I have a bottle of 95% ethanol purchased from the manufacturer.
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.
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.
When it is not stated, it typically means that the concentration of ethanol is by volume. So, when you have a bottle of 95% ethanol, it usually refers to 95% v/v (volume/volume) ethanol.
To prepare a 100ml solution of 40% v/v ethanol from the 95% ethanol you have, you'll need to dilute it with a suitable amount of a diluent such as water. The formula you can use is:
%V1 x V1 = %V2 x V2
Where:
%V1 = initial concentration of ethanol (95%)
V1 = initial volume (unknown, since you want to find it)
%V2 = desired concentration of ethanol (40%)
V2 = final volume (100ml)
Let's solve for V1:
95% x V1 = 40% x 100ml
Multiply both sides of the equation by 100:
95V1 = 4000
Divide both sides by 95:
V1 = 4000 / 95
Therefore, V1 ≈ 42.11ml
So, you'll need to take approximately 42.11ml of the 95% ethanol and add water to make the total volume up to 100ml to obtain a 40% v/v ethanol solution.