Practical investigations
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Hello. I have carried out chemistry experiments on white wine, and I have found out that the ethanol content in wine decreased from 13% to 4% in a month. However, for ethanoic acid, it remained close to constant. It increased from 0.4% to 0.5% during the same month [same wine]. I thought that the concentration of ethanoic acid would increase quite significantly because ethanol will oxidise to ethanoic acid [the reason why the ethanol content decreased]. Can you suggest possible reasons for this observation? Why did the ethanoic acid concentration remain constant while that of the ethanol decreased significantly? Almost no evaporation took place during the experiment [during the month].
Igloo writes ...
One or more of the following explanations would account for your observations:
1 The ethanol vaporised away from the wine. Can you be sure that “almost no evaporation took place during the month”?
2 The ethanol may have oxidised to another product, perhaps ethanal, for example.
3 The ethanol may have reacted with one of the many acids present to form esters, this process perhaps being “catalysed” by bacteria whose concentration might be greatly increased by the presence of air.
You are not the first person to have discovered that the ethanol content decreases, whilst the ethanoic acid concentration remains fairly constant once wine has been exposed to air, so I am inclined to believe that your experimental results are sound enough.
Might I suggest that you carry out some “control” experiments? For example, if you made up an aqueous solution in de-ionised water, containing 13% ethanol and 0.4% ethanoic acid, i.e. without all the other components in wine or the bacteria, and leave this for a month under sterile conditions, you would then be able to analyse this and find out what changes in concentration of the ethanol and the ethanoic acid had occurred. The results obtained might help you to come to some useful conclusions.
Always carry out a risk asessment 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: 15 December 2006
