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    hi, so how did everyones practical go? mine was rubbish! what came up in yours, and how was it!

    it was an acid base titration... NaOH against an unknown acid.. the titration itself was ok... but the calculations were a bit tricky and i could NOT get the last question!! i had to figure out what the acid was but i couldn't do it what did everyone else do? and how did they go??
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    everyone else found it really hard, never mind! a titration also came up and a delta H, what vboard did you do?

    OCR

    did you do a different practical?
    the only reason i found it reaosnably ok was because i screwed it up last year and had to retake this year! so i did some hard core revision and practised loads of sample questions etc...
    i don't think i did particularly well but i definitely did better than last time!

    ahh! but now i have to start worrying about the A2 practical which is next week! and apparently really difficult oh dear, not looking forward to that one!

    I put that the acid was phenol, C6H5OH (being an organic weak acid). It was a total ****-up for me: I was making up the standard solution by adding distilled water to HA, and the bloody nozzle fell off...water everywhere! The flask was overflowing, the teacher's notes adjacent to my bench were soaked, and I just sat there for a moment with my head in my hands. Another candidate had a leaking burette tap...NaOH all over the place. I'm still trying to come to terms with what is a complete failure on that paper. I did manage to get the second part done OK (Mg experiment), but I'm going to have to really make up for that act of serendipity by flying through the written papers. Worst of all, the invigilator looked at me with a glare of resignation and helplessness.
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    was the c6h120H on the as level paper or the a2. The naoh in my practical went everywhere as well! never mind! did you have to find out what the acid was. were you also giving lists of organic compound and did you have to write about tests to prove whether they were an alchol or an alkene? (in the last part, the planning part!)

    i sooooo know how you feel. i had a similar experience last year. That was mainly due to calculations though. I couldn't do the first one.. and without the answer from the first i couldn't do any of the others.. i was literally in tears at the end of it, being the emotional munt that i am! But you always have the security of retakes if it all goes pear shaped! The second part with the Mg went ok i thought.. but i had a complete mind blank with part (ii) of that section.. about the gas in the flask and whether that would affect the results...????

    with guessing the acid... it's monobasic.. so it has to be something like HCl (ie.. there's only one H) i think that's what it means?!?! i got that completely wrong.. couldn't do that bit!

    in the AS practical the acid was propanoic C3H6O2. has anyone got an idea how to do the A2 plan? it seems really easy, but i am sure there is a tricky bit there!
    i am going to use manganese dioxide for my solid catalyst, is anyone else doing the same? please reply! thanx.

    i didn't get any lists of organic compounds which i had to guess whether they were alkenes or alcohols?? that must be a slightly different paper?

    yeah i am doing the A2 planning thingy but i don't know what to do! i know that i have to use manganese (IV) oxide.. in powder, granules, and sticks to test the effect of surface area..
    but i'm not sure how to set up the experiment.. ie.. apparatus etc..?!?! i'm sure it's simple, but i'm having a complete mind blank.. too much chem.. overload!

    relative molecular mass did you get from your titrations?
    C3H6O2 is 74... i think i got about 72 from my calculations.. is that too far off?
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    how did you know the compound was propanoic acid, did you add potassium dichromate and see the colour change or something?
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    Originally posted by Unregistered
    in the AS practical the acid was propanoic C3H6O2. has anyone got an idea how to do the A2 plan? it seems really easy, but i am sure there is a tricky bit there!
    i am going to use manganese dioxide for my solid catalyst, is anyone else doing the same? please reply! thanx.

    how did you know the the organic compund was propanoic acid?

    i haven't a clue how they figured oput that it was propanoic acid.. i hope that bit wasn't worth loads .. but it didn't show the marks on the side margin like the papers usually do.. hmph...
    well, i think it was a series of calculations you needed to do to determine what it was.. i don't think we were supposed to mix it with anything?

    I got a RMM of about 72 for the acid. I chose the closest element to this which could have been an acid, and that was Bromine.

    HBr, a bit out on the RMM, but it is the only possibility I saw

    To deduce the formula of the acid, you alredy know its an organic acid, therefore it must contain an COOH bit then you add CH3 on the end then keep adding CH2 until u get close to your calculation.

    We did all our OCR AS chem practicals about 3 months ago and had like 3 weeks to write em up. Cept for one which was written up in class. And they were easy cept the one where u had to use hess's law cause I didnt understand it at the time

    Originally posted by jo123
    how did you know the the organic compund was propanoic acid?
    because after you have done the calculations, the molecular mass works out exactly precise. if you had something like 72 or 76 you could have said it was propanoic acid, because this is the closest mol mass to that organoc acid or something.

    The AS chemistry practical -

    My RMM was 59.9, which I rounded up for the next question to 60 for convenience.

    The only organic acids that we learn about in AS chemistry are carboxylic acids, and the functional group for this is COOH.

    The RMM of COOH is 45, so 60-45 is 15. As the prof said, you take CH3 and then if necessary, CH2s to add on until it equals the value closest to your RMM. So yes, the RMM for CH3 is 15, so I didn't need to add on any CH2s as well. This makes the formula CH3COOH. Which is ethanoic acid. Which looks like this:

    H O
    | //
    H - C - C
    | \
    H OH

    (Excuse the bad 'drawing')

    As a side note, by chance, when you opened the bottle at the beginning, the smell that filled the room was remarkably similar to vinegar. The carboxylic acid that we all splash onto our chips is ethanoic acid.



    Then again, the only reason I found this even relatively easy is because I was retaking it. Had I done this particular one last year I think I probably would have got a big zero. Hehe.

    L.
 
 
 

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