Yttrium2
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Accurate Volumetric Measurement
I've heard that the most accurate, (or is the term precise?) way to measure something is to use the vessel that has the same volume as what you want
the final volume of your solution to be.
In other words, to measure 800mls of liquid, it would be more accurate to use a 1000ml beaker, than to repeatedly use a syringe, or graduated
cylinder.
I'm wondering why this is if there is a higher standard deviation in the large container? There is insn't there?
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DavidJR
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Precision and accuracy are two very different things!
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markx
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Quote: Originally posted by Yttrium2  | I've heard that the most accurate, (or is the term precise?) way to measure something is to use the vessel that has the same volume as what you want
the final volume of your solution to be.
In other words, to measure 800mls of liquid, it would be more accurate to use a 1000ml beaker, than to repeatedly use a syringe, or graduated
cylinder.
I'm wondering why this is if there is a higher standard deviation in the large container? There is insn't there? |
A basic plunge into the theory of metrology and measurement uncertainty shall perhaps clarify the situation (or make it even more confusing at first
glance)  :
https://metrology.wordpress.com/statistical-methods-index/ba...
But a quick and simple cognitive explanation would be that measurement error and final uncertainty are composed of several individual components that
are all summed up in the "measurement model".
So when you use a single container with a known error, your measurement model shall contain the error of the container and the parallactic visual
error you make by assessing the fluid level (in a simple case).
When you use a syringe to measure that volume you encounter the same parallactic error+ syringe error every time you measure a portion of the volume
and that shall sum up in the final uncertainty increasing it.
But since the actual errors are impossible to measure and are rather assessed by a statictical random distribution theory, the final error may not
actually be greater than that achieved by the single container method.....just the uncertainty shall be greater. In other word you have less proven
credible confidence in the result...
Exact science is a figment of imagination.......
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zed
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Darned if I know.
New equipment has evolved.
I've always been kind of an approximator.
We used to make a big deal about this stuff.
The 1 liter graduated cylinder. https://www.ebay.com/itm/PYREX-3024-1L-Cylinder-Graduated-Si...
And the volumetric flask, were the standards when I was pupating. https://www.ebay.com/itm/PYREX-1L-1000mLClass-A-Lifetime-Red...
I gotta think the burette is more accurate than either. https://www.ebay.com/itm/Burette-with-Glass-Stopcock-100mL-C...
Fragile, and expensive; Burettes. Easy to break. I'd like to own some, but at the moment, I'm too cheap. Plus, shipping one seems like a recipe
for grief. I'll be unhappy when it arrives broken, and the supplier won't be happy when I don't want to pay.
Anyway, for my current purposes, I think syringes, PP measuring cups and graduated cylinders are probably close enough. Though I have the classy
glass stuff.
[Edited on 6-6-2018 by zed]
[Edited on 6-6-2018 by zed]
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