Join TSR now and get all your revision questions answeredSign up now

OCR Salters Chemistry F335 12th June 2013 Exam revision thread Watch

    Offline

    0
    ReputationRep:
    Name:  NMRSPEC.JPG
Views: 239
Size:  25.2 KB

    Guysss can I get some help with nmr spectroscopy? The mark scheme says neither of the peaks have splitting Can you not have splitting when the H is bonded to an O ? or when there is in O next to the C?
    Offline

    0
    ReputationRep:
    (Original post by Salmonidae)
    So the answer is 2 electrons per bond and the best way to think about it is purely logically. Between 2 hydrogens each with one electrons and each of the Boron's one last electron that is free to bond there are four electrons available for these three centre bonds. Therefore it has to be 2 each!

    I had never come across this before doing that paper the other day either!

    S
    whaaat that's what I thought but then I thought if there are four of these bonds then there must be 1/4 of all the electrons so 1 arghhhhhh oh wait, haha silly me
    a three centre bond is B----H-----B and not just B----H which I was trying to work out xD
    Offline

    0
    ReputationRep:
    (Original post by Tikara)
    Name:  NMRSPEC.JPG
Views: 239
Size:  25.2 KB

    Guysss can I get some help with nmr spectroscopy? The mark scheme says neither of the peaks have splitting Can you not have splitting when the H is bonded to an O ? or when there is in O next to the C?
    There is no splitting of hydrogens in the OH and NH bonds or of the hydrogens on the next door carbons
    Offline

    1
    ReputationRep:
    (Original post by super121)
    There is no splitting of hydrogens in the OH and NH bonds or of the hydrogens on the next door carbons
    Sorry misclicked at derepped you

    This is correct, worth remembering splitting only occurs for hydrogens on adjacent CARBONS, not any other element.
    Offline

    0
    ReputationRep:
    (Original post by super121)
    There is no splitting of hydrogens in the OH and NH bonds or of the hydrogens on the next door carbons
    thanks very much thats cleared up alost - I couldn't really seem to find any of that in the chemical ideas or rev book
    Offline

    0
    ReputationRep:
    (Original post by Salmonidae)
    Sorry misclicked at derepped you

    This is correct, worth remembering splitting only occurs for hydrogens on adjacent CARBONS, not any other element.
    lmao- yeah I was just about to ask whether I should assume if it's not a carbon adjacent then there's no splitting so thanks for that
    Offline

    0
    ReputationRep:
    (Original post by Salmonidae)
    Sorry misclicked at derepped you

    This is correct, worth remembering splitting only occurs for hydrogens on adjacent CARBONS, not any other element.
    It's ok

    (Original post by Tikara)
    thanks very much thats cleared up alost - I couldn't really seem to find any of that in the chemical ideas or rev book
    Welcome
    Yea, salter's just expect us to know some things :rolleyes:
    Offline

    0
    ReputationRep:
    omg I can't ever believe how a solid buffer question gets 1 mark and no indication in the mark scheme whatsoever of how to properly do it - must I be doing them wrong or something?

    can anyone help on Jan 12 question 5 fii ? It's another annoying proportion thing but I got the previous bit right (somehow) but can't get 2.73 for the answer
    Offline

    0
    ReputationRep:
    (Original post by Tikara)
    omg I can't ever believe how a solid buffer question gets 1 mark and no indication in the mark scheme whatsoever of how to properly do it - must I be doing them wrong or something?

    can anyone help on Jan 12 question 5 fii ? It's another annoying proportion thing but I got the previous bit right (somehow) but can't get 2.73 for the answer
    Go back a couple of pages to something like page 8 or 9 someone's answered it well there
    Offline

    0
    ReputationRep:
    Hi can anyone help me on the June 2010 paper Q2f, it's an NMR guess the compound one, I can't see how it is CH3CH2OCH2CH3 :/

    Thanks
    Offline

    0
    ReputationRep:
    (Original post by totw)
    Go back a couple of pages to something like page 8 or 9 someone's answered it well there
    lmao!! turns out I asked the question after getting stuck on this question the first time I did this paper and forgot about it oh god if this is what my memory is like then I'm reaaaally worried for this exam now xD
    Offline

    0
    ReputationRep:
    for june 2012 question 5e)

    the last mark in the mark scheme is for saying 'Entropy loss of water/more order in water'

    does anyone one know what it means.. I am not sure how to put it in a sentence that make sense? thanks
    Offline

    0
    ReputationRep:
    (Original post by tsr1)
    for june 2012 question 5e)

    the last mark in the mark scheme is for saying 'Entropy loss of water/more order in water'

    does anyone one know what it means.. I am not sure how to put it in a sentence that make sense? thanks
    In entropy in water decreases so there is less disorder
    Offline

    0
    ReputationRep:
    (Original post by super121)
    In entropy in water decreases so there is less disorder
    so in solid, there is no water and therefore, there is low entropy?
    Offline

    0
    ReputationRep:
    (Original post by tsr1)
    so in solid, there is no water and therefore, there is low entropy?
    I don't know what the question is, but entropy decreases going from a liquid to a solid
    Gases have the most entropy while solids have the least
    Offline

    0
    ReputationRep:
    (Original post by super121)
    I don't know what the question is, but entropy decreases going from a liquid to a solid
    Gases have the most entropy while solids have the least
    salts consists of small highly charged ions e.g. ca+2, S(sys) has a negative value

    suggest why S(sys) is often more positive for dissolving processes but negative for the dissolving of some calcium salts

    so, the last mark was for saying 'entropy loss of water / more order in water ' which I was confused about...
    Offline

    0
    ReputationRep:
    (Original post by tsr1)
    salts consists of small highly charged ions e.g. ca+2, S(sys) has a negative value

    suggest why S(sys) is often more positive for dissolving processes but negative for the dissolving of some calcium salts

    so, the last mark was for saying 'entropy loss of water / more order in water ' which I was confused about...
    It's just saying that there is less entropy in water, because in the question we were told that Ca ions have a negative values for deltaSsys, suggesting that entropy decreases.
    Remember, if deltaSsys is negative, entropy decreases and vice versa
    Offline

    0
    ReputationRep:
    (Original post by Ikklemini)
    I'm doing the jan 2011 paper and not sure about question 4) (f)

    It says explain what is meant by a buffer solution and how a buffer solution works by referring to the equilibrium in equation 4.1.


    resists pH change AW 
    when acid/alkali added 
    in small quantities 
    equilibrium moves to left when acid added [ORA for alkali] 
    removing acid / H+ [ORA for alkali]  large concentration of HCO3– 


    The mark scheme had this answer but I dont understand the change in equlibrium- could someone explain this please!! Thank you x


    Can someone please help with this question ?

    Posted from TSR Mobile
    Offline

    0
    ReputationRep:
    (Original post by Ikklemini)
    Can someone please help with this question ?

    Posted from TSR Mobile
    It moves to the left to counteract the change of the acid being added, because there's a higher conc of acid on the right
    Offline

    1
    ReputationRep:
    (Original post by Jlane5000)
    Hi, sorry if i'm being really stupid but could you walk me through how you got the answer. I've been trying to figure it out for an hour. I thought to work out the conc of H+ that it was ka * [HA]/[A-]

    but in your calculation you have the salt being divided by the acid, and i'm confused why. Sorry if i'm being thick, i've been staring at it too long and my brain has turned to mush
    If you look in Chemical Ideas on Page 191 the equation I'm using in under the text saying "If we make use of assumptions 1 and 2 above"
 
 
 
Poll
Which web browser do you use?

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

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