Nuffield Advanced Chemistry - Hi, I'm doing an investigation into the acids in wine for my coursework, and I'm planning on performing tlc on the wines to determine the carboxylic acids that are present. I've read that I should use butan-1-ol, methanoic acid and water in a 8:1:2.5 ratio, but I can't find the concentrations I should use, do you have any idea? Also, I have read that I should use bromocresol green as the indicator, but my school only has the solid. I found a recipe for the indicator to be 0.3% in a 1:4 water-methanol mixture, but again, there was no mention of the methanol concentration, and I'm not really sure if this is the recipe I should use. Do you know whether this would be appropriate, or could you advise me on another method?

Practical investigations

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Hi,
I'm doing an investigation into the acids in wine for my coursework, and I'm planning on performing tlc on the wines to determine the carboxylic acids that are present. I've read that I should use butan-1-ol, methanoic acid and water in a 8:1:2.5 ratio, but I can't find the concentrations I should use, do you have any idea?
Also, I have read that I should use bromocresol green as the indicator, but my school only has the solid. I found a recipe for the indicator to be 0.3% in a 1:4 water-methanol mixture, but again, there was no mention of the methanol concentration, and I'm not really sure if this is the recipe I should use. Do you know whether this would be appropriate, or could you advise me on another method?

Corrie writes ....

The substances your are using to make up your solutions (butan-1-ol, water, methanoic acid etc) are all pure substances, not solutions. Therefore talking about their concentrations is not applicable here.

When it says a 8:1:2.5 mixture it means 8 parts of butan-1-ol, 1 part methanoic acid and 2.5 parts water. As these are all liquids, it will be parts by volume, for example 8 cm³ butan-1-ol, 1 cm³ methanoic acid and 2.5 cm³ water - or any multiple of this ratio.

The same applies to the 1:4 water-methanol mixture - for example, just mix 10 cm³ water with 40 cm³ methanol if you want 50 cm³ of indicator solution.

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: 02 April 2007

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