Calculation/measurement of concentration

[Pelson]

Hi there,

My first post here, but hopefully not my last.

I have a little question in how you can accurately measure or calculate the ABV of your alcohol.
I have a densimeter, but I really want to know the exact concentration of the alcohol I distilled.

By measuring the density (I took 10mL with a pipet, and weighted it on a little scale) I came to a density of 0.82 g/mL.
By way of a data chart I found on internet (http://www.separationprocesses.com/Cour ... erty01.htm) I guessed a wt% of about 89%.

But as ethanol-water isn't an ideal mixture, how can I calculate the vol% of it?

I tried several websites to maybe get partial molar volumes, or calculate them myself, but I can't seem to find the right way to do so.
I study chemistry, so actually I should be able to know the answer, but still... (maybe I should've payed more attention in class in stead of drawing stills).

Thanks for any tips.

[Braz]

Hi there,

My first post here, but hopefully not my last.

I have a little question in how you can accurately measure or calculate the ABV of your alcohol...

Thanks for any tips.

Use an alcohol proof & traile hydrometer. Inexpensive and accurate.

[rtalbigr]

Just get a proof hydrometer. Most brew shops have 'em or plenty of on-line stores. They're inexpensive, usually $6-10.

They'll give you a reading in either abv or proof.

Big R

[Pelson]

Hi guys,

I have a hydrometer, but the scale is 0-100 ABV...
I'll saw anotherone just now that goes from 70-100.. probably it'll be more accurate.

But still, apart from that. Isn't there some good way to really accurately calculate your abv?

(maybe it's just a personal thing... I really hate it when I can't solve chemical/mathematical issues myself)

Thanks anyway for the ideas!

[Prairiepiss]

Why do you need to know the exact measurement? What's easier the putting a hydrometer in and reading it?

[Pelson]

Just because...

I think I'm thought too well to try to measure things as correct as possible..
I know a hydrometer delivers a reasonably well approximation of the concentration, but still.. I kinda wanted to know an exact way.. (so you know you have for instance 94,564abv or so...)

Maybe I'll just have to take it to the lab in the university.. lol!

I'll just by myself a new, more accurate hydrometer and will try to satisfy my urge for exactness with that!

[rad14701]

Is this what you are looking for...???

Temperature & ABV Relationship Charts

With a properly equalized reflux column you can get a fairly accurate measurement of the %ABV in relation to the vapor temperature... Most here either use the charts or a parrots beak and alcometer...

[MudDuck]

Not really sure if this will help but check it out: http://www2.stetson.edu/~wgrubbs/datadr ... echen.html" onclick="window.open(this.href);return false;" rel="nofollow

[Dnderhead]

I dont thank going by weight is very accurate as what is mixed with alcohol can affect the outcome.
the guys in suits,distill,then measure alcohol after.thereby they can calculate ABV.

[Pelson]

Hi guys,

Thanks for the replies!

@ rad14701,
I allready saw this graph on the forum here, and didn't really know how i could use it. But indeed, if I just look at the temperature I take off the distillate it might be a really good approximation. Only problem is: my thermometer gave a verry constant temperature of something around 76°C... So i think I need to calibrate it first.. (I don't suppose it contained other stuff like methanol since it stayed between 76°-78°C for about 3 hours...)

@ MudDuck,
Also this page I studied.. I have a similar explanatian in a course of physical chemistry from the university, but It's just really difficult to calculate partial molar masses since they differ at different concentrations...

@ Dnderhead,
It is distilled alcohol, so only alcohol-water mixture.. if it wouldn't be like that, then off course you're wright that it wouldn't make any scense weighting it.

--> I'm also discussing this with some guys on a dutch chemistry forum (as I am from Belgium) and one guy over there also told me that, if the balance I use isn't that precise, the whole calculation just might not be that accurate either..
I also discussed the calculation from wt% to vol% over there, but without much result.
There's one guy suggesting this method (but I'm not convinced of the correctness of it...):

Take 1kg of the distillate, that gives 1.219L (density: 0.82g/mL)
In that there's 89 wt% EtOH so that makes 1.128L EtOH and 11wt% water which gives 0.110L water...

To go to the vol%, he then suggests to devide the volume EtOH by the total volume (1.128+.110=1.238) and so he gets a vol% of 91.11
Although the hydrometer gave something around 94% AND the total volume actually is 1.219L...

AAghrr.... I'm getting quite mad about this issue!
(hope you guys don't mind the metric units!)
SO... what do ya think?

[Bushman]

Take 1kg of the distillate, that gives 1.219L (density: 0.82g/mL)
In that there's 89 wt% EtOH so that makes 1.128L EtOH and 11wt% water which gives 0.110L water...

To go to the vol%, he then suggests to devide the volume EtOH by the total volume (1.128+.110=1.238) and so he gets a vol% of 91.11
Although the hydrometer gave something around 94% AND the total volume actually is 1.219L...

AAghrr.... I'm getting quite mad about this issue!
(hope you guys don't mind the metric units!)
SO... what do ya think?

Not sure I am doing this right but if I take 89% of 1.219L I get 1.08 not 1.128, if this is the case then 11% would be .134L if I subtract the two which would be the alcohol from the water I get the reading of 94.6% which is very close to the reading of the hydrometer.

[Pelson]

You're making a little mistake. You take the wt% (weight percentage) as vol% (volume percentage).

What I did was first calculating the volume of 1kg (by the density) wich gave 1.219L

Then I took a look at the parts (by weight) of alcohol and water. So 89% of 1kg of mixture is 890g EtOH.
With a density of 0.789g/mL that gives a volume of 1.128L (pure) alcohol.

For water you do the same: 110g of water is 110mL.

You see? You can't confuse the wt% with the vol%.. That's the hole issue I'm stuck with

[rad14701]

Just out of curiosity, why the spastic concern over the exact %ABV of your spirits to the point where trusting an alcometer isn't close enough...??? Seems a bit anal or perhaps too scientific for hobby distillation... What is the ulterior motive behind this endeavor...???

[Bushman]

OK, I see my mistake however I agree with Rad why so accurate temperature and purity will often have a marked influence so this could account for the difference.

[rtalbigr]

I can see the guy's point Rad. Knew an accoutant years ago who FREAKED over a penny in his checking account, spent hours tracking it down. Me, if I'm within 10 bucks I figure I'm good to go. Some guys are satisified with close, some guys need about 10 decimal points. To each his own .

Actually I think a very precise hydrometer and a very precise thermometer to make accurate temp corrections would give the most accurate results.

Big R

[rad14701]

I can see the guy's point Rad. Knew an accoutant years ago who FREAKED over a penny in his checking account, spent hours tracking it down. Me, if I'm within 10 bucks I figure I'm good to go. Some guys are satisified with close, some guys need about 10 decimal points. To each his own .

I have a customer who once paid me dearly to track down 11 cents she was off and couldn't find after searching herself for several days... Hundreds of dollars of my tome and hers for 11 cents, which I managed to find, that a simple adjustment entry would have resolved... I've done the same for her and other customers several more times over the years because they simply couldn't bring themselves to make that adjustment entry... Just plain crazy...

I understand how anal people can really be which was my reason for referencing it and wanting to know the why... Might not be more than a bizarre curiosity but we won't know until Pelson provides more insight...

[MudDuck]

I think this exercise may have more to do with the challenge of figuring out how to do it rather than any real need to do it, at any rate I think it's probably over my head.

[Pelson]

Hi guys...

Ok, big questions here about the why...

You're all 100% correct if you're saying: just buy an decent hydrometer. I know, that's just the easiest, and pretty accurate way of doing so.

But I've been studying chemistry for over 4 years now, and I've always learned to work as correct as possible. Also I've had tons of courses on concentration measurements, calculations, analitical chemistry... even quantum chemistry... So I just feel really stupid if I can't solve a riddle like this one.

It's just a plain simple question, how can I go from wt% to vol%... And I can't answer it... If you ask me how to measure a 1ppm (parts per million) concentration of a Strontium 87-88 ratio, that's no problem for me.. If you wanna know the molecular vibrations of toluene, I can calculate it.. But a simple (?) question like this one, I can't solve....

So I hope you understand why I'm just trying to understand the math behind it, and why I'm 'complaining about 1 penny instead of the whole bank'.. Just because I'm taught to think that way.
I have a whole bunch of lab-ware at my place at home, so I just wanted to be able to measure it myself, without hydrometer. But appearently it's just not that simple

Thanks for trying to help anyhow! It's been good discussing things whit you, and I'm looking forward to be helping someone on the forum here myself.

[Ayay]

When pot stillin the ABV is a guide. When reflux stillin the temp is a guide.

Like cookin a favourite dish on MasterChef. Comes down to how you can taste the difference, how you can present it, and ultimately how you can pull it off.

Guides are never 100% and interpreting the guides is up to you for final judgement in the harsh glare of reality TV .

[sterlingchap]

Get some absolute (99.999%) alcohol, and some pure distilled water.
Pipette exactly 50mls abs alcohol @20C into a tared (pre-weighed, weight empty = T) 100 ml volumetric flask.
Reweigh the flask = A
Fill to calibration mark with distilled water @20C.
Reweigh = F.
Weight of alcohol, Wa = A-T
Weight of water, Ww = F-A-T
Weight of alcohol + water, Wapw =F-T


Alcohol w/w% =100*Wa/(Wapw)
Alcohol w/v% = 100*Wa/100
Alcohol v/w%=100*50/(Wapw)
Alcohol v/v% = 100*50/100

Repeat the excercise using different volumes of alcohol and plot a graph. You will se it is non-linear.
Why?
Alcohol and water do not form "ideal" mixtures, due to molecular interactions between the components.
It is purely a relic of the ancient process of distillation (as are "proof" numbers) that Scotch bottles are labelled 40% vol alcohol, or 75 proof.
The good news is that I doubt many could taste the difference between 40% w/w, 40% w/v or 40% v/v alcohol. Even fewer would care about the difference after a few "testings"...... much more fun than - as the constipated mathematician said - "working it out with a pencil".


Chap

[rad14701]

Doesn't get much simpler than that...

I'll stick with an alcometer and thermometer and call things close enough... I don't need to know how and why the alcometer and thermometer work, I'm simply content that they do... Sometimes ignorance is bliss...

[Bushman]

I agree this post has almost run its course. I tried several times to solve the problem analytically but came to the conclusion there are too many variables to get an accurate reading!

[Pelson]

Allright...

I know, it's been a while, but I just wanted to tell you this:

I found a way of calculating my ABV's only by the density!
(it like suuuuperduupersimple....)

I actually made a program that runs on my TI-83 (graphic calculator).
I just make it insert a list of known density's from 1-100 Vol%, and then let it compare the measured density with the ones in the list.
After that, I'll just let it do a linear extrapolation in between the two points of known density.

(so if you have like a density of .8403, well, that's in between the densitye of 86° and 87°)

In this way I get a more precise measurment of my ABV without having to buy a new hydrometer
(i think, if I find a chart with half ABV's (like 86.5%) then it'll be even more correct!)

Maybe all of you allready thought of this, but hey, just wanted to tell you!

[Pelson]

And ow yeah:
Also found a way to solve the first question:

how to go from wt% to vol%=

wt%= mass(ethanol)/mass(total) = [Dens(ethanol)*Volume(Ethanol)]/[Dens(total)*Volume(total)] = [Dens(eth)/Dens(total)]*[Vol(eth)/vol(tot)] =
[0.789/Dens(total)]*Vol%

So brief:

Vol% = [Dens(tot)/0.789]*wt%

Neat huh?

[canadianmoonshiner]

I use a combination of proof & tralle alcometer & density to measue proof, quantity & blending water.

I check the temp corrected proof by alcometer, pour into volumetric flask & weigh to get density. Same result with both methods confirms result. Use tables ("Alcodens" software, TTB tables, etc) to weigh both alcohol & water for blending to bottling strength. Check by alcometer & density again to confirm result. Simple... x grams of x proof + x grams water = x mls @ x proof GOOD ENOUGH?