Diluting 950mL 99% Isopropyl Alcohol to 70%

To dilute 950mL of 99% Isopropyl Alcohol to 70%, add 1 2/3 cups water (distilled, if available).

DETAILS

Via Leslie Storer, high school science teacher:

To determine how much water to add to a specific volume of 99% isopropyl alcohol, use the dilution formula C1·V1 = C2·V2, where;

C1 = concentration before dilution

V1 = volume before dilution

C2 = concentration after dilution

V2 = volume after dilution

You should know all variables except V2. Solve the formula for V2:

V2 = C1·V1/C2

The amount of solvent to add is V2 - V1.

So:

(99% * 950mL) / 70% 

Results in 1344mL final volume (V2). 

The amount of water to add is 1344mL - 950mL, or 394mL, which equals 1.66534 cups water, or roughly 1 and 2/3 cups water.