Turn on thread page Beta

Salters Chemistry: 2854: Chemistry By Design 28/06/05 watch

    Offline

    0
    ReputationRep:
    Last question I put hydrogen bonds form between cotton and the dye and that they were easiy disrupted by water.

    But that was obviously wrong. I also described the ir spec thinking i'd get 6 marks for it, AND i said it was the carboxylic acid too, the final nail in the coffin of my A Level Chemistry that was.

    I'm leaving this board now, I hope you all do well and get the grades you want and need and deserve

    Come visit me when I'm serving big macs people
    Offline

    2
    ReputationRep:
    I was quite suprised that there was nothing on Born-Haber cycles or any reaction mechanism explanations.
    Offline

    8
    ReputationRep:
    I absolutely swear there was an OH peak, therefore it was the carboxylic acid compound thing.
    Offline

    17
    ReputationRep:
    I was quite suprised that there was nothing on Born-Haber cycles or any reaction mechanism explanations.
    I wasn't surprised - too busy being relieved :p:

    I absolutely swear there was an OH peak, therefore it was the carboxylic acid compound thing.
    There was a peak at about 1250 and 1050
    But 1050-1300 is described on the data sheet as "alcohols, ethers or esters"
    So it could be the COOH or the ester
    The clue was that the peak at 3000 would have been fat if it was COOH because hydrogen bonding makes it get fat
    Offline

    8
    ReputationRep:
    "There was a peak at about 1250 and 1050
    But 1050-1300 is described on the data sheet as "alcohols, ethers or esters"
    So it could be the COOH or the ester
    The clue was that the peak at 3000 would have been fat if it was COOH because hydrogen bonding makes it get fat "


    wasnt the peak at 3000 only due to an OH bond though, what did that peak supposedly correspond to then?
    Offline

    8
    ReputationRep:
    well i jsut consulted data book...the peak at 3000 has to be due to an OH bond, which isnt present in the ester, therefore it cant be the ester?
    Offline

    0
    ReputationRep:
    A CH bond was about 2900 wasn't it? I wasn't very sure of that question at all! x
    Offline

    1
    ReputationRep:
    I didn't think that peak was at 3000, I thought it was at 2900ish. And I thought it corresponded to an alkane C-H bond. An O-H bond has a peak at 3600-3640 (or 3200-3600 if its hydrogen bonded), and there wasn't a corresponding peak on the spectrum in the question as far as I remember.
    Offline

    8
    ReputationRep:
    Yes that is correct about C-H bonds, but they all contained those, alkane bonds are fairly common and therefore not useful in differentiating between them! and also "Carboxylic Acid O-H Stretch 3000 - 2500 (broad, v) "
    Offline

    2
    ReputationRep:
    Hey everyone, that wasn't nearly as bad as it could have been! I could've kissed someone for that IR 8 marker, and the reagents/conditons of oxidising an alcohol to an acid? I think im turning religious, thank the lord!

    There were some tough questions, a few calculations I made up numbers by tapping the calculator randomly (im not too hot at those questions lol) but all in all, it went a lot better then I was expecting! Now... to see what the overall grade is... *runs and hides in panic*

    Best of luck everyone, try not to think about it too much, theres nothing else we can do anymore!!

    NO MORE EXAMS!!!!!!!!!!!1 (sorry if you have any left!)
    Offline

    1
    ReputationRep:
    Lol moojoo, I'm aware that all of them have C-H alkane bonds! :p:

    I was just pointing out that having a peak at around 3000 doesn't necessarily mean it has an O-H as you said, and that the peak wasn't really at 3000 in my opinion, more at 2950 or something.

    I can't see how it would be either of the compounds containing an alcohol, there weren't any peaks in the region for an alcohol O-H bond.
    Offline

    8
    ReputationRep:
    Lol, that peak was in the region for a carboxylic acid O-H bond!
    Offline

    0
    ReputationRep:
    it was the compound with the carboxylic acid. there was a peak for the O-H bond in a caboxylic acid and a peak for the C=O bond in a carboxylic acid.
    Offline

    1
    ReputationRep:
    Are you sure? All of the people in my class said it was the one with the ester...
    Offline

    8
    ReputationRep:
    (Original post by AmS)
    it was the compound with the carboxylic acid. there was a peak for the O-H bond in a caboxylic acid and a peak for the C=O bond in a carboxylic acid.
    exactly! you have the right idea lol
    Offline

    8
    ReputationRep:
    well im pretty confident and most people i spoke to did that one too, sorry if i was getting angry at u amie lol, i jus need to do well and was scared i got it wrong! x
    Offline

    1
    ReputationRep:
    I'm scared too! I mean, I know I buggered up most of the question because I didn't read it properly and ignored the nmr part of it. But I just can't see how it can be either of the ones without an ester, since both of those had alcohol groups and there wasn't a peak for the O-H in an alcohol, as far as I remember. But my memory might not be very good this long since the exam
    Offline

    17
    ReputationRep:
    Urgh this argument had to start after i packed up all my chem stuff to take back into school didn't it

    Ok the absorbpitons were at 1750, 1250 and about 1050 if i remember correctly as well as a lesser absorption at 3000

    1735-1750 is an ester. 1700-1725 is a carboxylic acid. So that could be either
    1250 and 1050 are both covered by the C-O bond at 1050-1300 which can correspond to "alcohols, ethers or esters" so once again that could be either
    The bond at 3000 could be a) a C-H bond at 2950, most likely as they all have CH bonds and otherwise there wasn't a peak for that at all or b) a carboxylic acid O-H group. However that OH group (unlike the one in an alcohol) would allow hydrogen bonding and is therefore a very broad peak - more like a hill than a mountain. The peak ~ 3000 was very sharp and was therefore NOT a carboxylic acid peak

    Therefore it MUST be the ester
    Offline

    8
    ReputationRep:
    im sure u did fine overall, i just mucked up all the intermolecular force questions and everythign! we will both be alrigth fingers crossed
    Offline

    1
    ReputationRep:
    Its ok, I only need a C anyway, so that means I needed something like 43/120 on that paper!
 
 
 
The home of Results and Clearing

3,195

people online now

1,567,000

students helped last year

University open days

  1. London Metropolitan University
    Undergraduate Open Day Undergraduate
    Sat, 18 Aug '18
  2. Edge Hill University
    All Faculties Undergraduate
    Sat, 18 Aug '18
  3. Bournemouth University
    Clearing Open Day Undergraduate
    Sat, 18 Aug '18
Poll
A-level students - how do you feel about your results?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.