Section 1: Dilutions of Ethanol



Ethanol comes as a 96 % v/v solution. You need to be able to prepare any concentration of Ethanol from this solution.



You should note that the preparation of some dilutions of Ethanol are described in the British Pharmacopeia 1988.



However, you will need to calculate how to prepare other concentrations as well and on the next few screens you can see how to do this.


NOTE: Ethanol (96 per cent) BP contains 96.0
to 96.6 % Ethanol giving an average of 96.3 %.


Comment on Preparing Ethanol Dilutions

When you dissolve Ethanol in water, there is

  1. an exothermic reaction and
  2. a significant contraction in the total volume.

Therefore when you are preparing dilutions of Ethanol, you mix the Ethanol and some water together and wait for the solution:

  1. to cool back down to 20 °C and
  2. finish contracting.
You then make up the final volume of the solution to that required.

You CAN NOT say what volume of water to mix with what volume of Ethanol; for example when making a 12 % v/v solution of Ethanol you can not say that you need 12 ml of Absolute Ethanol and 88 ml of water because the final volume - on mixing - of the solution would be less than 100 ml and the concentration would therefore be greater than 12 % v/v.

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The British Pharmacopeia lists the preparation of the following concentrations of Ethanol:
  1. 90 % 50 %
  2. 80 % 45 %
  3. 70 % 25 %
  4. 60 % 20 % Click Here For Example
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Example Dilution:
How to Prepare 20 % Ethanol

ETHANOL (20 PER CENT)
Alcohol (20 per cent)

Dilute 207 ml of Ethanol (96 per cent) to
1000 ml with Purified Water.

Content of ethanol 19.5 to 20.5 % v/v

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