Answer:
For example, to make 70% ethanol from 95% ethanol, take 70 mL of 95% ethanol and add enough water to bring the volume to 95 mL. You will then have 95 mL of 70% ethanol. This works for any dilution and all that is required is a large enough graduated cylinder.
When using liquid reagents, the percent concentration is based upon volume per volume, i.e. #ml/100ml. Example 2: If one wished to make a 70% ethanol solution, 70 ml of 100% ethanol would be dissolved in 30 ml of water (or the equivalent for whatever volume was needed).
