jamit
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volumetric flasks and pipettes
I just acquired some volumetric flasks and pipettes... so I checked the search engine and found nothing...zero. wow!
Does anyone here use them in their home lab to make molar solutions? Or is the use of precision pipettes or volumetric flask useless (or
non-essential) for most home experimenters?
I also found cleaning them such a pain because of the small neck or tube.
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SulfurApothecary
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To clean them take some rice and water and put it in the volumetric flask, shake for a couple minutes and pour out the stuff and rinse it. I make
molar solutions, but not a whole lot, if you look at the video of my home lab you can see I have 5 volumetric flasks, this is overkill for the average
experimenter (unless analytical) but if you like very exact measurements, its good.
You can't arrest me, it was for science!
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Fossil
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If rice water doesn't work, try conc fuming HCl for organic matter. It always works for me.
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Hexavalent
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Rice water?
I attest to Fossil about the organic matter, and failing that a soak in hot water or an organic solvent seems to work. NaCl and acetone (the salt is
insoluble), when shaken inside a dirty flask, are very effective also, as is boiling water with some sand in the bottom of the flask.
For your pipettes, just use your pump to repeatedly draw your cleaning solution through the pipette...you can also stand them upright, submerged in
warm,soapy water, in a 3-4L erlenmeyer.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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edgecase
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I don't think it's a good idea to use sand, there is silica in there which is the same substance and hardness as glass... and therefore can scratch
it. I made that mistake once.
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SulfurApothecary
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I meant rice and water not "rice water". The rice bangs against the sides of the glass and knocks off anything in there, while the water carries it or
dissolves the compound inside. This has worked very well for me in the past.
You can't arrest me, it was for science!
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Endimion17
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It won't scratch anything if it's sea sand (round particles) and you just boil the water with them inside for a short time.
Do we really need another thread on cleaning glassware? We just had one less than a month ago. Everything one needs to know has already been discussed
ad nauseam.
Regarding the flasks and pipettes, they are essential for anything above elementary school chemistry. Every home experimenter should own at least one
volumetric flask and 2-3 pipettes of different volumes.
I recommend 100 ml flasks and 1, 5, 10 ml pipettes. Not only they're useful for making standardized solutions, but by using them you gain a sense of
accuracy and precision, qualities that many home experimenters lack.
Back when I was starting this as a kid, there were no Internet stores and you couldn't just buy these things, not even at a pharmacist. Flasks,
pipettes, any precise scales, all that was out of the reach. Now, these things are everywhere and widely available. Use that opportunity and buy a
nice set.
A nice upgrade is a burette. Sometimes they're not very expensive.
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Hexavalent
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I got my 50x0.1ml burette from my teacher gratis; the top had chipped ever so slightly and was now considered 'a safety issue to use in the school'. I
have 1ml, 2ml, 5ml and 10ml Mohr pipettes and 5ml and 10ml proper volumetric pipettes, obtained from someone who ran an advertisement in a local
newspaper about glassware and also from my teacher, this time because they were excess stock and old. I have x3 100ml volumetric flasks, x1 500ml
flask and x1 1L flask. I clean each of these items of glassware every month with the following:
a) soap and water
b) tap water
c) hydrochloric acid, 20%
d) tap water
d) acetone
e) tap water
e) soap and tap water
f) tap water
g) distilled water
h) acetone
in that order.
Probably overkill, but it sure keeps my glassware, which I revere and only use for analytical purposes, very clean and ready to use. Everything is
stored in a cabinet, often with some parafilm or cling-film over the top, and the pipettes have their own special rack that I made from scrap
materials.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Endimion17
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It is an overkill. 
Soap and water are used when chromic acid is too much to handle, and it usually works. HCl can be used after it. Rinse with tap water and then with
distilled water. That's enough, unless your burette has been in a tar pit for several years.
The last rinse should always be distilled water. Those are the rules, and they're based on logic and experience.
Acetone contains greasy stuff. Even traces are enough to ruin that soap and water wash.
After washing, open to stopcock and place the burette vertically, neck down.
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Fossil
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Spongy wet rice wont knock anything off anything.
Quote: Originally posted by SulfurApothecary  | | I meant rice and water not "rice water". The rice bangs against the sides of the glass and knocks off anything in there, while the water carries it or
dissolves the compound inside. This has worked very well for me in the past. |
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Hexavalent
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I was always told never to do this, as some of the grease from the stopcock can make its way into the glass bit, distorting menisci and giving
incorrect values for analytical work. At school, we clean the burettes and then put them the right way up in a special rack. The tops are covered with
Parafilm to stop dust and fine particles from settling in them.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Mildronate
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I use abrasive pasta + water + this (i dont know english name for it): http://prana-ko.lv/index.php?categoryID=638, for pipete i use smoking pipe cleaners, sometimes dichromate +h2sO4, acetone.
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Hexavalent
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Do you mean a bottle brush?
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Endimion17
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| Quote: Originally posted by Hexavalent | | I was always told never to do this, as some of the grease from the stopcock can make its way into the glass bit, distorting menisci and giving
incorrect values for analytical work. At school, we clean the burettes and then put them the right way up in a special rack. The tops are covered with
Parafilm to stop dust and fine particles from settling in them. |
Yes, that happens if someone puts a ton of grease inside. Properly greased stopcocks do not leech grease. It is impossible. PTFE stopcocks don't even
need grease, and the most burettes are modern ones, with teflon.
Opened stopcock and vertical placement are employed to ensure thorough drying.
That's a neat way to quickly fuck up volumetric glassware.
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Mildronate
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