Hello,
I need to know at what temperature 50% ethanol boils at an altitude of 6000 m a.s.l. The air t could be around 7°C at that site. Does it behave the same as if it´s pure alcohol?
Water boils at 81°C at 6000 m in 7°C - atmospheric pressure should be 510.68 hPa and pure ethanol should boil at 61°C. Is that right? What is the boiling degree of 50:50 mixture?
At given altitude I have a pot full of boiling water (ca 81°C) and a stand inside which are immersed opened 10 ml test tubes full of 50% ethanol. Inside the test tubes are roots. The ethanol evaporates all the time, so, at the end (15 min boiling), there will be more water than 50:50. What interest me the most is if the content of the test tube is of the same temperature as that of the water around the test tubes in the pot or if it´s lower?
And how different would it be if the test tubes are capped and the ethanol could not evaporate? There will be higher pressure inside, but the boiling temperature of 50% ethanol should be higher then (Papin pot)? Or would it have the same t as the water around the test tubes?
I need to know the temperature, because I have to know if the enzymes in the roots are denatured at the end or not.
Thank you!
Zuzana
Article THE BOILING-POINT CURVE FOR MIXTURES OF ETHYL ALCOHOL AND WATER.
or, the slightly older:
https: //pubs.acs.org/doi/abs/10.1021/ja02033a004
[remove the spaces after https as the silly RG site wants to link to a 2002 rather than 1900 paper]
These show you the curve for BP v alcohol concentration.
The reduced pressure BP will be a drop from the mix. How much, is a challenge to calculate given the interraction of the water and ethanol and when an azeotrope really starts to kick in. I know, at 4% water there is a constant boiling miture with ethanol, so one can never distill to 100% ethanol.
This helps move you some way towards your answer, but not all the way.
Kind regards,
Rob
Hello Rob,
thank you for the answer and links! It´s been useful.
Yes, there are to many variables and uncertainities, for example the wind in the field that can be quite strong.
I´ll try to do an experiment with vacuum pump and barometer in lab. I´ll try to lower the atmospheric pressure to that of 6000 m and see what will happen with 50% ethanol boiled in the test tube.
Thank you, best regards!
Zuzana
Hello Zuzana,
Good idea to do an empirical test.
Two suggestions that I hope are helpful:
Use a wide diameter tube. If you use a regular lab tube the first bubbles of gas that form in the tube will probably case the mixture to be pushed out of the tube. A big round bottomed flask is probably best.
When the sample starts to boil, the vapour formed will cause the pressure to rise as the pump cannot take away all the vapour very fast. If you can borrow one a higher specification rotary evaporator would be useful, big flask and cold trap, plus vacuum source. If not, then some kind of cold trap, or freeze dryer, that you can connect between the pump and the tube will help collect the vapour and allow you to maintain a more constant pressure during boiling. I guess you will need a few minutes boiling under pressure to get a steady reading of temperature.
Would you be kind enough to share the result?
Best regards,
Rob
Hello Rob,
thanks for the suggestions! I´ll ask in the lab, if we have such things, but I think we won´t have the rotary evaporator, we are the Institute of Botany :) - ecologists. We have a lyophilizator, that´s a nice idea, I have to look if I can connect it somehow between the tube and boiled samples. And I´ll try it with the big flask.
From my experience, the mixture in the test tube evaporates quite quickly (probably also because of the wind) in the field. So the ratio towards the water raises quite fast, so the temperature also should rise more.
Thanks a lot, if there are any results, I´ll share them!
Best regards,
Zuzana
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