Testing for biological
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Describe the Benedict's test and its positive result.
The Benedict's test identifies reducing sugars. Add Benedict's reagent to a sample and heat in a water bath. A positive result is a color change from blue to green/yellow/orange/red, indicating the presence of reducing sugars.
What is the purpose of the iodine test?
The iodine test detects the presence of starch. Iodine solution (potassium iodide) is added to the sample. A positive result is a color change from yellow/brown to blue/black, indicating starch presence.
Outline the emulsion test for lipids.
The emulsion test identifies lipids. Mix the sample with ethanol, then add water. A positive result is a milky white emulsion forming, indicating the presence of lipids.
Describe the Biuret test and its positive result.
The Biuret test detects proteins. Add Biuret reagent (copper(II) sulfate and sodium hydroxide) to the sample. A positive result is a color change from blue to purple/violet, indicating protein presence.
How can a semi-quantitative Benedict's test be carried out?
A semi-quantitative Benedict's test involves standardising the procedure (
Explain the purpose of acid hydrolysis when testing for non-reducing sugars.
Acid hydrolysis breaks down non-reducing sugars into their constituent reducing sugars. This allows them to be detected by the Benedict's test, which cannot directly react with non-reducing sugars like sucrose.
Outline the procedure for testing for non-reducing sugars after acid hydrolysis.
Boil the sample with hydrochloric acid, then neutralise with sodium hydrogencarbonate. Perform the Benedict's test. A positive result (color change) indicates the presence of non-reducing sugars in the original sample.
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