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Chemistry: Post your doubts here!

Catherine_1

Catherine_1

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Hey can anyone please help me with this graph-:
upload_2016-1-5_17-29-40.png

This is the marking scheme

upload_2016-1-5_17-30-15.png
9701_s12_qp_51

Thank you!:)
 
A

AnonymousX9

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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

Eugene99

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AnonymousX9 said:
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.
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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
 
nehaoscar

nehaoscar

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

Youknowwhoo

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nehaoscar said:
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
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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 ???
 
F

fleurisabelle

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Youknowwhoo said:
can anyone tell me how to do rough work in P1 is it permissible?
please
Click to expand...
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 :D ain't it? (though you should make sure you don't write in the space left for examiner)
 
nehaoscar

nehaoscar

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Youknowwhoo said:
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 ???
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Yeah most do it in the blank space available :p But my teacher had said that if required you can take rough paper so yeah :p
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 :p :D
 
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Youknowwhoo

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nehaoscar said:
Yeah most do it in the blank space available :p But my teacher had said that if required you can take rough paper so yeah :p
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 :p :D
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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
 
nehaoscar

nehaoscar

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Youknowwhoo said:
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
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Yeah they say 1min per question is ideal but i never used that logic because that just created more tension for me!
Instead don't focus on the time for each question and just leave the questions that you can't do for the last
Do all the ones you can first
For the calculation question if you think you know it attempt it, but then if it's taking too long and if you think it's wrong then leave it for the time being and come back to it later (Star these question so you know which ones to go back to)
 
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