Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta

OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD watch

    Offline

    0
    ReputationRep:
    (Original post by CaoimheMee)
    did anyone get 11.73 for ph of dilute NaOH?

    20cm^3 of 0.0270mol dm^3 NaOH diluted and made up to 100cm^3
    mole of Naoh= 5.4x10^-4
    concenctration of NaOH in 100cm^3 = 5.4x10^-3
    POH=2.267
    so pH= 11.73
    Don't you times it by 5 as the volume goes from 20 to 100cm3
    Offline

    9
    ReputationRep:
    (Original post by Noah T)
    no fault of their own.
    You see, this is my problem, it IS their fault, if you don't know the specification like the back of your hand, and then some, you HAVE NOT done enough revision, none of the calculations were complicated, nothing was off-spec, none of the questions were worded badly, this wasn't some wet and oily lap in the reasonably priced car, this was perfect conditions, it was the choice of every student whether they wanted to drive the reliant robin (not revise) or a McLaren 675LT (revise).
    Offline

    11
    ReputationRep:
    PLEASE someone MAKE THE UNOFFICIAL MARK SCHEME can't bother to revise Biology for tomorrow before looking at this lololol
    Offline

    9
    ReputationRep:
    (Original post by sam_barleymorey)
    Don't you times it by 5 as the volume goes from 20 to 100cm3
    Divide.
    Offline

    11
    ReputationRep:
    Oh I also wonder why people who say they haven't revised at all yet aim for full UMS don't hold matriculation offers from Oxbridge with 7 A* grades at A Level. I'd really like to know. Well done if some of you can do 0 revision and aim for such top grades at A Level
    Offline

    0
    ReputationRep:
    (Original post by sam_barleymorey)
    Don't you times it by 5 as the volume goes from 20 to 100cm3
    No you divide it by 5 volume increase 5 times so concentration decreases 5 times


    Posted from TSR Mobile
    Offline

    1
    ReputationRep:
    (Original post by CaoimheMee)
    did anyone get 11.73 for ph of dilute NaOH?

    20cm^3 of 0.0270mol dm^3 NaOH diluted and made up to 100cm^3
    mole of Naoh= 5.4x10^-4
    concenctration of NaOH in 100cm^3 = 5.4x10^-3
    POH=2.267
    so pH= 11.73

    i got this, dont see how it could be wrong
    Offline

    9
    ReputationRep:
    With regards to the pH of the acid at 60 degrees, it would be either 10.76 (if it was .0270) or 11.76 (if it was .270):

    https://www.google.co.uk/search?q=-l...hrome&ie=UTF-8
    Offline

    9
    ReputationRep:
    (Original post by yiz)
    i got this, dont see how it could be wrong
    EDIT: You didn't take into account that Kw was different, correct way of determining is -log(Kw) + log(OH-)
    Offline

    2
    ReputationRep:
    (Original post by sam_barleymorey)
    Don't you times it by 5 as the volume goes from 20 to 100cm3

    Yeah don't you find the moles then times it by 5 and then work out the concentration by n=c X v? Cuz that's what you would do with redox titration questions and it's the same skill set?
    Offline

    1
    ReputationRep:
    (Original post by sam_barleymorey)
    Don't you times it by 5 as the volume goes from 20 to 100cm3
    That's what I got however I don't think it was that simple, I think you had to use the Kw value at 60 C or whatever
    Offline

    1
    ReputationRep:
    (Original post by GillyTheGhillie)
    Rounding errors. See my previous answer.
    what is the right answer?
    and how many marks would i lose? 1?
    Offline

    0
    ReputationRep:
    (Original post by yiz)
    i got this, dont see how it could be wrong
    Isnt this done at 60C so the value for pKw isnt 14, its 13.03. So the pH would be 13.03-pOH
    Offline

    9
    ReputationRep:
    (Original post by yiz)
    what is the right answer?
    and how many marks would i lose? 1?
    I just edited my original comment, you actually calculated it wrong, Kw is different, you needed to use "-log(Kw) + log([OH-])"
    Offline

    9
    ReputationRep:
    (Original post by milutin767)
    Oh I also wonder why people who say they haven't revised at all yet aim for full UMS don't hold matriculation offers from Oxbridge with 7 A* grades at A Level. I'd really like to know. Well done if some of you can do 0 revision and aim for such top grades at A Level
    Exactly. I guarantee there is not a single person here who came out of that exam feeling like they did awfully, who actually did enough revision.
    Offline

    8
    ReputationRep:
    so is the answer 10.76 or nahh cause im sure thats right...no?

    Posted from TSR Mobile
    Offline

    1
    ReputationRep:
    (Original post by GillyTheGhillie)
    I just edited my original comment, you actually calculated it wrong, Kw is different, you needed to use "-log(Kw) + log([OH-])"
    so how many marks lost?
    Offline

    9
    ReputationRep:
    (Original post by yiz)
    so how many marks lost?
    It was a 2 marker I think, so possibly both, but more likely only 1.
    Offline

    0
    ReputationRep:
    (Original post by HFancy1997)
    so is the answer 10.76 or nahh cause im sure thats right...no?

    Posted from TSR Mobile
    thats what i got
    Offline

    1
    ReputationRep:
    (Original post by GillyTheGhillie)
    Exactly. I guarantee there is not a single person here who came out of that exam feeling like they did awfully, who actually did enough revision.
    I did. Did crap in the paper
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: September 26, 2016
Poll
Do you agree with the proposed ban on plastic straws and cotton buds?

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.