Practical investigations
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Hi, I'm doing the investigation about acidity content of vinegars. I carried out a successful titration but am having difficulty with the chromatography. I tried using water as a solvent, but all the acids I used (tartaric, malic, succinic, ethanoic and lactic) rose to the same point. I have just tried butanol as a solvent and the results are clearer but very close together, and the vinegars themselves don't seem to do a lot! The indicator I'm using is bromophenol blue. Any ideas where I might be going wrong or what I can do? Thanks.
Igloo writes ...
Getting good results is very much a matter of trial and error. There is nothing you are doing wrongly, but you might try one or more of the following alternative procedures:
Try using a mixture of butan-1-ol and water.
Try using bromocresol green instead of bromophenol blue.
Try using a different support medium, e.g. silica plates instead of chromatography paper.
Try using smaller spots, so that that the results are better defined and give measurable Rf values.
In my experience, different vinegars tend to produce similar results. This is because they probably contain the same mixture of acids, but in different proportions. Unfortunately the chromatography you are carrying out is not designed to give quantitative information.
Do remember to include all your experiences in your report. You should be given credit for persevering and trying out different methods where earlier ones have failed. This is what research is all about!
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.
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updated: 05 April 2006
