I have a bottle of 95% ethanol purchased from the manufacturer.

Question

Normally, when it is not stated, does it mean 95% w/w ethanol?

I need to prepare 100ml of 40% v/v ethanol solution from 95% ethanol.
Please show me the calculation steps.

Thanks.

Answer 1

when not stated, 95% is v/v

you want to dilute the ethanol 95/45 times, or 2.111 times. THat means one part alcohol, and 1.111 parts water.

100ml/2.111=47.37 is a part.
so, 47.37 ml of 95%
52.63 ml of water.