Alcohols
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I am doing the finding the percentage of ethanol in wine practical and am going to use the titration method. Some sites have said to reflux the ethanol with acidified potassium dichromate whilst others have said to heat the solution in a water bath for 30 mins at 60 °C. Which method is best to use? Do I need to do both, and then do I let it cool before titrating or do I have to titrate with it warm?
Igloo writes ...
Both methods are appropriate. The advantage of the reflux method is that you can ensure the complete oxidation of the ethanol in a relatively short time, but it is more fiddly to set up the apparatus. It is also vital to ensure afterwards that all the mixture is carefully and completely transferred from the reflux apparatus so that none of the excess potassium dichromate is lost.
The second method probably ensures that virtually all the redox reactions have occurred in the 30 minutes in the waterbath, and, in addition, there are fewer problems associated with the transfer of mixture. In addition the second method is safer, in that potassium dichromate is a rather hazardous material, and refluxing involves temperatures in excess of 100 °C.
In summary I would use method 2, but please ensure that you have carried out all the necessary risk assessments beforehand and do take appropriate care when handling the chemicals.
There is no need to use both methods. Allow the mixture to cool before carrying out the titration(s).
Always carry out a risk assessment and check with your teacher before starting any practical work.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 28 November 2007
