Practical investigations
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I am doing my coursework on vinegars and I am trying to find out whether vinegars meet the law specification of 4% (w/v) ethanoic acid. I know vinegar contains other acids apart from ethanoic, so I have to separate ethanoic from the vinegar. I can’t find how to separate it. When I do separate it, do I dilute the separated ethanoic acid before titrating it? Please help, I’m soo confused!
Igloo writes ...
As you realize, there are plenty of other acids in the vinegars apart from ethanoic acid. Fortunately most of these “other acids” are non-volatile, i.e. do not distil over when the vinegar is distilled. All you have to do then is to distil a sample of your vinegar, designing your apparatus in such a way that as little ethanoic acid vapour is lost to the surroundings as possible. Once all the acids have distilled over (how will you know this?) you can make up the distillate to a known volume in a volumetric flask, and carry out titrations on portions of this solution, using a standard solution of alkali and phenolphthalein as indicator. We introduce these ideas in a tutorial on this website.
Of course in your calculations you have to assume that ethanoic acid is the chief component of your distillate, but, apart from small amounts of other acids, maybe propanoic acid, this is a reasonable assumption to make.
Don’t forget to carry out a risk assessment before carrying out your practical work and also to gain permission from your teacher.
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: 25 February 2005
