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AS Chemistry- helping each other out!

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Original post by Coerce
No the answer is -672 kJ mol^-1 I'll message you a picture of i can plug my phone into laptop two seconds


Well then the mass that was used was 200grams not 100 grams!
Original post by Dylann
Well then the mass that was used was 200grams not 100 grams!


I'll send you imgs in a sec - can you jus run through it then with numericals exam tommorow and the maths part of chapter 7 is confusing me to death! :frown: - I take AS maths too wow
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kira1
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Original post by cerlohee
I got a D in my mocks and 90% im my final exams. It's defo possible, as long as you put the work in and learn from your mistakes (examiner reports are good for this)
PM if you want actual advice haha. :smile:

Edit: my teacher also told me that I wouldn't get above a C in Chen. Belieeeeeve in yourself and work hard you'll be fine 😎
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Woman you are a life saver, thank you so much
I'm so grateful and I'm sorry to say if you were with me right now I'd give you a bone crushing hug
Thank you
Reply 743
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Naga7o
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Original post by Coerce
I'll send you imgs in a sec - can you jus run through it then with numericals exam tommorow and the maths part of chapter 7 is confusing me to death! :frown: - I take AS maths too wow


Can you send me a picture of it as well?

Thanks
Hey got a qualitative isa tomorrow and our teacher wasn't very specific :/ Heres the list :mad:: OBSERVATIONS AND BALANCED SYMBOL EQUATIONS.
You need to go through reactions and equations off:
Metal Carbonates + acids
Metal Carbonates heated
Metal oxides + acids
Precipitation reactions and the ionic equations for them.
Displacement reaction and change of oxidation number.

Help plz
Original post by kira1
So I just had a mock exam and got an E, at the end of this year I need a high A, is that possible? If so how ? I feel so stressed and keep imagining myself failing. God forbid


Of course. I got a U in my first chemistry test and now I'm averaging As. Just gotta understand the content, go over it regularly and do past papers. I usually watch YouTube videos on the topics I find difficult and that helps.

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Where about's is everyone content wise? My teacher is panicking about finishing.
Original post by BIOCH3M
Where about's is everyone content wise? My teacher is panicking about finishing.

on AQA have done about 3/11 topic in unit 2. But it's the big topics with the mechanism and stuff the other chapters shouldn't take long. But I am guessing we are fairly behind where we should be at.
Original post by Super199
on AQA have done about 3/11 topic in unit 2. But it's the big topics with the mechanism and stuff the other chapters shouldn't take long. But I am guessing we are fairly behind where we should be at.


I'm not on AQA and luckily as it seems a bit harder than OCR. We still have a quarter left and no controlled assessments completed either!
Can someone help me out I don't really understand the haloalkane topic.

The following compounds can be made from haloalkanes. For each compound, name a haloalkane which could be used, write an equation and state the essential conditions.

a). Propan-2-ol
Original post by BIOCH3M
Where about's is everyone content wise? My teacher is panicking about finishing.


I do OCR so I've done 3/5 units and parts of my controlled assessment. Lots to do and not enough time. Think imma be finished by Easter.

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Original post by Super199
Can someone help me out I don't really understand the haloalkane topic.

The following compounds can be made from haloalkanes. For each compound, name a haloalkane which could be used, write an equation and state the essential conditions.

a). Propan-2-ol


How do you make an alcohol from a haloalkane first of all?

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Original post by Dylann
How do you make an alcohol from a haloalkane first of all?

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By reacting it with a hydroxide ion. Well by nucleophillic substitution. Well I'm guessing propane is the haloalkane but don't you need a halogen to be attached to that? Does it matter what it is if that is right?
Hi , how much revision have you guys done so far ?
Original post by Super199
By reacting it with a hydroxide ion. Well by nucleophillic substitution. Well I'm guessing propane is the haloalkane but don't you need a halogen to be attached to that? Does it matter what it is if that is right?


You're sort of there. You need a haloalkane because the X-C bond (Where X is a halogen) becomes polarised, meaning C has a slight positive and the halogen has a slight negative charge. Therefore, the negative hydroxide ion could attack the carbon and replace the halogen. The question gave the product of propan-2-ol, meaning the hydroxide ion must have attacked the second carbon. In order for this to have happened, the halogen must have also been on that second carbon. So the original haloalkane was 2-chloropropane (or 2-bromopropane). The condition favoured nuc. sub and not elimination, meaning :OH- acted as a nucleophile which IIRC means the conditions are just room temperature and water...
Original post by Dylann
You're sort of there. You need a haloalkane because the X-C bond (Where X is a halogen) becomes polarised, meaning C has a slight positive and the halogen has a slight negative charge. Therefore, the negative hydroxide ion could attack the carbon and replace the halogen. The question gave the product of propan-2-ol, meaning the hydroxide ion must have attacked the second carbon. In order for this to have happened, the halogen must have also been on that second carbon. So the original haloalkane was 2-chloropropane (or 2-bromopropane). The condition favoured nuc. sub and not elimination, meaning :OH- acted as a nucleophile which IIRC means the conditions are just room temperature and water...

Right got the majority of that. Why can't the halogen be any of the other halogens? Why specifically 2-chloropropane or 2-bromopropane?
Original post by Super199
Right got the majority of that. Why can't the halogen be any of the other halogens? Why specifically 2-chloropropane or 2-bromopropane?



I'm guessing its the secondary carbocation = more stable
Original post by Super199
Right got the majority of that. Why can't the halogen be any of the other halogens? Why specifically 2-chloropropane or 2-bromopropane?


Even though fluorine is highly electronegative (so there will be a strong partial charge on carbon), the C-F bond is extremely strong meaning it's actually quite unreactive, so most exam boards ignore it (the reaction will be very slow and doesn't happy as easily as Cl or Br). Iodine isn't that electronegative (same as Carbon) but it is a very weak bond. Because it's a weak bond, it is easily broken and reacts quickly. I don't see why they might not ask you about Iodoalkanes (perhaps there something going on behind the scenes that is beyond a-level...) Chloro and bromo are just the standard halogens they use :smile:

Original post by shhh123
I'm guessing its the secondary carbocation = more stable


Although this is generally correct, in this case the reason why it is "2" is simply because the product (propan-2-ol) has its hydroxyl (alcohol) group on the second carbon. Since it's a substitution reaction, the original halogen must also have been on the second carbon.

However carbocation stability is something you should definitely always consider during mechanisms - especially electrophilic addition - but it is not a factor in every mechanism. I think the Sn1 mechanism (different to the Sn2 mechanism taught at a-level) involves ionisation of the halogen in which carbocation stability IS a factor, but in Sn2 it is not.
Anyone care to explain the propagation step in free radical substitution. With an example, other than the methane and chlorine one? I understand the initiation and termination step but this one is a bit hit and miss...
Original post by kira1
So I just had a mock exam and got an E, at the end of this year I need a high A, is that possible? If so how ? I feel so stressed and keep imagining myself failing. God forbid


Hi there!

I am an A2 Chemistry student.

I got an A last year at AS level.

In the March MOCKs I got a U grade for Chemistry but that was because I lacked understanding at that time.

To help me understand better I bought the CGP text book which helped contribute to my A grade.

I recommend you get it if you really want that high A grade.

CGP AS Chemistry

SAMPLE PAGES

I also recommend you do lots of past papers so help strengthen your exam technique.

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