Chemistry: Post your doubts here!

[fleurisabelle]

Can you explain how this is nucleophilic substitution View attachment 58706

Are you done with the whole syllabus? Actually, I've covered almost whole AS Chemistry but this question is still out of my comprehension. As far as I know, nucleophilic substitution involves halogenalkanes. Since all the halogens are more electronegative than carbon (with the exception of iodine), the electrons are pulled more by the halogens than by the carbon, which leaves the carbon a slightly positive charge while the halogen with a slightly negative charge. Now, the carbon is susceptible to attacks by nucleophiles and attaches with any nucleophile that comes in it's way. Looking at the list of common nucleophiles, NH2 is the one that could be involved here, but the picture presented by the structures show that a hydrogen has been lost, which is positive and could not possibly have acted as a nucleophile! if you do understand, be kind enough to explain me too!

 

[The Sarcastic Retard]

Can you explain how this is nucleophilic substitution View attachment 58706

N has lonepair to donate, so this reaction can be NS. That's all.
Reagent with lone pair can attack that's what we learnt right?

 

[fleurisabelle]

How can I know by just looking at the skeletal formula whether it contains a CH group a CH2 or a CH3, like there in the image, if I've gotta write it's structural formula, what it's going to be? I know that one projecting above must be a CH3 but what about the other four?

 

[fleurisabelle]

N has lonepair to donate, so this reaction can be NS. That's all.
Reagent with lone pair can attack that's what we learnt right?

Do you mean to say that it's the acid that has gone under nucleophilic substitution? but aren't those bromoethanes that go into nucleophilic substitution?

 

[nehaoscar]

How can I know by just looking at the skeletal formula whether it contains a CH group a CH2 or a CH3, View attachment 58729 like there in the image, if I've gotta write it's structural formula, what it's going to be? I know that one projecting above must be a CH3 but what about the other four?

Remember this for skeletal formula
Where each line joins, there is a C
The C must have 4 bonds and if no other functional groups are shown on the diagram, then it will be bonded to H
In this example, i have shown you what if would be like if there was OH
Note: It's better to convert it to displayed first and then to structural until you are confident with the skeletal formula.

 

[fleurisabelle]

Remember this for skeletal formula
Where each line joins, there is a C
The C must have 4 bonds and if no other functional groups are shown on the diagram, then it will be bonded to H
In this example, i have shown you what if would be like if there was OH
Note: It's better to convert it to displayed first and then to structural until you are confident with the skeletal formula.
View attachment 58730

thank you...it pretty much explained

 

[Catherine_1]

Hey can anyone please help me with this graph-:


This is the marking scheme


9701_s12_qp_51

Thank you!

 

[AnonymousX9]

Can anyone please explain the VSEPR (valence shell electron pair repulsion) theory that we are supposed to know for chapter 3 (chemical bonding) in AS Chem? Also, I do not understand the rules. I mean, if a rule states that if there are 4 pairs of electrons (no lone pairs) around the central atom then the molecule is said to be tetrahedral with a bond angle of 109.5 degrees, however, that is not the case with a CO2 molecule which I don't seem to get as to why it is linear and not tetrahedral even though it has 4 pairs of electrons around the Carbon atom. If anyone could explain or direct me to a link online which explains it clearly with all the rules that we are supposed to know to determine the shape that would be really helpful.

Thanks.

 

[Eugene99]

Can anyone please explain the VSEPR (valence shell electron pair repulsion) theory that we are supposed to know for chapter 3 (chemical bonding) in AS Chem? Also, I do not understand the rules. I mean, if a rule states that if there are 4 pairs of electrons (no lone pairs) around the central atom then the molecule is said to be tetrahedral with a bond angle of 109.5 degrees, however, that is not the case with a CO2 molecule which I don't seem to get as to why it is linear and not tetrahedral even though it has 4 pairs of electrons around the Carbon atom. If anyone could explain or direct me to a link online which explains it clearly with all the rules that we are supposed to know to determine the shape that would be really helpful.

Thanks.

Why don't you try Khanacademy's lectures. They are interesting and explains you everything. For the VSEPR Theory check this one: https://www.khanacademy.org/science...-dot-structures/v/vsepr-for-3-electron-clouds

 

[Myaaa_20]

Does anyone know where I can get Paper 1 questions topic-wise?

 

[The Sarcastic Retard]

Does anyone know where I can get Paper 1 questions topic-wise?

Chemistry Paper 1 topical past papers

 

[FranticAmaze]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s03_qp_4.pdf
qs 2b(ii) pls explain

 

[Youknowwhoo]

can anyone tell me how to do rough work in P1 is it permissible?
please

 

[Youknowwhoo]

can anyone tell me how to do rough work in P1 is it permissible?
please

 

[nehaoscar]

can anyone tell me how to do rough work in P1 is it permissible?
please

Yep.. just do it on the side of the question (but within the margin) or ask for a supplement which later needs to be attached with your paper
If you do it on a supplement make sure you label this as rough work and write the question number cause sometimes marks may be awarded based on your workings

 

[Youknowwhoo]

Yep.. just do it on the side of the question (but within the margin) or ask for a supplement which later needs to be attached with your paper
If you do it on a supplement make sure you label this as rough work and write the question number cause sometimes marks may be awarded based on your workings

hey thx so much neha, ive sat previously in cie exams are u sure about this supplement paper ? i never saw anyone take it btw dude because i think most people do it on the P1 itself haha ???

 

[fleurisabelle]

can anyone tell me how to do rough work in P1 is it permissible?
please

I don't think they would have any problem if you do the rough work on the paper itself. They shouldn't actually have any problem! The question paper is our property as long as it is in our hands ain't it? (though you should make sure you don't write in the space left for examiner)

 

[nehaoscar]

hey thx so much neha, ive sat previously in cie exams are u sure about this supplement paper ? i never saw anyone take it btw dude because i think most people do it on the P1 itself haha ???

Yeah most do it in the blank space available But my teacher had said that if required you can take rough paper so yeah
But i guess it's better to do it on the question paper in P1 since it's mcq and they don't need to see any working - either you answer it right or wrong

 

[Catherine_1]

How to prepare for paper 5?Any good sites?

 

[Youknowwhoo]

Yeah most do it in the blank space available But my teacher had said that if required you can take rough paper so yeah
But i guess it's better to do it on the question paper in P1 since it's mcq and they don't need to see any working - either you answer it right or wrong

lol well 1 hour 40 questions is the biggest joke ever told in the history of mankind ,how do you answer something like calculations, i read somewhere to devote 1 minute to a question
lol