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    (Original post by ShadowStorm)
    I wouldn't go blahing all over that it's brilliant yellow, because I'm fairly certain you might be wrong. Weak acid + Strong base means use something with a range above 7. You follow where the change in pH is fastest. I can't remember the range for brilliant yellow, but thymol blue seemed the most logical choice because of this fact.
    The end point of the reaction is irrelevant - neutralisation always occurs at ph 7. You want to find the point where change is fastest.
    Thymol blue had a pH range of up to 6.8, the brilliant yellow had a max pH range of above 7, about 7.4 i thin and therefore it must be brilliant yellow, it is a weak acid pH 3.4 and a strong acid pH 12, so ur actually wrong - no other way i can put it and wot the f*** are u on about iot doesnt matter about neutralisation occurs at pH 7, thats not answering the question its a load of bull ur just using to make it sound right - ur supposed to look at the equivalance point.

    **** I need a chill pill
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    i'm really scared. will someone who has done chemistry papers tell me or just try and calm my nerves please/

    i just got scared not being able to define what the calcium phosphate was. i really need to get the A in this subject and i feel today i've wreck every possible chances


    oh btw, the answers for the gases i got a similar figure, but its in dm cubed surely?


    help. i got synoptic bio tommorow. i feel so terrible. awful.
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    (Original post by dodster)
    i also got Ca3 (PO)4 and it balanced etc.
    first q- initial rate
    = definition of rate of reaction with initial before it
    i think the initial amount of moles of reactant used in given time

    it was pretty simple exam- i was happy with it and nice and easy shame the boundary might go up .
    NOW DOES ANYONE KNOW WHY THE LAST PART OF THE LAST QUESTION HAD
    BOLD WRITING? i got the answer - 0.06/0.5 and 0.03/0.5 to get the moles or conc i cant remmber but what the f*** did it have to do with gaining 2 electrons?
    and what were the optimum conditions for the reaction? hig temp/pressure
    i got the rest of that q fine
    The thing about electrons had to do with the order of acidic strength which was to do with pKa - as it increased so did strength, I also got low pressure and temp, i know it slows the rate but what was the problem with preessure - i just wrote too expensive to maintain but i know thats bull
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    (Original post by Pumpkinfoodle)
    i'm really scared. will someone who has done chemistry papers tell me or just try and calm my nerves please/

    i just got scared not being able to define what the calcium phosphate was. i really need to get the A in this subject and i feel today i've wreck every possible chances


    oh btw, the answers for the gases i got a similar figure, but its in dm cubed surely?


    help. i got synoptic bio tommorow. i feel so terrible. awful.
    Its dm3 or cm3 doesnt matter, cm3 is 1000 x dm3, so i got 30 and 60 (NaOH) in cm3, thats .03 dm3 and .06 dm3.

    But if ur only worrying about that question dont - if u think you got above 48/60 thats an A

    i got biology tomorrow and ICT, so i dunno wot to do but revise for the options module, mines microbes u?
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    (Original post by ShadowStorm)
    I wouldn't go blahing all over that it's brilliant yellow, because I'm fairly certain you might be wrong. Weak acid + Strong base means use something with a range above 7. You follow where the change in pH is fastest. I can't remember the range for brilliant yellow, but thymol blue seemed the most logical choice because of this fact.
    The end point of the reaction is irrelevant - neutralisation always occurs at ph 7. You want to find the point where change is fastest.
    i'm with you dude! didnt actually work out where the equiv point was, just drew the standard weak acid/strong base curve which has the vertical bit at roughly pH8. hence i chose thymol blue.
    all in all not too bad a paper really. some odball questions but nothing toooo difficult.
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    (Original post by allodoxa)
    I'm having trouble remembering the question now, but I thought it stated that the half life was 3 seconds? Therefore after 3 seconds, the concentration would have halved?
    yeah i put that too. and that HCl conc didnt change because it was only a catalyst. Equili3ium, does your calc. end up with half the conc after 3s? if so then it works either way.
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    (Original post by noggin)
    i'm with you dude! didnt actually work out where the equiv point was, just drew the standard weak acid/strong base curve which has the vertical bit at roughly pH8. hence i chose thymol blue.
    all in all not too bad a paper really. some odball questions but nothing toooo difficult.
    Thymol blue had a pH range maximum of 6.8
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    (Original post by starcrossed)
    i can honestly say that i thought that paper was hardddd!!!nuffin like ne of the past papers, a few easy qs but soo many to catch u out. like for the qs where it sed write the rate equation, did u put hcl in the rate equation or not. for the 2nd from last qs which acid did u say was the strongest? i cant beleive there was no bufffers i had got my head around them.
    I said that H3PO4 was the strongest as it had the lowest pKa value.

    I did put HCl in the rate equation, but not sure if it should have been there as it was only a Catalyst, but it was in 1st order, so I assumed it should be in the equation.

    Buffers are cool, why weren't there any!

    Thymol Blue was 8 - 9 I thought.
    Brilliant Yellow was 6 - 8 I think...?
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    (Original post by Stunt-101)
    Thymol blue had a pH range maximum of 6.8
    nuh-uh, it was something like 7-8 or something. definitely had an 8 in there.
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    (Original post by ThunderCat8)
    I said that H3PO4 was the strongest as it had the lowest pKa value.

    I did put HCl in the rate equation, but not sure if it should have been there as it was only a Catalyst, but it was in 1st order, so I assumed it should be in the equation.

    Buffers are cool, why weren't there any!
    The values givern were Ka not pKa if the numbers were pKa they would all have been of the order 0-10, not x x 10^-whatever, thus you got it the wrong way around, if i remember the question right
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    (Original post by cobra01977)
    The values givern were Ka not pKa if the numbers were pKa they would all have been of the order 0-10, not x x 10^-whatever, thus you got it the wrong way around, if i remember the question right
    i put that the one with biggest Ka had biggest conc of H+, hence strongest (lowest pH)...is this right?
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    (Original post by noggin)
    nuh-uh, it was something like 7-8 or something. definitely had an 8 in there.
    yes it was definatly >7
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    Yeah, I know the numbers were Ka, but I converted them to pKa by doing -logKa.

    Is a low pKa a strong acid like a low pH is? That is what I assumed.
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    (Original post by noggin)
    i put that the one with biggest Ka had biggest conc of H+, hence strongest (lowest pH)...is this right?
    yes
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    (Original post by cobra01977)
    yes
    good egg
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    (Original post by cobra01977)
    yes it was definatly >7
    i think we'll have to agree to disagree. unless anyone else wants to join in?
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    (Original post by ThunderCat8)
    Yeah, I know the numbers were Ka, but I converted them to pKa by doing -logKa.

    Is a low pKa a strong acid like a low pH is? That is what I assumed.
    larger the pka weaker the acid
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    (Original post by cobra01977)
    smaller the pka weaker the acid
    WRONG!

    "A strong acid has a large Ka value (or a small pKa value). "

    from http://www.revision-notes.co.uk/revision/128.html

    Aha! I am right! Phew!
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    (Original post by ThunderCat8)
    Bugger!
    donna worry, twas only one piddling mark.
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    (Original post by cobra01977)
    larger the pka weaker the acid
    Haha! Good change there mate!
 
 
 
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