NEMO-Chemistry
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Vacuum desicator..Another noob question
I have been looking at some preps and have seen mentioned drying things in a vacuum desiccator or in air for example at 40c.
What i want to know is how hard a vacumme do you need to pull in the desiccator? Normally i dont see this information given
The one that promted this question i misread and it isnt the one i thought it was but will do to illustrate what i mean.
The prep was for silver nitrite but i didnt have my glasses on and thought it was silver nitrate until i read the procedure  , anyway this is what it says
"Silver nitrite may be purified by recrystallization from water at 70° C, and is dried in a vacuum desiccator or in an air at about 40° C.
The yield of silver nitrite is about 90%, which is stored in a tightly-stoppered amber bottle."
So do you actually need to pull a vacuum or not in the desiccator? If you do then how much?
I dont own one yet but it's on my to get list, however i dont know how much of a vacuum you are meant to pull on them when drying? especially as there
would presumably be a desiccator in there as well.
Sorry for all the complete noob questions but i dont do chemistry at school and i have only done pretty basic chemistry so far, i have joined to try
and do more advanced things. I have done some reading but questions like this dont seem to be mentioned.
Cheers Nick
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BromicAcid
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If something specifies a vacuum desiccator then vacuum should be best available. What that means depends on your ability, I would shoot for 0.1 mmHg
or less. For some that is a decent vacuum, other unattainable, others would say I have a leak somewhere. But if it's not specified, best available.
In my experience, the desiccant (sulfuric acid, phosphorus pentoxide, magnesium perchlorate) usually is specified though. Vacuum desiccators are
messy, lots of grease, but they are a tool with a purpose and work well for drying solids that do not need heat. I'm always amused by older
references that may dry something in a dissector for months at a time. I wonder what mixture of patience, curiosity, and laziness it is at that
point.
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NEMO-Chemistry
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Quote: Originally posted by BromicAcid  | | If something specifies a vacuum desiccator then vacuum should be best available. What that means depends on your ability, I would shoot for 0.1 mmHg
or less. For some that is a decent vacuum, other unattainable, others would say I have a leak somewhere. But if it's not specified, best available.
In my experience, the desiccant (sulfuric acid, phosphorus pentoxide, magnesium perchlorate) usually is specified though. Vacuum desiccators are
messy, lots of grease, but they are a tool with a purpose and work well for drying solids that do not need heat. I'm always amused by older
references that may dry something in a dissector for months at a time. I wonder what mixture of patience, curiosity, and laziness it is at that
point. |
Thank you for the reply, I was going to use sodium hydroxide as the desiccant, I will try sulphuric acid when I get a desiccator. At the moment I use
a simple sealed plastic box and i cant pull a vacuum on that .
I have an old vacuum pump but no idea how much of a vacuum it will pull as i havnt needed to use it yet. It was going cheap at a car boot sale so i
got it a few weeks back (£5).
I thought seeing as it says you can dry in air at 40C then it wouldnt need much of a vacuum, but i wanted to check first.
This is a helpful site, i have lurked for a while then joined. I havnt done much yet but chemicals and glass take time to build up. I know alot of
people on here do amazing things with jam jars and all kinds of improvised things, but i have the kind of luck that would mean the jar would break
.
I decided to save up and slowly get the glass ware. My problem is the more i start to do the more i am enjoying it and wanting to do more!
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