Biology Question

Question

How much milliliters of absolute ethanol (100% ethanol) would you mix with how much milliliter of pure water to make 100ml of 70% (v/v) ethanol solution ?

Answer 1

V1C1 = V2C2

V1 = volume 1 = x ml

C1 = concentration 1 = 100%

V2 = volume 2 = 100 ml

C2 = concentration 2 = 70%

(x ml)(100%) = (100 ml)(70%)

x = 70 ml of 100% ethanol should be mixed with 30 ml of pure water. However, this assumes that the volumes are additive, i.e. that 70 ml ethanol + 30 ml water = 100 mls. This is not likely to be the case, but in many introductory chemistry courses, they assume it is.

Answer 2

(v/v) % = volume of solute/ volume of solution.

70 % = x / 100 mL

x = 70 mL of ethanol