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Question Recrystallisation

7 years 9 months ago #19840 by monkapotamus
Anyone know of a good alternative (i.e less messy) to the salol experiment for showing the difference in recrystallising times at different temperatures?
Thanks

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7 years 9 months ago #19842 by Marcus Rowland
Salol is actually pretty good in that respect, since you can clear it up easily with hot water and all of the glassware will come clean at ordinary dish-washer temperatures - a lot of the others are much harder to shift. It's also relatively cheap and safe to handle, which are big pluses for this sort of thing.

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7 years 9 months ago #19845 by Baldilocks
I don't clear up the salol, I just keep a set of boiling tubes with it in for that purpose.

“Do not believe everything you read on the Internet.” -Abraham Lincoln

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7 years 9 months ago #19861 by Annie

Marcus Rowland wrote: Salol is actually pretty good in that respect, since you can clear it up easily with hot water and all of the glassware will come clean at ordinary dish-washer temperatures - a lot of the others are much harder to shift. It's also relatively cheap and safe to handle, which are big pluses for this sort of thing.


Try simply soaking the glassware in cold soapy water rather than hot. The salol sort of slides off the glass then you remove the glass & rinse.

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7 years 8 months ago #19909 by Jules
I concur with Baldilocks on this - don't wash up, just re-use! easy and eco-friendly!

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7 years 8 months ago #19924 by Annie

Jules wrote: I concur with Baldilocks on this - don't wash up, just re-use! easy and eco-friendly!

yep, me too regarding the boiling tubes, but you cant reuse the glass slides it is blobbed on unless you wash 'em. ( our lot like to look at the different crystal formations under a microscope, though I am aware you could use a hand lens)

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7 years 8 months ago #19929 by Marcus Rowland

Annie wrote:

Jules wrote: I concur with Baldilocks on this - don't wash up, just re-use! easy and eco-friendly!

yep, me too regarding the boiling tubes, but you cant reuse the glass slides it is blobbed on unless you wash 'em. ( our lot like to look at the different crystal formations under a microscope, though I am aware you could use a hand lens)

Exactly - and someone always gets some into a beaker or spills it on a desk.

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7 years 8 months ago #19930 by Cookaburra
If this is to show that fast cooling produces smaller crystals, we use benzoic acid for this. They dissolve benzoic acid in two boiling tubes placed in a hot water bath when dissolved one is placed at room temp and the other cooled rapidly under a running tap. there is quite a marked difference. and afterwards I filter the crystals out, dry them and reuse.
The following user(s) said Thank You: monkapotamus, Baldilocks

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6 months 1 week ago #41372 by Doolally
quick question - a Google search gives melting point of benzoic acid as 123oC. So presumably this is a beaker on a tripod kind of water bath. Does this cause any issues when they are lifting the boiling tubes out?

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6 months 1 week ago #41374 by prep_room_boy

Doolally wrote: quick question - a Google search gives melting point of benzoic acid as 123oC. So presumably this is a beaker on a tripod kind of water bath.



Beaker with a water bath will only give 100oC, so not enough to melt it.


I always used Salol and kept a dedicated set of tubes for it, slides were binned after use as it was more cost effective than the time spent trying to clean them.


I still miss the smell of hot Naptha, but not the hassle that came with it.
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6 months 1 week ago #41376 by Doolally
ooops! Can tell my brain's already in holiday mode

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6 months 1 week ago #41377 by Cookaburra
The Benzoic acid doesn't melt, it dissolves, but it is only sparingly soluble in boiling water. When it comes out of solution the size and shape of the crystals depends on the speed of cooling. I used to filter the crystals out of the tubes and reuse them.
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