Turn on thread page Beta
    Offline

    0
    ReputationRep:
    i would have thought phenolphthalein would be easier to see a colour change
    purple to clear is easier than red to yellow.


    also , what is a good amount of time to heat the Crucible in method 1?
    and at what flame (blue or roaring)
    Offline

    0
    ReputationRep:
    (Original post by mengzor)
    on topic of the planning...
    it would be better to use phenolphthalein indicator over methyl orange right?
    (in the titration method)
    definatly not phenolphalein! its end point is 9.4 or sumthing. that is way outside the range of a Strong acid/Weak base titration. Methyl Orange is a good one. Its end point is within the correct range. Bromothymol blue is also a good choice.

    (Original post by sona)
    why do you heat the crucible with the lid on?
    why do you heat it with the lid off?
    you heat with the lid off on gentle heat to let the gases escape.

    you heat on full heat wit the lid on to avoid getting bits everywhere if it were to explode due to air trapped inside rapidly expanding. Also, if you want to stop your sample reacting with the atmosphere.

    you weigh your sample with the lid ON because the warm vapours set up convection currents above your sample and cause fluctuations in your measurments.
    Offline

    2
    ReputationRep:
    thanks
    Offline

    0
    ReputationRep:
    (Original post by tozhan)
    you heat with the lid off on gentle heat to let the gases escape.

    you heat on full heat wit the lid on to avoid getting bits everywhere if it were to explode due to air trapped inside rapidly expanding. Also, if you want to stop your sample reacting with the atmosphere.

    you weigh your sample with the lid ON because the warm vapours set up convection currents above your sample and cause fluctuations in your measurments.
    you have officially confused the crap out of me.
    so..
    weigh with lid on
    full heat with lid on then every now and then turn the heat down and take the lid off?
    then after weigh with the lid on?

    do you have to wait for the crucible to cool?
    Offline

    17
    ReputationRep:
    (Original post by mengzor)
    you have officially confused the crap out of me.
    so..
    weigh with lid on
    full heat with lid on then every now and then turn the heat down and take the lid off?
    then after weigh with the lid on?

    do you have to wait for the crucible to cool?
    I think its:
    1: Weigh with lid on
    2: Heat with lid on UNTIL the compound is as hot as its gonna go, so that its stopped expanding and will no longer spit bits everywhere
    3: Continue the process without the lid, because the water of crystallisation needs to escape so that it will show up as a difference in mass when you weigh it finally.
    4: Weigh with lid (because you weighed with lid to start with)
    Better?
    Offline

    5
    ReputationRep:
    precisely! and
    5.repeat from step 4 until you get two successive results...
    and YES... you have to wait for the crucible to cool down before you weigh it... otherwise, you will get an inaccurate reading! hope that helped!
    Offline

    5
    ReputationRep:
    (Original post by suzukiescudo)
    what have people written about the risk assesment?
    just the same old rubbish! lol... wear lab coat... wear gloves because its irritant and so on...
    Offline

    0
    ReputationRep:
    (Original post by Coolraj)
    precisely! and
    and YES... you have to wait for the crucible to cool down before you weigh it...
    in a lab experiment this might be possible. but the reason for weighing with the lid on is because in an exam condition you would not have time to let it cool down. so you leave the lid on to avoid convection currents. This was in last years practical and was the only thing i couldnt answer. i later found out from the mark scheme...
    Offline

    0
    ReputationRep:
    what would be a good amount of Na2CO3 for each experiment?

    like... 2grams? 1.5?
    Offline

    0
    ReputationRep:
    wth is risk assessment?
    is that areas that you could mess up the experiment?
    Offline

    0
    ReputationRep:
    the more you use the better as then inaccuracies will be kept to a minimum.

    dont use so much that you cant fit it in the crucible!

    other than that its up to you.... 2 g might be ok. your choice
    Offline

    17
    ReputationRep:
    (Original post by tozhan)
    in a lab experiment this might be possible. but the reason for weighing with the lid on is because in an exam condition you would not have time to let it cool down. so you leave the lid on to avoid convection currents. This was in last years practical and was the only thing i couldnt answer. i later found out from the mark scheme...
    and of course, that Kevlar bodyarmour!!!
    Offline

    0
    ReputationRep:
    can someone help!
    in my intro ive written about sodium. meltin point, ionisation enery etc.
    what can i write after....
    its in tomoro....stressin!!!
    Offline

    17
    ReputationRep:
    (Original post by suzukiescudo)
    can someone help!
    in my intro ive written about sodium. meltin point, ionisation enery etc.
    what can i write after....
    its in tomoro....stressin!!!
    Bonding between water of crystallisation and the molecule. Bonding between carbonate ion and sodium. You can't need more than that.. its just the intro! Surely you've run out of words... the planning's the important thing.
    Also.. your teacher should be able to suggest amendments. You're only officially having it given over to OCR on the day of the practical. (although your lecturers will require it handed in before that, unless you're lucky and you go to my college.)
    Offline

    0
    ReputationRep:
    Also.. your teacher should be able to suggest amendments.
    i cant i go to evening classes at that crappy college!

    have you got a website for water of crystallisation?
    Offline

    0
    ReputationRep:
    thanx
    Offline

    0
    ReputationRep:
    sorry to bother again..
    how do you carry out the specimen calculation to show the number of moles of water of crystallisation would be calculated from the first experiment.
    this is the 1 with the crucible and the heating.
    Offline

    5
    ReputationRep:
    (Original post by suzukiescudo)
    sorry to bother again..
    how do you carry out the specimen calculation to show the number of moles of water of crystallisation would be calculated from the first experiment.
    this is the 1 with the crucible and the heating.
    make up the value you obtained from your experiment (even better if you did the pre. test)
    and using the formula moles = mass/mr, calculate the moles of water... should be stright foward! hope this helped
    Offline

    0
    ReputationRep:
    thankx once agian.
    is the risk assessment the same as the safety precautions?
    Offline

    5
    ReputationRep:
    (Original post by suzukiescudo)
    thankx once agian.
    is the risk assessment the same as the safety precautions?
    yep... just say all sort of rubbish stuff like wear lab coat and so on... i think there is another reply somewhere on this somewhere in this thread, which should be more helpful than my reply!
 
 
 
Turn on thread page Beta
Updated: April 6, 2008
Poll
Do you think parents should charge rent?

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.