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Why 70% ethanol & not 95% as disinfectant? - (Jun/12/2006 )

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This depends on the chemical structure of methanol molecules : CH3-CH2OH
Two methanol molecules make two hydrogenic bands with one
H2O molecule. that is:

CH3-CH2OH ----- H-O-H ----- OHCH2-CH3

That is we need One third(33%) H2O and Two third(66%~~70%) methanol
for Full-Dehydration of methanol molecules.
from IRAN


Hi again

When I was a high school student (I am MSc now and looking forward to finding a PhD degree position in USA or Canada) , I have read in chemistry class that the hydrogen bans between Water-Alcohol is stronger than Water-Water and Alcohol-Alcohol .

So this strong bands decreases the speed of evaporation Alcohol.


QUOTE (Dodo @ Jun 12 2006, 06:59 AM)
Hiya all, as a newbie here, allow me to greet u all. Hellooooo!!! I have a question which trouble me quite a long time. Why ethanol 70% is always used as disinfectant and not 95% o any other %? Can anyone help me in this question? Coz every manual i search so far just say 70% without any explaination.

Hi newbie.... 70% ethanol is very commonly used as a disinfectant in labs.. 70% is enough to kill bacteria or other comtaminants on the workbench...... Ethanol is also flammable so..the concentration % should not be so high... Bleach also can be used but still the common one is 70% ethanol.

-Gomes Nicholas-

QUOTE (Missele @ Jun 12 2006, 07:33 AM)
because you need also water to denature the proteins, enough water but not too much, not to dilute ethanol. That's why 70% is the best concentration to use, and it is better than 90%.

it is just like you need shower foam + water to clean yourself when to take bath. detergent alone cannot do the work well.


QUOTE (dersven @ Aug 22 2006, 11:57 AM)
Look at:

Hugo, 1971 (he said: "vegetative cells stay alive for 24h in 96")
Wallhäuser & Schmidt, 1967 (they said: "bacillus spores stay alive for 3 month in EtOH")

If you habe access to the papers, i'm interested to get them.


95% EtOH can denature the protein outside the bacteria only and can not kill them,
but 70% EtOH will permeate into bacteria, kill them furtherly. that is my opinion which i hope will give you some clue.


QUOTE (Champ @ Jul 9 2006, 09:29 AM)
yes the only reason is 95% alcohol vapourizes quickly,
for relatively longer time 70% is est suited.....

yes i've been told that too from the TA that 95% alcohol vaporizes i guess that's the most probably explanation...

-Property of Yulia-

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