Why 70% ethanol & not 95% as disinfectant? - (Jun/12/2006 )
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.
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.
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.
it is just like you need shower foam + water to clean yourself when to take bath. detergent alone cannot do the work well.
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.
for relatively longer time 70% is est suited.....
yes i've been told that too from the TA that 95% alcohol vaporizes faster...so i guess that's the most probably explanation...