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Author: Subject: Accuracy of cheap volumetric flasks ?
Sulaiman
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[*] posted on 6-3-2020 at 03:42
Accuracy of cheap volumetric flasks ?


I intend to buy a 100ml class A volumetric flask.
Pyrex : Bomex China = 5 : 1 cost ratio.
Anyone cheched the calibration accuracy of cheap Chinese volumetric flasks ?
Specifically I'm looking at
https://shopee.com.my/Pyrex-Volumetric-Flask-Class-A-Ready-S...
vs
https://shopee.com.my/Teamwinm-1pcs-100ml-Clear-Glass-Volume...

EDIT : reply to below comment by Ubya here to avoid bumping this thread......
____________________
That's pretty accurate !

I closed one eye and ordered the pyrex volumetric flask, to be reasonably confident of accuracy.
(local disctributor for scilabware=uk pyrex/quickfit, batch certificate available)

P.S. I have a selection of classA and classB volumetric flasks, packed in boxes, in uk.
I just want something to play with now (vs. my new balance),that will be useful later.

[Edited on 6-3-2020 by Sulaiman]




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Ubya
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[*] posted on 6-3-2020 at 04:17


well i haven't bought many volumetric flasks, i only bought a chinese 1ml one. i tested its accuracy using a milligram balance, after calibration and zeroing it i measured 1.000+-1mg





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Dr.Bob
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[*] posted on 6-3-2020 at 18:16


The effect of the temperature on the density and the glass volume is almost as much as any variation in glass manufacturing, unless they are just crap. The analytical chemists in my group tend to measure solvent by weight (using the known density of the solvent at a set temperature) if they are really needing accurate amounts. My compromise is that I tend to test a volumetric flask by filling to the line and weighting before and after to see if the actual weight matches the calulated weight. If so, then I just use the flask, if not, I can either find another flask or do it by weight. But for 99% of what I do, a simple volumetric flask (type A) does fine. We use them for opptical rotation samples, acid/base solutions when needed, and making standards for HPLC.

If anyone in the US wants cheap used Pyrex volumetrics I have lots, but it would cost a fortune to ship to the UK, sadly. I even have some brand new ones in small sizes.
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brubei
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[*] posted on 7-3-2020 at 01:48


Just ask to the seller what are the quality, certification (ISO) and measurement error associated with for the products.

Reliable sellers must know this parameters.

exemple of quality classification :
Quote:
Even Class A volumetric glassware is not absolute but rather has a tolerance from its stated nominal value. For example, a 25 mL Class A Transfer Volumetric Pipet has a capacity tolerance of ± 0.03 mL, and a 50 mL Class A Buret has a tolerance of ±0.05 mL at full capacity.


https://www.sigmaaldrich.com/content/dam/sigma-aldrich/count...




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Sulaiman
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[*] posted on 7-3-2020 at 02:13


Quote: Originally posted by Dr.Bob  
... The analytical chemists in my group tend to measure solvent by weight (using the known density of the solvent at a set temperature) if they are really needing accurate amounts...

I agree that for accuracy chemicals/solvents/reactants are best measured by weight.

In this case I intend to do some density measurements so this 100 +/- 0.08 ml volumetric flask will be my reference for volume.
I would have prefered a larger size as the relative accuracy of volumetric flasks increases with increasing capacity,
but I'm limited by my balance to 220g max.




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[*] posted on 7-3-2020 at 04:23


As long as the glass is stable (and I expect it would be), you can calibrate it yourself using a balance.
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Sulaiman
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[*] posted on 12-3-2020 at 22:21


my first intention is to measure the density of water as accurately as I can :)
(tap/rain/distilled, 'as-is'/boiled = six results)
I hope that the limitations to the accuracy will be ;
. temperature dependant corrections for water density and air density
. the accuracy of the volumetric flask
. weighing errors (c1mg ... when I'm patient)
and not just ;
. my techniques
______________________________________________________________
I downloaded the batch certificate for the volumetric flask ;
Attachment: 100ML.pdf (671kB)
This file has been downloaded 24 times
If on the day of production the average was 100.021ml with std.dev. of 0.014ml,
can I confidently report the capacity (at 20oC) to be 100.021 ml +/-0.014ml ?

[Edited on 13-3-2020 by Sulaiman]




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