Sciencemadness Discussion Board

Most accurate volume measurement

nimbus8 - 12-6-2013 at 18:04

Hey everyone, before i buy a bunch of beakers and burets for my home lab would you guys recommend any way to measure volume that doesn't involve just eyeballing it. I know there are volume to weight conversion so you could like measure out a given number of grams of a substance to get a given volume.

I just want to be very precise when reacting come chemicals.

Crowfjord - 12-6-2013 at 18:57

I think most volumetric flasks, graduated cylinders and burets are accurate enough for hobby chemistry purposes, but if you have (or have access to) an analytical balance and an accurate thermometer, you can calibrate your volumetric glassware. Beakers and erlenmeyer flasks have marks for estimation only and shouldn't be used for volume measurement.

For example, I work for a lab that does quantitative analysis of elements in metals, and accuracy is a must. Before using new volumetric flasks, we need to verify their accuracy; some flasks are dead on, some need a new mark to show the actual level of the given volume. Assuming we want to calibrate a (clean and dry!) 100 ml volumetric flask, we tare it on the balance, then add deionized water (distilled is probably okay, too) whose temperature has been measured to one place past the decimal. Assuming the water is 20.0 degrees C, it had a density of 0.9982 g/mL*, so 100 mL has a mass of 99.82 g. This mass of water is added to the flask and a new mark is made at the bottom of the meniscus, or if the meniscus lies on the factory made mark, a scratch is made through the mark to indicate that it is correct.

*I got this value from a chart at work. Similar ones can probably be easily found online.

blogfast25 - 13-6-2013 at 03:01

Agreed, Crowfjord. For homelab work, even quantitative, most burettes and volumetric flasks should be accurate enough.

But:
Quote: Originally posted by Crowfjord  
Beakers and erlenmeyer flasks have marks for estimation only and shouldn't be used for volume measurement.



The marks on decent beakers and conical flasks are generally accurate enough for use in preparative recipes for instance.

ScienceSquirrel - 13-6-2013 at 13:04

I have a few Volac grade A 100ml pipettes and I have checked them against a scale accurate to 0.01g.
For the calibration of my hydrometers, this is accurate enough and I have convinced my local Customs of this.
I am allowed a bit of grace as the beers are bottle and barrel conditioned, so a little fermentation goes on in the final container providing condition.
I will mark a beer at 4.5% ABV when it goes out but it will be a bit sweet in the bottle so it will be about 4.6% if you store it away and allow the condition and flavours to develop.

blogfast25 - 13-6-2013 at 13:31

Quote: Originally posted by ScienceSquirrel  
I have a few Volac grade A 100ml pipettes and I have checked them against a scale accurate to 0.01g.
For the calibration of my hydrometers, this is accurate enough and I have convinced my local Customs of this.
I am allowed a bit of grace as the beers are bottle and barrel conditioned, so a little fermentation goes on in the final container providing condition.
I will mark a beer at 4.5% ABV when it goes out but it will be a bit sweet in the bottle so it will be about 4.6% if you store it away and allow the condition and flavours to develop.


You mean that using the verified pipettes you create water/alcohol mixtures of known alcohol ABV and use these standards to calibrate the hygrometers?

ScienceSquirrel - 13-6-2013 at 14:21

I test the pipettes against pure water and then against a sucrose solution of known gravity above the starting gravity of my beers, made up using sucrose and deionised water.
I do not need analytical results. Good enough is OK.

blogfast25 - 14-6-2013 at 04:09

Quote: Originally posted by ScienceSquirrel  
I test the pipettes against pure water and then against a sucrose solution of known gravity above the starting gravity of my beers, made up using sucrose and deionised water.
I do not need analytical results. Good enough is OK.



Got it. You assume conversion of sugars is complete. That's what I do to (and everyone else I assume). Will have to check my hydrometer once, that way.

There is no real easy analytical way to determine ABV.

Have you ever tried refractometry or is it inaccurate at about 5 % ABV?

ScienceSquirrel - 14-6-2013 at 04:20

Attenuation is about 70% with the final gravity being usually about 1.010 - 1.014 in a normal ale, although this can be as high as 1.016 - 1.020 in a barley wine.
http://www.fermentis.com/brewing/homebrewing/product-range/

Calculation of percentage alcohol by volume;

http://en.wikipedia.org/wiki/Alcohol_by_volume#Beer

Calibration of your hydrometer;

http://www.byo.com/stories/item/411-calibrate-your-hydromete...


[Edited on 14-6-2013 by ScienceSquirrel]

blogfast25 - 14-6-2013 at 04:56

Thanks for that.

Have you got a site dedicated to your microbrewery?

[Edited on 14-6-2013 by blogfast25]