Chemistry: Post your doubts here!

[iKhaled]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_2.pdf
Variant 1, Q.4 a the last box when you add k2Cr2O7/H+. Also b)ii)
also Q.5. a)

question 4 a) last box u have CH2(OH)CH(OH)CO2H u have a hydroxyl group attached to a carbon which is attached to one neighboring carbon and a hydroxyl group attached to a carbon which is attached to 2 neighboring carbons so a primary and a secondary alcohol present so when oxidation takes place the primary side will be a carboxylic acid which is this one CH2(OH)-R will be CO2H-R and this one CH(OH)CO2H is a secondary alcohol so will oxidise to a ketone and will be R-COCO2H add them together and u will get the organic compound HO2COCO2H

5a u have 2 similar ketones CH3-C=O(CH3) that will be added to each other, one ketone will donate its H from a methyl group to the C=O of the other ketone and attach to each other..its really difficult to explain this one here but if u dont get the idea tell me....

 

[daredevil]

hmm well i knew it from the beggining

yeah and that makes u the dude ryt?!! *applause* u win

 

[daredevil]

okay guys QUESTIONS!! :O
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_2.pdf

Q 1b and d -__- *yelps* hellp :/

 

[daredevil]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s09_qp_2.pdf
variant 2
Q1c

 

[PhyZac]

okay guys QUESTIONS!! :O
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_2.pdf

Q 1b and d -__- *yelps* hellp :/

for (b)
ethanal, u know C=O (C double bond O) therefore, permanent dipole.(and C is partially +ve)
ethanol hydrogen bond because there are both H partially +ve and O partially -ve
methoxy... same as ethanal, partially -ve O , so permanent dipole (and C is partially +ve)
propane, no highly electronegative atom thus, temporary or induced dipoles, (Van Der Waals!)


EDIT: for (d), hydrogen bonds exist between water, but no between ethoxy since it doesnt have partially +ve H.

 

[PhyZac]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_2.pdf
variant 2
Q1c

CuCl2 is more exothermic and thus more stable.

[I checked mark scheme it said chlorine is powerful oxidizing agent]
^hmm, i dont know why!
(littlecloud11 or anyone please)

 

[Abu mota]

question 4 a) last box u have CH2(OH)CH(OH)CO2H u have a hydroxyl group attached to a carbon which is attached to one neighboring carbon and a hydroxyl group attached to a carbon which is attached to 2 neighboring carbons so a primary and a secondary alcohol present so when oxidation takes place the primary side will be a carboxylic acid which is this one CH2(OH)-R will be CO2H-R and this one CH(OH)CO2H is a secondary alcohol so will oxidise to a ketone and will be R-COCO2H add them together and u will get the organic compound HO2COCO2H

5a u have 2 similar ketones CH3-C=O(CH3) that will be added to each other, one ketone will donate its H from a methyl group to the C=O of the other ketone and attach to each other..its really difficult to explain this one here but if u dont get the idea tell me....

I don't understand 5a still.

 

[littlecloud11]

CuCl2 is more exothermic and thus more stable.

[I checked mark scheme it said chlorine is powerful oxidizing agent]
^hmm, i dont know why!
(littlecloud11 or anyone please)

CuCl2 is more stable than CuCl, that's correct but I think the question wanted a more specific answer. For example if you reacted copper with a weak oxidizing agent, bromine for example, you would end up with a mixture of CuCl and CuCl2 because even though CuCl2 is more stable Br2 didn't have the power to oxidize all the Cu atoms to Cu2+ ions. So, you can infer that the reason only CuCl2 is produced when it reacts with Cl is because it has strong oxidizing powers.

 

[iKhaled]

I don't understand 5a still.

here is the best i can do, in order for u to understand it..
one of the methyl groups on the ketones will donate an H to the c=o of the other ketone and this will break the c=o bond forming a C-OH bond and the rest of that molecule will attach to the other ketone from the part where the CH3 donated the H..here in the drawing u might get it ( excuse my shity drawings but i am using touch pad thats y)

 

[Abu mota]

here is the best i can do, in order for u to understand it..
one of the methyl groups on the ketones will donate an H to the c=o of the other ketone and this will break the c=o bond forming a C-OH bond and the rest of that molecule will attach to the other ketone from the part where the CH3 donated the H..here in the drawing u might get it ( excuse my shity drawings but i am using touch pad thats y)

ty, but how am i supposed to know that? Is this like a known reaction or do we interpret it from how compound G looked like?

 

[iKhaled]

ty, but how am i supposed to know that? Is this like a known reaction or do we interpret it from how compound G looked like?

it is "kind of" a known reaction, specially with aldehyde when u get 2 identical ketones or aldehydes and the question says the compound formed contains an OH group then use it as a hint that these 2 ketones or aldehydes will attach

 

[PhyZac]

CuCl2 is more stable than CuCl, that's correct but I think the question wanted a more specific answer. For example if you reacted copper with a weak oxidizing agent, bromine for example, you would end up with a mixture of CuCl and CuCl2 because even though CuCl2 is more stable Br2 didn't have the power to oxidize all the Cu atoms to Cu2+ ions. So, you can infer that the reason only CuCl2 is produced when it reacts with Cl is because it has strong oxidizing powers.

Thank you soooo much!! I totally forgot that in CuCl (Cu has +1) and CuCl2 (Cu has 2+). Jazaki Allah khairan, and yes now I understand the answer. Thanks alot!!
May Allah S.W.T make your and your families lives happy and blessed with success, Aameeen!!!! Thanks aloooot!

 

[daredevil]

CuCl2 is more exothermic and thus more stable.

[I checked mark scheme it said chlorine is powerful oxidizing agent]
^hmm, i dont know why!
(littlecloud11 or anyone please)

oooh Holy ...!!! I cud've racked up my brain for HOURS and never would've gotten to the point that Cl2 being a strong oxidising agent is the thing here!! littlecloud11 thanks a bunch man!!

 

[knowitall10]

Assalamu alaykum!
Can someone please tell me what "re-heat to constant mass" might mean?
I'm asking regarding the second point of Q1(e) in the P5 mark scheme of o/n 2012-v1.
Thanks a lot!

 

[PANDA-]

Assalamu alaykum!
Can someone please tell me what "re-heat to constant mass" might mean?
I'm asking regarding the second point of Q1(e) in the P5 mark scheme of o/n 2012-v1.
Thanks a lot!

You heat the sample, and decomposition will happen, reducing the mass, you let it cool, measure the weight, heat again, let it cool, measure the weight... and repeat the process until the mass no longer changes from one heat to another. This is based on what I know from AS practical paper 3.

 

[knowitall10]

Alright, thanks a lot! Jazak Allahu Khair!
I wrote that answer down, so how should i mark it? i mean, how many marks do i get to write that? Just one?

 

[PANDA-]

Alright, thanks a lot! Jazak Allahu Khair!
I wrote that answer down, so how should i mark it? i mean, how many marks do i get to write that? Just one?

I don't really know. I'm an AS student, so I know this from my paper 3 practical (not alt. to practical), so I just do this in the lab.

 

[knowitall10]

Oh oh ok, I'm sorry, but thanks a lot for answering my question!

 

[PANDA-]

Oh oh ok, I'm sorry, but thanks a lot for answering my question!

No problem. May Allah grant you success, and myself as well. In Shaa Allah

 

[A star]

what in the worls fajans rule?is itin As? few A2 friends saying it is in As