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Chemistry Unit 6B [6CH08][Edexcel][International Candidates][22.05.2012]

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Original post by solittletime
Also, why is CuI colourless?


Cu+ has an electronic configuration of [Ar]4s2 3d10, with a full 3d subshell, it is not a transition metal, so its ppt should be white.
Original post by Yorrap


for Q4, i said conc H2SO4+conc HNO3 added to make NO2+ to attack the "whatever compound i forgot" for nitration.

the molar mass of the product = 136 -1 +14+16x2 = 181
and the percentage yield is 51.1%

why using solvent 1 will have a lower yield than using solvent 2?
i wrote because the difference in the solubility at 10degree and 70degree for solvent 1 is less than that of solvent 2, so less product formed crystals at 10 degree and hence lower yield.

yield of crystals when using 50g of solvent 2: 9.5/2 - 2.0/2 = 3.75g

hmm btw, spray with ninhydrin is for amino acids :P
(edited 11 years ago)
Reply 182
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Yorrap
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Original post by sasha_olemui
for Q4, i said conc H2SO4+conc HNO3 added to make NO2+ to attack the "whatever compound i forgot" for nitration.

the molar mass of the product = 136 -1 +14+16x2 = 181
and the percentage yield is 51.1%

why using solvent 1 will have a lower yield than using solvent 2?
i wrote because the difference in the solubility at 10degree and 70degree for solvent 1 is less than that of solvent 2, so less product formed crystals at 10 degree and hence lower yield.

yield of crystals when using 50g of solvent 2: 9.5/2 - 2.0/2 = 3.75g

hmm btw, spray with ninhydrin is for amino acids :P


rofl i know xD
I had no idea what to do so, I wrote that :P
Reply 183
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Yorrap
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2
Original post by sasha_olemui
for Q4, i said conc H2SO4+conc HNO3 added to make NO2+ to attack the "whatever compound i forgot" for nitration.

the molar mass of the product = 136 -1 +14+16x2 = 181
and the percentage yield is 51.1%

why using solvent 1 will have a lower yield than using solvent 2?
i wrote because the difference in the solubility at 10degree and 70degree for solvent 1 is less than that of solvent 2, so less product formed crystals at 10 degree and hence lower yield.

yield of crystals when using 50g of solvent 2: 9.5/2 - 2.0/2 = 3.75g

hmm btw, spray with ninhydrin is for amino acids :P


ah thanks for reminding that question.

I also got 18x for molar mass (can't remember exact value) I did subtract one or 2 hydrogens from the benzene ring depending on how many groups were attached on the ring -i can't remember now

but i remember 1 hydrogen was missing in the benzene ring so
(12x6) + (5x1) = 77 for C6H5
NO2 = 46
so 58 left. was the remaining group CH2OOC ?

join live chat!
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(edited 11 years ago)
For the improvement for the chromatography question, I wrote place a drop of methyl 2-nitrobenzene and a drop of methyl 3-nitrobenzene along with the drop of the ethanol solution, then run the chromatogram and compare the distances the drops travelled.
Was it a ketone or an aldehyde =S
Original post by Yorrap
ah thanks for reminding that question.

I also got 18x for molar mass (can't remember exact value) I did subtract one or 2 hydrogens from the benzene ring depending on how many groups were attached on the ring -i can't remember now

but i remember 1 hydrogen was missing in the benzene ring so
(12x6) + (5x1) = 77 for C6H5
NO2 = 46
so 58 left. was the remaining group CH2OOC ?

join live chat!
http://edexcelchemistrl6b.chatango.com/


there's no need for calculating the molar mass starting from the very beginning :P the molar mass of the compound before nitration is given in the question as 136! so u just need to subtract one hydrogen out and add the molar mass of NO2 to it
Original post by xstrawberryswingx
Was it a ketone or an aldehyde =S


ROARRR i even wrote it as an acid :frown: -COOH :frown:((((
shoot i just added the molar mass of NO2 to it x_x Aciid?! But didnt the tests below give it away DNP and Tollens reagent =P
Original post by xstrawberryswingx
shoot i just added the molar mass of NO2 to it x_x Aciid?! But didnt the tests below give it away DNP and Tollens reagent =P


well yeah..seems like the answer is ketone?? i dunno :frown:(
but if u wrote ketone, u scored 2 from the DNP and Tollen's reagent.
aldehyde, scored 1
acid, scored 2 (hell yeah :colondollar: )
Reply 190
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Original post by sasha_olemui
there's no need for calculating the molar mass starting from the very beginning :P the molar mass of the compound before nitration is given in the question as 136! so u just need to subtract one hydrogen out and add the molar mass of NO2 to it


lol seems like i wasted a few seconds to calculate it then xD

Oxidation of Cyclohexanol to Cyclohexanone
http://adf.ly/8qjJD
(edited 11 years ago)
Reply 191
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laugh123
Shoot!! I considered it as an aldehyde!! How many points overall was that ?
Reply 192
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iesians
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i found the wrong molar mass of the compound in end !! F*^*(&%&^$&$!!

wrong chromatography !
for sulphuric acid i wrote it acts as a catalyst !
without saying that it produces electrophile !!!
OK IM DEAD !!!!
Wasnt it an aldehyde?? How was it an acid??? :confused:
Reply 194
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iesians
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Original post by sasha_olemui
Cu+ has an electronic configuration of [Ar]4s2 3d10, with a full 3d subshell, it is not a transition metal, so its ppt should be white.


you wrote the worng cinfiguration but explanation is right ! configuration is [Ar]3d10 !! theres no electron in 4s subshell !!
Reply 195
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Original post by totally lost
Wasnt it an aldehyde?? How was it an acid??? :confused:


Neither of them are correct ! it was actually a ketone ! bcz CYCLOHEXANOL is a SECONDARY ALCOHOL ! and on oxidation it only produces a ketone !chk this out :-


http://wwwchem.uwimona.edu.jm/lab_manuals/c10expt21.html
(edited 11 years ago)
Reply 196
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aqua05
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how did you guys find the paper???

I messed it up :frown: :frown: im so scared!!!! errrr
Reply 197
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iesians
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Original post by aqua05
how did you guys find the paper???

I messed it up :frown: :frown: im so scared!!!! errrr


AQUAAAA !!!! :frown: i wrote sulphuric acid acts as a catalyst !!!!

and i wrtoe 246 tribromophenol is orange !!! (when it actually is white) !!!

for drop wise ammonia ! i wrote ion formed is cr(OH)3(H2O)3 !!! is tht right ..?!?
Original post by iesians
Neither of them are correct ! it was actually a ketone ! bcz CYCLOHEXANOL is a SECONDARY ALCOHOL ! and on oxidation it only produces a ketone !chk this out :-


http://wwwchem.uwimona.edu.jm/lab_manuals/c10expt21.html

Ahhh! Am doomed!! This means that even my structural formula and tollens reagents ansa was wrong:frown: I screwd up on the chromotography qstn as well
Reply 199
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iesians
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Original post by sasha_olemui
for Q4, i said conc H2SO4+conc HNO3 added to make NO2+ to attack the "whatever compound i forgot" for nitration.

the molar mass of the product = 136 -1 +14+16x2 = 181
and the percentage yield is 51.1%

why using solvent 1 will have a lower yield than using solvent 2?
i wrote because the difference in the solubility at 10degree and 70degree for solvent 1 is less than that of solvent 2, so less product formed crystals at 10 degree and hence lower yield.

yield of crystals when using 50g of solvent 2: 9.5/2 - 2.0/2 = 3.75g

hmm btw, spray with ninhydrin is for amino acids :P


to improve chromatography !
i wrote run the chromatogram again by turning 90 degrees clockwise !! i read it in the students book so i just wrote it !! :tongue:

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