Chemistry: Post your doubts here!

[periyasamy]

Hi guys,need some help here.
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_41.pdf
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_ms_41.pdf
Q8(a) n d(11)
Thank u a lot

 

[periyasamy]

I ll rephrase it

What is the compound R'CONH2 called?
And as u said there is a reaction RCOCl+R'NH2 and product is R'CONH2 the R here is the R of R'NH2 so where did the R for RCOCl go?

The rcocl reaction with rnh2,,,,iS SUCH THAT the rcocl act as an acid(rcooh)...The product will actually belike ester,----->RCONH2R'..

 

[A star]

Hi guys,need some help here.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_41.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_ms_41.pdf
Q8(a) n d(11)
Thank u a lot

well basically the no of sidechains effect the packing of the layers of the polymer, closer the layers are in Poly(ethene) the more effective the packing becomes due to vanderwalls forces. So they just wanted you to show efficent packing in HDPE with no or lesser ammount of sidechains and distorted packing in the LDPE.
now for d(ii)
well for any object to conduct electricity it ust have a sea of delocalised electrons or in the case of polymers their p-orbitals must overlap in order to transfer e-s from one end to another and must be planer. I am still unsure about being planer or not :/

 

[Namehere]

Hi guys,need some help here.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_41.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_ms_41.pdf
Q8(a) n d(11)
Thank u a lot

Q8(a) - For the diagram you are supposed to show that LDPE has a lot of side chains and because of this the straight chains can´t pack together as closely - you can see it as if there were "waisted space", so because of the branching there is more "empty" space between the chains and hence LDPE is lower in density. HDPE is just the reverse arguments, with many fewer side chains and the staight chains can pack much more closely together so that all the polymer is contained in a smaller space, hence the higher density.

Q8(dii) - I´m not sure if I´m right so if im wrong please do someone correct me. The molecule will need to be planar. Main reason is that if you have another molecule at the top or at the bottom, for the electrons to "jump" up or down (i.e. conduct) the pi bonds of the above/bottom molecule would need to overlap with the "middle" molecule, and for them to overlap, they have to lie in the same plane, hence why it would need to be planar.

Hope it helps.

 

[periyasamy]

well basically the no of sidechains effect the packing of the layers of the polymer, closer the layers are in Poly(ethene) the more effective the packing becomes due to vanderwalls forces. So they just wanted you to show efficent packing in HDPE with no or lesser ammount of sidechains and distorted packing in the LDPE.
now for d(ii)
well for any object to conduct electricity it ust have a sea of delocalised electrons or in the case of polymers their p-orbitals must overlap in order to transfer e-s from one end to another and must be planer. I am still unsure about being planer or not :/

thanks buddy!!!

 

[periyasamy]

Q8(a) - For the diagram you are supposed to show that LDPE has a lot of side chains and because of this the straight chains can´t pack together as closely - you can see it as if there were "waisted space", so because of the branching there is more "empty" space between the chains and hence LDPE is lower in density. HDPE is just the reverse arguments, with many fewer side chains and the staight chains can pack much more closely together so that all the polymer is contained in a smaller space, hence the higher density.

Q8(dii) - I´m not sure if I´m right so if im wrong please do someone correct me. The molecule will need to be planar. Main reason is that if you have another molecule at the top or at the bottom, for the electrons to "jump" up or down (i.e. conduct) the pi bonds of the above/bottom molecule would need to overlap with the "middle" molecule, and for them to overlap, they have to lie in the same plane, hence why it would need to be planar.

Hope it helps.

Thanks buddy!!!

 

[chocolate_girl]

The rcocl reaction with rnh2,,,,iS SUCH THAT the rcocl act as an acid(rcooh)...The product will actually belike ester,----->RCONH2R'..

But this way wont nitrogen bond with four atoms

 

[A star]

But this way wont nitrogen bond with four atoms

yes nitrogen can bond with four atoms if the fourth is a dative bond and i guess that compound is a amide

 

[daredevil]

I ll rephrase it

What is the compound R'CONH2 called?
And as u said there is a reaction RCOCl+R'NH2 and product is R'CONH2 the R here is the R of R'NH2 so where did the R for RCOCl go?

Ummm there was an error in that equationn....


RCOCl + R'NH2 --> RCONHR' + HCl

 

[chocolate_girl]

1. understand, in simple terms, the concept of electronegativity
   and apply it to explain the properties of molecules such as bond polarity (3h), the dipole moments of molecules (3j), the behaviour of oxides with water (3.1j) and the acidities of chlorine-substituted ethanoic acids (10.6c)
   
   Please explain me the last chlorine substituted ethanoic acid part

 

[chocolate_girl]

yes nitrogen can bond with four atoms if the fourth is a dative bond and i guess that compound is a amide

Thankyou im really greatful

 

[chocolate_girl]

Ummm there was an error in that equationn....


RCOCl + R'NH2 --> RCONHR' + HCl

Thanks for ur time

 

[asd]

Question explaination needed :-/

I didnt get how they calculated it

Umm did you get your answer yet?
well, not in a mood to go through all those 8 pages.
Khair, look how theyre changing the concentrations of the reactants, and how the initial rate of the reaction changes. Work them out in fractions; change in conc of reactant A= 1.6/1.1= 1.45 which equals the change in initial rate, 2.3/1.6. Apparently, changing the concentration of reactant B has no effect on the rate, since all the effect is only coming from the reactant A alone. So, change in reactant A is proportional to change in initial rate. therefore, first order with respect to reactant A, and 0 w.r.t B.

 

[asd]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_42.pdf

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_ms_42.pdf

Q 3 c... y is another compound made?? is it like instead of C a cmpound D is made or what??

Both compounds are being formed at the same time. And no, D is not being made in place of C. However, in my opinion C is the preferential product of the reaction since production of D has a relatively longer route.
And for why D is being made, compound B dissociates in the aq solution giving the organic anion, and the Na+ cation. The negative charge on the Oxygen atom travels to the Oxygen atom at the bottom (Double bond b/w 2 carbon atoms on the right side of the molecule acts a bridge in extending the pi-bonding system). Oxygen at the bottom now acts a nucleophile and attacks on the positive Carbon atom on the enthanoyl chloride. Another possibility in my opinion could be that the electrons travel to the oxygen at the top and this could be another potential nucleophile allowing CH3CO+ to attach to this oxygen.

 

[Hassan Ali Abid]

Who has an idea of the likely practical questions in paper 3 for 2014

Which variant ???

 

[NinjaInPyjamas]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_22.pdf

q3 please help!
I have difficulty deriving the formula...is there a way to understand easier?

Thanks in advance!

 

[Hassan Ali Abid]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_22.pdf

q3 please help!
I have difficulty deriving the formula...is there a way to understand easier?

Thanks in advance!

The simplest way is to open the given structure so that u can have a better of idea and then u can use ur knowledge+ understanding to solve such type of questions ...
eg in this question when u open the given compound u can see there are 2 acid groups and one alcohol group ...
to make the structure of A ..u have to recall the reaction of alcohol with acid ....simply 2 ester linkage will be formed in this ..
for making B u see now the alcohol group in compound will react ethanoic acid ..
For making C ...remove the water ( by removing OH and H ) and alkene will form ..
In E...its the reaction with water so again add water in it ....
For F ...its a cold dil reaction of alkene so 2 -OH groups will be added in it ..
In D...as its a reaction with hot .conc. so two products will be formed in it .
If u still didnt get it then i'll draw the structures of all these..okay ..

 

[NinjaInPyjamas]

The simplest way is to open the given structure so that u can have a better of idea and then u can use ur knowledge+ understanding to solve such type of questions ...
eg in this question when u open the given compound u can see there are 2 acid groups and one alcohol group ...
to make the structure of A ..u have to recall the reaction of alcohol with acid ....simply 2 ester linkage will be formed in this ..
for making B u see now the alcohol group in compound will react ethanoic acid ..
For making C ...remove the water ( by removing OH and H ) and alkene will form ..
In E...its the reaction with water so again add water in it ....
For F ...its a cold dil reaction of alkene so 2 -OH groups will be added in it ..
In D...as its a reaction with hot .conc. so two products will be formed in it .
If u still didnt get it then i'll draw the structures of all these..okay ..

thank you so much that was soo helpful! if you don't mind can you please draw organic chemistry is difficult for me
also can you please help with (b) and (d) please
thaanxxx

 

[Hassan Ali Abid]

thank you so much that was soo helpful! if you don't mind can you please draw organic chemistry is difficult for me
also can you please help with (b) and (d) please
thaanxxx

 

[Hassan Ali Abid]

NinjaInPyjamas