[Nhcoll-l] Mixing EtOH, new question!

Fri Sep 9 18:09:00 EDT 2022

Now our conversation has touched on three effects resulting from mixing that all lead to density readings of recently mixed ethanol-water combinations indicating a higher ethanol concentration than the resulting homogenous and temperature equilibrated solutions would have:

  1.  Higher temperature leads to lower density leads to higher interpreted ethanol concentration (more true for simple hydrometers than digital density meters which indicate (and may account for) temperature.
  2.  Tiny gas bubble formation mostly from reduced solubility of gasses in the solution than in water (I think) but also from temperature increase.
  3.  Not all contraction-on-solution has been realized until dissolution is complete (measured density remains lower than final density until dissolution is complete.)
It is unfortunate that all these effects are in the same direction, leading to higher apparent ethanol concentrations. This reminds us of the importance of checking concentrations after sufficient mixing and elapsed time.
Rob

From: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu> On Behalf Of John E Simmons
Sent: Friday, September 9, 2022 5:34 PM
To: Simon Moore <couteaufin at btinternet.com>
Cc: NHCOLL-new <nhcoll-l at mailman.yale.edu>
Subject: Re: [Nhcoll-l] Mixing EtOH, new question!

Simon,
Good question. When I mixed ETOH in the carboy in the lab at Kansas the container became warm to the touch, but I never measured how much warmer. However, looking around the internet I found this:

https://sciencedemonstrations.fas.harvard.edu/presentations/mixing-ethanol-and-water

Mixing Ethanol and Water
Ethanol and water are mixed in volumetric glassware, showing a volume decrease and a temperature increase.

Two 250 ml graduated cylinders are filled to the line with water and ethanol (100%). A temperature probe shows both at room temperature. The temperature probe is then moved to an empty 500 ml graduated cylinder, and the contents of the two smaller cylinders poured simultaneously to mix well.

The temperature of the mixture rises about 8°C, and the volume decreases to 480 ml just after mixing, clearly visible on the scale of the 500 ml cylinder.

--John

On Wed, Sep 7, 2022 at 6:54 PM Simon Moore <couteaufin at btinternet.com<mailto:couteaufin at btinternet.com>> wrote:
This discussion has raised many interesting corollaries (many thanks Tonya, Rob, John and everyone else) - the temporary and partial re-separation of the alcohol mixture due to the physical properties of binary azeotropes, the argument about whether 70% or 80% alcohol is the best and what I have long wondered about - the enthalpy: temporary raising of temperature of the mixture.  I knew that this occurred but was told (long ago!) that it was about 0.00001 deg. C, almost negligible but enough to cause the air bubble release.

So my new question is - has anyone managed to measure or calculate for, say, 25 litres of alcohol being diluted to 70%, how many degrees would the temperature be raised?  I have never actually noticed it but I have been mixing 2.5 litre batches in glass bottles and never stopped to dip a thermometer in the mixture before and after mixing!

With all good wishes, Simon

Simon Moore MIScT, RSci, FLS, ACR
Conservator of Natural Sciences and Cutlery Historian,

www.natural-history-conservation.com<http://www.natural-history-conservation.com>

> On 7 Sep 2022, at 22:19, Andrew Stewart <AndrewS at tepapa.govt.nz<mailto:AndrewS at tepapa.govt.nz>> wrote:
>
> Hi Tonya,
>
> Yes, I used to have to decant and re-pour a dozen times to get the solution evenly mixed. Hardly ideal.
>
> Now we decant 70% ethanol from two 50 litre carboys on a trolley. The alcohol is pumped in first, then the water added as the pressure seems to get it right to the bottom. Then the home-made tool (we call the ‘super swizzler’) is plunged up & down several times to ensure everything is thoroughly mixed. The ‘wings’ are made of plastic cut from n icecream container J, and flex to get past the narrow mouth. The concentration is then checked and so far it seems to work.
>
> The larger black one for mixing alcohol in our 250 & 500 l tanks.
>
> Sometimes a home-made solution works just fine.
>
> Ngā mihi
> Andrew Stewart
>
> >><<<)o>
> Assistant Curator NE (Fishes)
> Museum of New Zealand
> 04 381 7314
> 027 7339363
>
>
>
>
> From: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu<mailto:nhcoll-l-bounces at mailman.yale.edu>> On Behalf Of Haff, Tonya (NCMI, Crace)
> Sent: Wednesday, 7 September 2022 1:40 PM
> To: nhcoll-l at mailman.yale.edu<mailto:nhcoll-l at mailman.yale.edu>
> Subject: [Nhcoll-l] Mixing EtOH
>
> Hello all,
>
> I have a question about mixing storage strength (70%) undenatured EtOH. Typically we add the correct proportions of 95% EtOH and water to a container and paddle or invert the container repeatedly to mix the liquids, and allow it to sit for ~24+ hrs. The containers we like best to use for dispensing 70% EtOH are 20L plastic water containers with a tap at the bottom. Recently we used our digital alcohol meter to test the alcohol concentration from the top and bottom (tap) of one of these containers and found the alcohol concentrations wildly different  - ~80% at the top and ~60% at the bottom – despite having been mixed more than 24 hours earlier. This makes me really concerned that we could be regularly using concentrations that are much above 70% with specimens. I wonder if any of you have had a similar problem, or if anyone can suggest a solution? Is there a better way of mixing or of ensuring the solution is properly combined? Any thoughts appreciated.
>
>
> Thank you!
>
> Cheers,
>
> Tonya
> -------------------------------------------------
> Dr. Tonya M. Haff
> Collection Manager
> Australian National Wildlife Collection
> CSIRO
> +61(0)419569109
> https://www.csiro.au/en/about/facilities-collections/collections/anwc
>
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NHCOLL-L is brought to you by the Society for the Preservation of
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