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    According to my lecturer the answer is x = 10.... but how did people gat this??? i am so confused with this and very very stuck!!!!!!!

    Any one know any good reference books that will help with this exercise...i cant find any!!!!!!!!!!!!!!!

    shimmer
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    Any one know any good reference books that will help with this exercise...i cant find any!!!!!!!!!!!!!!!
    im using my revision guide
    im sure theres something in the OCR txt book.
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    (Original post by suzukiescudo)
    im using my revision guide
    im sure theres something in the OCR txt book.
    There isn't relevent info in course books. I remember battling with this for last year's AS Chem planning on finding composition of MgCO3 in a digestion tablet. The point is you have to look up stuff by research.That's why they make it that hard. I've found this year's planning soo much easier, just because I've researched more.
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    (Original post by Shimmer)
    According to my lecturer the answer is x = 10.... but how did people gat this??? i am so confused with this and very very stuck!!!!!!!

    Any one know any good reference books that will help with this exercise...i cant find any!!!!!!!!!!!!!!!

    shimmer
    the answer may have been 10 for you but not for everyone. there are 3 possible answers, 1, 7 and 10.

    If you did a titration then the person who supplied the chemicals would have chosen either monohydrate, hepahydrate or decahydrate.

    the no.moles H2O can only be obtained from experimentation.
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    oky now im stuck!
    in the planning sheet question....

    it states the following:

    'Your plan should include the following:

    point4, it says
    A specimen calculation to show how the number of moles of water of crystallisation would be calculated from the first experiment involving heating.

    im brain dead! is this when you do the weighing thingy?
    i swear i'm thick as a plank! iduno wot to do
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    (Original post by suzukiescudo)
    oky now im stuck!
    in the planning sheet question....

    it states the following:

    'Your plan should include the following:

    point4, it says
    A specimen calculation to show how the number of moles of water of crystallisation would be calculated from the first experiment involving heating.

    im brain dead! is this when you do the weighing thingy?
    i swear i'm thick as a plank! iduno wot to do
    You know Mr sodium carbonate. So weigh before decomposing, weigh after. The difference is the water lost.
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    im confused. is it even possible to get an answer to xH20 without performing the experiment?

    are the people saying its 10 already done the practical or something?

    so lost.:confused:
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    (Original post by tozhan)
    ummmm you cant work this out just using maths, i assume you did the titration...

    im going to do some preliminary work next week, can you tell me if you found any problems that i should watch out for?
    As tozhan says.. you can only work it out by experimentation. The people who did maths did a titration..(or they're just lucky by coincidence) The rest of us only make educated guesses because we know the three known forms of hydrates for Sodium Carbonate.
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    this isnt making sense, why have all you guys worked out answers, the planning doesnt even ask you to find one, it says show a method by which it can be found.
    The heating method requires a specimen calculation so a calculation process for this makes sense.
    but for the titration why CALCULATE an answer beforehand to say what the answer actually is for the titration.
    secondly should is only be 800 words and from what ive read alot of the plans you guys will come up with will be much much longer.
    read the 5 bullet points, i mean properly, thats what it asks for so in order to max out at 800 words why give a longer answer than is actually ASKED for
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    the titrations performed are purely to give you a better idea of what method is required. you do not have to write it up if you think it will cause you to go over the word limit. they do ask for a theoretical calculation involving the thermal decomp. so knowing how many moles are likely to exist in your sample is a bonus.

    it may seem like extra work but those of us who enjoy chemistry cant spend enough time in the labs! <<< chem geek.
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    thats true and i didnt mean that in a rude way, but i actually just wanted to know the point. its understandable i guess
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    (Original post by Wacther)
    thats true and i didnt mean that in a rude way, but i actually just wanted to know the point. its understandable i guess
    I agree with you entirely. I've just finished my plan, and i've used no real figures in any of the actual calculations. I've just said that I'd do such and such with such a mass and such a volume. So precisely that.. it is just a plan. It was just interesting, and I did a bit of reading round before I did the plan to make sure that my plan was feasible. That's what all the discussion was about. Furthermore, we were trying to answer questions by other people about whether their values were right/wrong.. and that's precisely what we said.. you can't figure it out by calculation.. only by experimentation. I think it was confusing for people though.. and it was easy to think that you had to actually really figure it out with real figures. Also.. its helpful to use figures if you'd wanted to use some for an example. Having said that my word count was 1300..got round it with putting everything in tables. (sure that doesn't surprise anyone...
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    (Original post by Craghyrax)
    my word count was 1300..got round it with putting everything in tables.
    jeez. wouldnt they notice that its like... 500 words over?
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    (Original post by mengzor)
    jeez. wouldnt they notice that its like... 500 words over?
    I don't know. I did it last year (retaking AS Chem), and I got away with it as far as I know. The lecturer told us that they don't count things that are in tables. So I just put everything I want to say in bullet points surrounded by tables. My 800 words were the intro, the assessment and risk analysis pretty much. I don't do word limits very well!
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    on topic of the planning...
    it would be better to use phenolphthalein indicator over methyl orange right?
    (in the titration method)
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    2 questions:

    why do you heat the crucible with the lid on?
    why do you heat it with the lid off?
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    lid on if you dont want oxygen reacting with whatevers in the crucible
    lid off if you want water vapour to escape
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    what have people written about the risk assesment?
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    but why are you meant to heat it gently first with lid on, and then take lid off and heat strongly? youre meant to do both. i dont know why.
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    on topic of the planning...
    it would be better to use phenolphthalein indicator over methyl orange right?
    (in the titration method)
    i think methyl orange is supposed to be the better indicator, somehting on chemguide about phenophatlein or however u spell it, showing the wrong end point or sumfin. i tried to search it up on google but thus far it hasnt been a very heplful search on the subject
 
 
 
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