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JoeyHK
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#21
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#21
(Original post by chigs)
my m8 sed summin about using oil to heat the reactants coz u need 2 get it 2 110 degrees. i think it was at the back of the "make the grade" revision guide........................ i messed up that paper

oooooooooooo........i just directly heat the mixture, i haven't thought about the oil bath.............
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ravs
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#22
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#22
yeah and when added to the mixture it goes purple to colourless, then fait pink at endpoint
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qqqwwweee
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#23
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#23
(Original post by ravs)
yeah and when added to the mixture it goes purple to colourless, then fait pink at endpoint
That's what I wrote
There are 3 marks right?
I also mentioned the colourless bubbles of oxygen. but i dont know whether it can be observed
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me...
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#24
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#24
(Original post by JoeyHK)
The max. temp. of water bath is 100 oC, right? But the boiling point of the bezene is over 100 oC, how can you use the water bath?
oh yeh.... doh ... damn...
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qqqwwweee
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#25
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#25
(Original post by zxcvbnm)
doesnt it go yellow/orange during addition and then goes pink at end point i am sure i have read it somewhere
there are no ions causing the yellow/orange colour.
I think you mix it up the acid-base titration using methyl orange as the indicator
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infekt
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#26
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#26
for 3 marks
(1)during the reaction u see bubbles of colourless gas or a colourless gas is given of ... either is rite
KMno4 turns from purple(1) to colourless(1) or light pink at the end point (pratically its light pink ... but in the books its says colourless )
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Mel_R
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#27
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#27
hi
i'm nu to this

yeah i did pretty much the same thing - used KMnO4 in burette, and reflux set-up for that other question

don't worry about it now: it's pretty much too late! best to just concentrate on next paper!
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visesh
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#28
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#28
(Original post by keisiuho)
That's what I wrote
There are 3 marks right?
I also mentioned the colourless bubbles of oxygen. but i dont know whether it can be observed
i wrote that too

it should be seen, cos its bubbles! lol

also magenta to pale pink, (colourless only if excess is added)

that should make 3 marks
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infekt
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#29
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#29
i think kmno4 was in the conical flask .. wasnt it ?? ... coz otherwise u wouldnt see n e colour change apart from mayb colourless to pink .. in whi9ch caseim screwed
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[_Z_]
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#30
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#30
Kmno4 is always kept in the burette... ( that was a question in one of the past papers)... and i read somewhere... that in acidic medium ( as was given in the question)... the colour changes from pink/purple to green..... and in non acidic medium to colourless.not sure bout that though.
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zxcvbnm
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#31
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#31
in my notes i have written down that kmno4 changes to purple to colourless but due to redox processes and air partilces etc it is seen as a vvvv pale colour during addition and than persists a pink color at end point
i am not sure if this is right?
any 1 has any ideas
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qqqwwweee
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#32
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#32
(Original post by zxcvbnm)
in my notes i have written down that kmno4 changes to purple to colourless but due to redox processes and air partilces etc it is seen as a vvvv pale colour during addition and than persists a pink color at end point
i am not sure if this is right?
any 1 has any ideas
Actually it is very very pale pink. Practically what you can observe is colourless.
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qqqwwweee
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#33
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#33
(Original post by infekt)
i think kmno4 was in the conical flask .. wasnt it ?? ... coz otherwise u wouldnt see n e colour change apart from mayb colourless to pink .. in whi9ch caseim screwed
If A is titrated with B, A is in the conical flask and B in burette
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qqqwwweee
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#34
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#34
(Original post by JoeyHK)
oooooooooooo........i just directly heat the mixture, i haven't thought about the oil bath.............
In HKAL, at least two marks are awarded to a drawing of a reflux condenser including one for "water in and water out".

But GCE only gives you one mark for this stuff and a suitable heating source is often worth a mark.

In this case, a heating mantle or an oil bath is the appropriate choice
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