Calculation Examples
Alcohol Percentages
Pg 150
• If you have 96% ethanol on your shelf you
need to be able to dilute it doen to lower
percentages of alcohol for making up
potencies and dispensing. Any quantity of
any percentage alcohol can be lade by
applying the provided calculation:
X desired volume multiplied by X desired% ethanol = Y volume on hand multiplied by Y
% on hand
Example 1
• You have 96% ethanol (R-OH) on your shelf
• You want to make 200ml of 86% R-OH
• You need to know how much distilled water you
need to add to how much 96% R-OH to get
200ml of 86%
• Xvolume = 200ml
• X%
= 86%
• Y volume= ??
• Y%
= 96%
• Plug into the formula …………
Example 1
X desired volume multiplied by X desired% ethanol = Y volume on hand multiplied by Y
% on hand
200ml x 86%
17200
17200
96%
179.166
=
Yml x 96%
=
Yml x 96%
=
Yml
=
Yml
This means that you need to measure out 179ml of 96%
alcohol.
You want a volume of 200ml of 86% so you need to add
200ml – 179ml = 21ml of distilled water to 179ml of
96% R-OH to get 200ml of 86% R-OH
Example 2
• You have 86% ethanol (R-OH) on your shelf
• You want to make 70ml of 20% R-OH
• You need to know how much distilled water you
need to add to how much 86% R-OH to get 70ml
of 20%
• Xvolume
= 70ml
• X%
= 20%
• Y volume
= ??
• Y%
= 86%
• Plug into the formula …………
Example 2
X desired volume multiplied by X desired% ethanol = Y volume on hand multiplied by Y
% on hand
70ml x 20%
1400
1400
86%
16.279
=
Yml x 86%
=
Yml x 86%
=
Yml
=
Yml
This means that you need to measure out 16ml of
86% alcohol.
You want a volume of 70ml of 20% so you need to
add 70ml – 16ml = 54ml of distilled water to
16ml of 86% R-OH to get 70ml of 20% R-OH