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# AS Chemistry- helping each other out! watch

1. Hi guys. Anyone doing the AQA ISA (on group 2 metals and mole calculations) anytime soon?
2. (Original post by Science100)

I have been asked to calculate enthalpy change of formation for N2O using data given.

table says:
C + N2O -> CO +N2 -193 KJ mol-1 (not specified whether C or F)
C +1/2O2 -> CO -111 KJ mol-1 (again not specified)

how to do I know whether to draw a Hess' cycle where the arrows point upwards from the elements (formation) or whether to draw one where they point down to combustion products (combustion) IF DONT KNOW WHETHER THE TABLE VALUES ARE FOR COMBUSTION OR FORMATION ENTHALPY CHANGE??? PLEASE HELP ME EVEN MY TACHER COULD NOT EXPLAIN THIS TO ME!!!!!!!!!!! a clear description would help Can u tell me how to figure out if its a combustion cycle AND ALSO how to figure out if its a formation cycle! thanks!
It seems that you lack a fundamental understanding of what's going on here.

C + N2O -> CO +N2 -193 KJ mol-1
This is neither the enthalpy of combustion or formation. This is simply the enthalpy change for the reaction.
C +1/2O2 -> CO -111 KJ mol-1
This is just the enthalpy of formation for carbon monoxide

You (should) know that the enthalpy of formation is the enthalpy change for the formation of one mole of a compounds from its elements in their standard states.
i.e.

so you need to find a way to get to this equation from the two that you've been given

Spoiler:
Show

3. (Original post by Disney0702)

Oh my! I hated Organic Chemistry at AS and I still hate it at A2, you must be those rare weirdos that like it, take it as a compliment mate

Thanks for the support. I have to say that organic chemistry is something I like as we then get other chapters like amount of substance and bonding (urgh!) that I just can not stand
What advice could you give someone like me
4. (Original post by AyshaU)
Thanks for the support. I have to say that organic chemistry is something I like as we then get other chapters like amount of substance and bonding (urgh!) that I just can not stand
What advice could you give someone like me
WOAH!!! Amount of Substances is my baby, I love that topic!

The best advice I can give you is honestly to just do past paper questions.

This had helped me so much last year as not only had it helped strengthen my understanding of the topic it also taught me the language of the exam so I'm not completely clueless when I read a question.
I'm sure you may have noticed that the way AQA phrase their questions can be quite obscure sometimes that it makes you question yourself as to whether you were taught the topic in question.

Amount of Substances is DEFINITELY a topic that will come up in your Unit 1 exam so do as much questions as you can on it and I promise you it'll be a breeze in the end.
5. (Original post by Hayley Williams)
Just look through your textbook and make some notes! It's up to your what you get, i had a crap teacher and still got an A. Had to work my arse off but i got it
I ended up watching some E.Rintoul videos which helped a lot, but haven't got my mock back yet for unit 2. I got a C in unit 1, I can easily bring that to a B I think or even an A, it's unit 2 that's the real problem for me now

Doing past papers has helped so much as well. I never realised how good they were.
6. Dsss
7. (Original post by Disney0702)
WOAH!!! Amount of Substances is my baby, I love that topic!

The best advice I can give you is honestly to just do past paper questions.

This had helped me so much last year as not only had it helped strengthen my understanding of the topic it also taught me the language of the exam so I'm not completely clueless when I read a question.
I'm sure you may have noticed that the way AQA phrase their questions can be quite obscure sometimes that it makes you question yourself as to whether you were taught the topic in question.

Amount of Substances is DEFINITELY a topic that will come up in your Unit 1 exam so do as much questions as you can on it and I promise you it'll be a breeze in the end.
Like you said to me when we were talking about organic, how the hell can you love amount of substance, its an okay topic and I'm sure I've revised pretty much every question that is out there as I've started doing the same papers again. I know it comes in every paper and that scares me. I've just got bonding to cover and I have finished my CHEM1 revision. then onto CHEM2 (yay!!)

If iI' not being nosy can I just ask what other A-levels did you do and how much time did you spend on each of these per week.
If you don't want to answer I honestly would understand
8. (Original post by abzaa)
Hey I need help, I hav my chemistry ISA coming up and I havnt revised for cause my mum passed away, can some plz help me on the ISA it's on titration any help would be really appreciated thanks, I'm will to exchange other info on empa for year 13
TSR Rules:

Practical exams in science subjects are taken by different groups of students across an extended period of time. This means that some people will have finished an exam that hasn't even been started by others. Along similar lines to the restrictions for written exams discussed above, we'll close and/or remove any threads requesting/disclosing specific details of practical exams. However, we realise that you may want to talk about the exams with others once you've completed them, and as such it's acceptable to discuss the practicals on a general level. For example, asking others about the difficulty of the exams as a whole should be fine in most cases. It's also acceptable to ask for general advice prior to sitting an exam, such as on how to draw graphs, or what words mean within questions.
Again, these rules apply to private messages as well as to posts on the public forums. Please see the Exam Discussion Rules page for more detailed information.
9. (Original post by Hadiqa malik)
PlZ can I get unit 2'chemistry june 2014 past paper its urgent aqa board

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Unless AQA has published the information onto their website, you cannot gain access to it without breaking copyright laws.
10. (Original post by anoymous1111)
anyone done the qualitative on investigating reactions of salts and making solutions of salts?

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TSR Rules:

Practical exams in science subjects are taken by different groups of students across an extended period of time. This means that some people will have finished an exam that hasn't even been started by others. Along similar lines to the restrictions for written exams discussed above, we'll close and/or remove any threads requesting/disclosing specific details of practical exams. However, we realise that you may want to talk about the exams with others once you've completed them, and as such it's acceptable to discuss the practicals on a general level. For example, asking others about the difficulty of the exams as a whole should be fine in most cases. It's also acceptable to ask for general advice prior to sitting an exam, such as on how to draw graphs, or what words mean within questions.
Again, these rules apply to private messages as well as to posts on the public forums. Please see the Exam Discussion Rules page for more detailed information.
11. Just a reminder for everyone, I'm not sure if this has been said already but I don't think anyone is allowed to share any ISA/EMPA (irregardless of exam board) on TSR.

Additionally, I don't believe anyone should be sharing the 2014 June paper (the most recent papers) on this thread or across the forum for chemistry (or any other subject for that matter either) as well.

I've already been PM'ed a few times for Edexcel ISA papers/June 2014 papers which are not allowed to shared on this forum.

Sharing those resources (whilst they are locked or not available on the exam boards website) could be classed as cheating which I'm sure that no one should be doing

Apologies if anyone takes any offence, I'm just saying it to prevent any cheating from occuring on TSR.
12. Oooppss sorry won't happen again
13. Has anyone received the advance notice booklet for OCR B chemistry yet?
If so we could discuss possible questions (what our teacher think and what we think), I don't think it's a problem since it states "Candidates should be able to discuss the Advance Notice freely" on the booklet. Thanks!

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14. Anyone care to help me with displayed/structural formula

3-methylbutan-1-ol

Is the structural formula
CH3CH(CH3)CH2CH2OH

The next one is to draw out CH3CH3COCH(CH3)2

is that 2-methyl-pentan-3-one?

What does 3-oxobutanal look like?
15. When silicon tetrachloride is added to water, the following reactionoccurs:
SiCl4(l)+ 2H2O(l)SiO2(s)+ 4HCl(aq)
1.2g of impure silicon tetrachloride was dissolved in excess water, andthe resulting solution was made up to 250 cm3.A 25 cm3portion of the solution was then titrated against 0.10 moldm-3sodium hydroxide, and 18.7 cm3of the alkali were required. What was the percentage purity of thesilicon tetrachloride?

I've been stuck on this for a while now. Any help would be appreciated
16. (Original post by Super199)
Anyone care to help me with displayed/structural formula

3-methylbutan-1-ol

Is the structural formula
CH3CH(CH3)CH2CH2OH

The next one is to draw out CH3CH3COCH(CH3)2

is that 2-methyl-pentan-3-one?

What does 3-oxobutanal look like?
you're right for the first two, 3-oxobutanal has the structural formula of CH3COCH2CHO
you're right for the first two, 3-oxobutanal has the structural formula of CH3COCH2CHO
What does oxo mean?

I have a few more if you don't mind checking.

2,2-diflourobutanoic acid.

CH3CH2C(F)2COOH

1-chlorobutan-2-one

CH2ClCOCH2CH3

The next one is to name the thing. The structural formula is (CH3)2C(OH)CH2COOH
No idea how you name this.
It has an alcohol and a carboxylic acid?

Similar problem with CH2=CHCH2COOH
Which I put as But-1-eneoic acid

Another one CH3CH(OH)CH2COCH3
Which I don't even know how to display

Last one is CCl3COOH
1,1,1-trichloroanoic acid? haha if that exists.

18. (Original post by TheGreatImposter)
Has anyone received the advance notice booklet for OCR B chemistry yet?
If so we could discuss possible questions (what our teacher think and what we think), I don't think it's a problem since it states "Candidates should be able to discuss the Advance Notice freely" on the booklet. Thanks!

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Printed it today. I read it and thought something along the lines of "hmmm, I have no idea what to take from this."
19. (Original post by Super199)
What does oxo mean?

I have a few more if you don't mind checking.

2,2-diflourobutanoic acid.

CH3CH2C(F)2COOH

1-chlorobutan-2-one

CH2ClCOCH2CH3

The next one is to name the thing. The structural formula is (CH3)2C(OH)CH2COOH
No idea how you name this.
It has an alcohol and a carboxylic acid?

Similar problem with CH2=CHCH2COOH
Which I put as But-1-eneoic acid

Another one CH3CH(OH)CH2COCH3
Which I don't even know how to display

Last one is CCl3COOH
1,1,1-trichloroanoic acid? haha if that exists.

If a molecule has both ketone and aldehyde in it than you take the aldehyde C=O to be first priority meaning you count from that carbon and the ketone
C=O is given the suffix oxo-

4-hydroxypentanoic acid would be CH3CH(OH)CH2CH2COOH you count from the carbon in the carboxyl group

but-3-enal would be CH2=CHCH2CHO

the one where you have to name it would be 3-hydroxy-3-methylbutanoic acid

and lastly with the three chlorines that would be 2,2,2-trichloroethanoic acid
20. (Original post by panda14)
Printed it today. I read it and thought something along the lines of "hmmm, I have no idea what to take from this."
Same but I think we're gonna through it in class soon and apparently it's worth 20 marks so I wanna make sure I smash them since they practically give it away

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