### Description

The amount of water and 94.9% v/v ethanol required to make a diluted alcohol solution can be calculated using a simple formula and an alcoholometric table.

Parameters:

(1) specific gravity for the target dilution at 25°C

(2) target dilution as a percent vol/vol from 0 to 94.9%

volume of water in mL to add to 100 mL of 95% v/v ethanol =

= 100 * ((94.9 * ((specific gravity of target) / (percent target)) - 0.8096) =

= 9890 * ((specific gravity of target) / (percent target) - 80.96

where:

• Ethanol solutions may be expressed as volume to volume (v/v) or weight to volume (w/v).

• 94.9 is the percentage of the starting ethanol solution v/v.

• 0.8096 is the density of 94.9% v/v ethanol at 25°C.

• The specific gravity of the target solution needs to be read from an alcoholmetric table (which is given as a reference table in each edition of the USP). The data is from the National Bureau of Standards Bulletin, volume 9, pages 424-425.

final volume of solution in mL =

= (100 mL ethanol) + (X mL of water)

percent of solution that is water =

= 100% * (X mL water) / (100 mL + X mL)

To determine the volume of water and 94.9% ethanol to make Y mL of a dilute solution:

volume of 94.9% v/v ethanol =

= (target volume) * (100 - (percent of solution that is water)) / 100

volume of water =

= (target volume) * (percent of solution that is water) / 100