Sulaiman
International Hazard
Posts: 3558
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Offline
|
|
Maximum temperature for a Volumetric Flask
I have a Pyrex 100ml Class-A / USP volumetric flask,
the basic accuracy is +/-0.08ml
but the batch certificate is 100.02ml +/-0.014ml (1 std.Dev.)
Getting it thoroughly dry, to return it to its tare weight of 68.8072g (with stopper) is tedious
(wash and rinse with water, rinse with acetone, wait for residual acetone to evaporate, blow air to remove acetone vapour)
Would heating the flask to e.g. 120oC in an oven to dry it, significantly affect its calibration ?
CAUTION : Hobby Chemist, not Professional or even Amateur
|
|
|
ArbuzToWoda
Hazard to Self
Posts: 98
Registered: 15-7-2020
Member Is Offline
|
|
These sites explain why it's best not to heat volumetric flasks:
https://chemistry.stackexchange.com/questions/9665/why-are-w...
http://faculty.sites.uci.edu/chem1l/files/2013/11/RDGvolflas...
If you're concerned about the precision so much that you calibrate your flasks to the 3rd (edit: 4th) decimal place then you shouldn't heat it up...
although I do doubt that it could change it's volume that significantly.
[Edited on 31-8-2020 by ArbuzToWoda]
|
|
|
unionised
International Hazard
Posts: 5102
Registered: 1-11-2003
Location: UK
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by ArbuzToWoda  |
If you're concerned about the precision so much that you calibrate your flasks to the 3rd (edit: 4th) decimal place ...
[Edited on 31-8-2020 by ArbuzToWoda] |
All the volumetric flasks I have seen have been calibrated to the 6th decimal place* or better, some to the 9th place
Very few were calibrated to more than 3 significant figures.
*if one works in tonnes.
|
|
|
Sulaiman
International Hazard
Posts: 3558
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Offline
|
|
Its my current mini-obsession - trying to get textbook values for the density of water to 4 significant digits.
So far I always get results less than textbook.
(after balance re-cal, temperature and buoyancy compensations and using freshly boiled distilled water)
Complete overkill for general chemistry, just a personal challenge.
Even filling the volumetric flask to the calibration line and getting consistent results is challenging me.
CAUTION : Hobby Chemist, not Professional or even Amateur
|
|
|
unionised
International Hazard
Posts: 5102
Registered: 1-11-2003
Location: UK
Member Is Offline
Mood: No Mood
|
|
Are you remembering to account for air buoyancy?
|
|
|
Herr Haber
International Hazard
Posts: 1236
Registered: 29-1-2016
Member Is Offline
Mood: No Mood
|
|
If it can be autoclaved it can certainly withstand 120 degrees without losing accuracy.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
|
|
|
Sulaiman
International Hazard
Posts: 3558
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Offline
|
|
Yes, but so far only at nominal 1.2 mg/cm3,
Next is to compensate the buoyancy compensation for air temperature and pressure.
My measurements now generally match textbook values to 3 significant figures,
Its the fourth digit that eludes me.
Theoretically my limit to accuracy should be the volumetric flask uncertainty = fourth digit +/-1.4
Not vitally important for me to succeed, just trying has improved my techniques.
CAUTION : Hobby Chemist, not Professional or even Amateur
|
|
|
arkoma
Redneck Overlord
Posts: 1761
Registered: 3-2-2014
Location: On a Big Blue Marble hurtling through space
Member Is Offline
Mood: украї́нська
|
|
| Quote: | (Volumetric apparatus should not be heated: after washing
it is rinsed with acetone, then pure diethyl ether, and air-dried. Prior to use, equipment can be rinsed with acetone,
then with petroleum ether or pure diethyl ether, to remove the last traces of contaminants.) |
From "purification of laboratory Chemicals",6th Edition,page 3
"We believe the knowledge and cultural heritage of mankind should be accessible to all people around the world, regardless of their wealth, social
status, nationality, citizenship, etc" z-lib
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
