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    (Original post by Super199)
    Can someone help me with this question.

    A 25cm3 sample of vinegar was diluted in a 250cm3 volumetric flask. This was then put in a burette and 23.10cm3 of the diluted vinegar neutralised 25cm3 of 0.1M NaOH. What is the concentration of the vinegar in gdm-3.

    CH3CO2H + NaOH --> CH3CO2-Na + H2O.

    Right what I first did is workout the moles of sodium hydroxide which was 0.00250 moles.
    Moles of that is equal to the CH3CO2H, so I worked out the concentration of that which was 0.108dm-3. Then I hit a brick wall. Anyone care to explain what I have to do?
    Ok so you've figured out so far that you have 0.108 mol dm-3 of CH3COOH.

    But you need to convert this value to g dm-3.




    I hope that helps
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    (Original post by Kadak)
    Posted from TSR Mobile

    Question (II)
    Is this the 3 correct isomers?
    I don't think so, because it asks the products that can be formed from hexane. Your products are a variation of different products which can't be formed from radical substitution of hexane.

    I think it should be 1-bromohexane, 2-bromohexane and 3-bromohexane.
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    (Original post by chuckster111)
    I don't think so, because it asks the products that can be formed from hexane. Your products are a variation of different products which can't be formed from radical substitution of hexane.

    I think it should be 1-bromohexane, 2-bromohexane and 3-bromohexane.
    yup
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    Okay, I just made two documents about Organic Chemistry, one to do with the uses of halogenoalkanes and the other relevant to the nucleophillic subsitution mechanisms you're expected to learn for AS

    I've explained everything about nucleophillic substitution in the booklet including the mechanism for both alcohols and amines as well as an explanation behind each step for each mechanism. Hope it helps.

    All the images I took were from either, chemguide.co.uk, chemrevise.org or masterorganicchemistry.com

    Hope it helps

    A rep would nice
    Attached Files
  1. File Type: docx uses of halogenoalkanes.docx (14.6 KB, 101 views)
  2. File Type: docx Nucleophillic Substitution.docx (317.8 KB, 209 views)
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    aqa chemistry
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    (Original post by Isabella~)
    Hiya, I'm doing OCR B
    Hey i'm doing Chemistry OCR B too!

    How is it so far?
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    How am I suppose to know that Ca(OH)2 (s) + NH4Cl (s) releases ammonia gas?

    It's a question, but I don't understand why the answer is
    NH4Cl (s) + Ca(OH)2 --> CaCl2 + 2NH3 (g) + H2O (g)?
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    (Original post by BIOCH3M)
    How am I suppose to know that Ca(OH)2 (s) + NH4Cl (s) releases ammonia gas?

    It's a question, but I don't understand why the answer is
    NH4Cl (s) + Ca(OH)2 --> CaCl2 + 2NH3 (g) + H2O (g)?

    Well if you react them together you're not going to get magnesium oxide are you?
    Just think logically about if you compounds consist of various elements, what standard compounds could be formed as products




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    (Original post by frozo123)
    Well if you react them together you're not going to get magnesium oxide are you?
    Just think logically about if you compounds consist of various elements, what standard compounds could be formed as products




    Posted from TSR Mobile
    Thanks that makes sense, unfortunately chemistry is not my forté
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    What do you actually need to revise for an aqa as level empa written exam? I know I'm probably gonna get a bad grade at the end of the year for the other units but I really need to get a good grade in my empa. Plus my teacher hasn't been in for weeks and she's no help! Can someone please give me some advise on what to revise for my empa exam?😊


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    (Original post by BIOCH3M)
    Thanks that makes sense, unfortunately chemistry is not my forté
    If you need help just holla
    A2 Student atm with an A at AS
    You do edexcel?


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    (Original post by frozo123)
    If you need help just holla
    A2 Student atm with an A at AS
    You do edexcel?


    Posted from TSR Mobile
    I do OCR A, how did you manage to get an A at AS :O
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    (Original post by BIOCH3M)
    I do OCR A, how did you manage to get an A at AS :O
    You just do lots of past papers really


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    Hellloooooo. Okay so I have my evaluative exam tomorrow on the enthalpy change of combustion (OCR A).

    I am just doing some calculations and came across this Q (for those doing OCR A AS its p199 1b):

    Given the following enthalpy changes of combustion C(s) = -394 kJmol, H2(g) = -286kJmol, C2H5OH(l) = -1367 kJmol

    Determine the enthalpy change for:

    2C(s) + 3H2(g) + 1/2O2(g) = C2H5OH(l).


    So I followed the worked example but because I haven't been given the enthalpy change of combustion for oxygen, I had no idea how I was supposed to work out deltaH.

    I did 2(-394) + 3(-286) + unknown enthalpy change of combustion for 1/2 O2 = delta H + -1367.

    = -1646 + unknown enthalpy of combustion for 1/2 O2 - -1367

    = -279 + 1/2 O2 = delta H.


    The answer in the book is -279kJmol-1, but I don't understand! What happens with the oxygen? Doesn't it affect anything? I just can't get my head around it. Thank you to anyone that helps you may be the reason I don't fail tomorrow lol
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    (Original post by Georgiam247)
    Hellloooooo. Okay so I have my evaluative exam tomorrow on the enthalpy change of combustion (OCR A).

    I am just doing some calculations and came across this Q (for those doing OCR A AS its p199 1b):

    Given the following enthalpy changes of combustion C(s) = -394 kJmol, H2(g) = -286kJmol, C2H5OH(l) = -1367 kJmol

    Determine the enthalpy change for:

    2C(s) + 3H2(g) + 1/2O2(g) = C2H5OH(l).


    So I followed the worked example but because I haven't been given the enthalpy change of combustion for oxygen, I had no idea how I was supposed to work out deltaH.

    I did 2(-394) + 3(-286) + unknown enthalpy change of combustion for 1/2 O2 = delta H + -1367.

    = -1646 + unknown enthalpy of combustion for 1/2 O2 - -1367

    = -279 + 1/2 O2 = delta H.


    The answer in the book is -279kJmol-1, but I don't understand! What happens with the oxygen? Doesn't it affect anything? I just can't get my head around it. Thank you to anyone that helps you may be the reason I don't fail tomorrow lol

    Is it because oxygen is an element in its standard state therefore its standard enthalpy is 0? So it effectively doesn't count?
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    (Original post by Disney0702)
    I guess the reason why I love Amount of Substances is because I love Maths and for me Amount of Substances is the best way I can exercise my Maths skills in a different subject.

    No you're not being nosy at all

    I student Maths, Physics and of course Chemistry.

    I dropped English Literature at AS because I knew I would've neglected putting effort into it until the end of the year, even though I loved the subject, I didn't want to put that kind of stress on myself as I knew deep down I will always prioritise Maths and Sciences.

    Uh outside school hours I'd spend at least 4.5 hours a day in general for school work but most of the time I use that time to do Maths homework because my teacher gives my class a crap load to do everyday

    I cannot give you an approx figure as to how many hours I spend for each subject because how I use my time depends on how much work I get given from my teachers and whether I'll have enough time after to do my own independent revision.

    But I think its safe to say most of my weekend is revision and consolidating time.

    I hope that helps.

    Now I hope I'm not being nosy by asking what other A - Levels you do.
    Currently for AS I'm studying Maths, Chemistry, Psychology and ICT. ICT is kind of just the back up and hopefully I can drop that at the end of they year so its just an AS. I also spend a lot of time doing maths homework as we go through one chapter in like 3, 50 minutes lessons so we have a lot of work to do.
    My weekend is kind of homework and then revising as well. I get a lot of chemistry homework too. We get two whole booklets nearly every week for the day after and if we don't do them we just get kicked out the room.


    What are you hoping to do at university can I ask
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    (Original post by zhang-liao)
    Okay, I just made two documents about Organic Chemistry, one to do with the uses of halogenoalkanes and the other relevant to the nucleophillic subsitution mechanisms you're expected to learn for AS

    I've explained everything about nucleophillic substitution in the booklet including the mechanism for both alcohols and amines as well as an explanation behind each step for each mechanism. Hope it helps.

    All the images I took were from either, chemguide.co.uk, chemrevise.org or masterorganicchemistry.com

    Hope it helps

    A rep would nice
    Nice, thanks for making these
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    (Original post by Nidfeo)
    Nice, thanks for making these
    You're welcome

    PM/VM me if you want anyone more revision resources for chemistry, I'm happy making them
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    (Original post by zhang-liao)
    You're welcome

    PM/VM me if you want anyone more revision resources for chemistry, I'm happy making them
    As we're on different exam boards, I don't think some of the content will be relevant, but if I do need anything, I will definitely contact you!
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    (Original post by Nidfeo)
    As we're on different exam boards, I don't think some of the content will be relevant, but if I do need anything, I will definitely contact you!
    Yeah, I guess so, some of the stuff we learn are slightly different but do feel free to contact me though
 
 
 
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