posted by Hunter .
How would you prepare a 25.0% water in ethyl alcohol solution using 100.0 ml of ethyl alcohol (The density of ethyl alcohol is 0.7893 g/ml)
Is that 25.0% w/w H2O in ethanol? I will assume so.
Assuming water and alcohol volumes are additive (actually they do not)
100 mL ethanol has a mass of m = v*d = 100 x 0.789 = 78.9g ethanol.
Since % is g/100 g soln, that will be
(x/78.9 EtOH + 21.1 H2O) = 0.25
Therefore, x = 0.25g H2O.
We mix 0.25g H2O in 100 mL H2O and we will have 25%.
[0.25g H2O/(100 g soln)]*100 = 25% w/w.