshahed294
This falls in the reactions of phenols in Unit 5 chapter 3. You have to know that reaction and what happens so one of them is formation of white ppt and decolorisation of bromine.


Original post by Mehodax
Phenol reacts with bromine to form HBr and white precipitate of 2,4,6-tribromophenol
Therefore, the benzene ring contains a phenol group.


Original post by PlayerBB
Bromine water is decolourised by two compounds only:

Phenol - A white ppt is formed that is 2.4.6-tribromophenol
Alkene - Colour change from yellow to colourless


Thank you!!!! :biggrin:
Reply 172
Avatar for baebae
baebae
7
Original post by PlayerBB
Hey, does anyone know why the white solid formed is CuCl, this is from January 2016 where the cation was Cu2+ and the anion was Cl- ?


i think by saying that a colorless solution forms they meant that Cu ion in the solid will be Cu+ because it has full d subshell? and hence CuCl and not CuCl2 but i might be well wrong
Original post by Adorable98

Why is this the answer:
It contains a phenol group/has OH attachedto benzene ring.

I wrote x contains a Cl- :frown:


We know that the compound contains a benzene ring. If we try and react benzene with bromine water, we will get no reaction as the electron density of the benzene ring is not high enough to form the required Br+ electrophile, so if you wanted to brominate benzene you would need to generate Br+ in another way. In comparison, in phenol the lone pairs of the oxygen are partially delocalised into the ring system giving it a much higher electron density, such that it can polarise the Br-Br bond sufficiently for an electrophilic substitution reaction to occur. After one bromine has added, it is possible for another 2 to substitute onto the ring, and for reasons you don't need to know they will always be in position 2,4,6 so you get 2,4,6-tribromophenol (or a variant of this) which is a white precipitate
Original post by PlayerBB
Hey, does anyone know why the white solid formed is CuCl, this is from January 2016 where the cation was Cu2+ and the anion was Cl- ?


white solid, hence copper must have full d orbitals as otherwise there would be slight energy differences between the d orbitals which means that when electrons transfer between them they emit photons when they drop back down in energy
Original post by sabahshahed294
Thin layer? Wasn't it the basic one?


Depends, what do you exactly mean by basic one ?
Original post by baebae
i think by saying that a colorless solution forms they meant that Cu ion in the solid will be Cu+ because it has full d subshell? and hence CuCl and not CuCl2 but i might be well wrong


Original post by samb1234
white solid, hence copper must have full d orbitals as otherwise there would be slight energy differences between the d orbitals which means that when electrons transfer between them they emit photons when they drop back down in energy


Thank you guys so much, I have been stuck on this for ages and it didn't cross in my mind that it would be related to full 3d sub-shell

What does everyone think about Q.3 January 2016, was it SO HORRIBLE or is it just me ?
Reply 177
Avatar for baebae
baebae
7
the whole paper was horrible in my opinion xD
Original post by PlayerBB
Thank you guys so much, I have been stuck on this for ages and it didn't cross in my mind that it would be related to full 3d sub-shell

What does everyone think about Q.3 January 2016, was it SO HORRIBLE or is it just me ?
Reply 178
Avatar for baebae
baebae
7
do you guys think equilibria can come up?
Original post by baebae
the whole paper was horrible in my opinion xD


Q.3 and Q.2 were kinda nice but the rest made feel so demotivated!!

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