Biology 2.1.2 Chemical Tests Flashcards
What does the Biuret test detect?
The Biuret test detects proteins by indicating the presence of peptide bonds, specifically in polypeptides and proteins.
How is the Biuret test performed?
Add an equal volume of Biuret reagent (which contains copper(II) sulfate) to the sample. Mix gently and observe for color change. A positive result shows a color change to purple, while a negative result remains blue.
What does a positive result in the Biuret test indicate?
A purple color indicates the presence of proteins, whereas no color change (remains blue) indicates the absence of proteins.
What does Benedict’s test detect?
Benedict’s test detects reducing sugars (e.g., glucose, fructose) and, after hydrolysis, can also detect non-reducing sugars (e.g., sucrose).
How is the Benedict’s test performed?
Mix the sample with an equal volume of Benedict’s reagent. Heat the mixture in a boiling water bath (around 95°C) for 2-5 minutes. Observe for color change.
What are the color changes in the Benedict’s test?
Blue: No reducing sugar (negative)
Green: Low concentration
Yellow: Moderate concentration
Orange: High concentration
Brick red: Very high concentration
How is the test for non-reducing sugars conducted?
Boil the sample with dilute hydrochloric acid for 5 minutes to hydrolyze. Neutralize with sodium hydroxide, then perform the Benedict’s test as described.
What do reagent test strips detect?
Reagent test strips detect reducing sugars quickly. They change color based on the concentration of sugar present in the solution. The darker the colour, the higher the concentration of the sugar present in solution.
How are reagent test strips used?
Dip the strip into the solution and compare the color change to a standard chart to determine the concentration of reducing sugars.
What does the iodine test detect?
The iodine test detects starch, forming a blue-black colour from orange-brown colour.
How is the iodine test performed?
Add a few drops of iodine solution to the sample on a white tile or in a test tube. A blue-black color indicates the presence of starch, while a brown color indicates its absence.
What does a positive emulsion test indicate?
A positive emulsion test indicates the presence of lipids, shown by a milky emulsion.
How is the emulsion test performed?
Dissolve the sample in an equal volume of ethanol and shake. Then add water and mix gently. A milky emulsion forms if lipids are present, while a clear solution indicates their absence.
