Question

How much 100% ethanol would someone need to make 100 mL of a 70% alcohol?

Please show all work. Thanks.

Answer 1

70% alcohol means;

In the 100 mL solution, 70 mL of alcohol and 30 mL of other solvents (water).

So,

70% (100 mL of E) + 30%(100mL of W) = 100 mL (total liquid mixed) [where E = ethanol and W = water].

Therefore, you need:

0.7 x 100 mL = 70 mL of ethanol
0.3 x 100 mL = 30 mL of water

OR

You have to dilute the alchohol solution.
Using the dilution equation,
C1V1=C2V2
70 x 100 = 100 x V2
V2 = 70 ml
You have to take 70 mL from the 100% alcohol solution and add water until it becomes 100 mL.