Question

Question #8b4c4

Answer 1

This would depend on the total solution volume.

Explanation:

• First of all, you need to know how much you are preparing.
  I will assume 100 mL for convenience.
• Then we find the volume of ethanol and water:

70% = (volume of ethanol / total volume of solution) * 100%
0.7 = (volume of ethanol / total volume of solution)

Let
x = volume of ethanol
total volume = 100 mL

`0.7 = x/(100 mL) rarr x = 0.7 * 100mL`

x = 70 mL

`:.` volume of water = 100 mL - 70 mL = 30 mL

So in order to prepare 100 mL of 70% (v/v) ethanol solution, you need to add 70 mL of ethanol with 30 mL water.

If you have a different total volume in mind, simply change the total volume in the equation to your desired volume.

Additional Notes:
if you are in the laboratory, add 70 mL ethanol in a 100 mL volumetric flask and dilute to mark with water.