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Food Tests Quiz

The document provides instructions for students to carry out qualitative food tests to identify carbohydrates, lipids, and proteins in different foods using Benedict's test for sugars, iodine test for starch, emulsion test for lipids, and Biuret reagent for proteins. It describes how to prepare food samples and cautions students to take safety precautions when using chemicals and heat sources. Students are asked to analyze results from food tests on samples A, B, and C to determine which molecules are present or absent in each food.

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Oyasor Ikhapo Anthony
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237 views7 pages

Food Tests Quiz

The document provides instructions for students to carry out qualitative food tests to identify carbohydrates, lipids, and proteins in different foods using Benedict's test for sugars, iodine test for starch, emulsion test for lipids, and Biuret reagent for proteins. It describes how to prepare food samples and cautions students to take safety precautions when using chemicals and heat sources. Students are asked to analyze results from food tests on samples A, B, and C to determine which molecules are present or absent in each food.

Uploaded by

Oyasor Ikhapo Anthony
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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3RD OCTOBER, 2021

SUNDAY

BIOLOGY
PRACTICAL BIOLOGY
REVISION EXERCISE
Required Practical: Food Tests
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Food Tests
• Aim: To use qualitative reagents to test for a range of carbohydrates, lipids and proteins. To
include: Benedict’s test for sugars, Iodine test for starch, the emulsion test for lipids and the
Biuret reagent for protein
• You will:
o Use qualitative reagents to test for the presence of key biological molecules in a
range of foods
o Safely use appropriate heating devices and techniques including the use of a Bunsen
burden and a water bath
• A qualitative food test indicates if a substance is present or absent in a sample (although it
doesn’t tell you how much is present)
• Observations are essential in this practical; you are looking for colour changes in particular
which can indicate if a substance is present or absent:

Food test colour changes table


Preparing a sample
• Before you can carry out any of the food tests described below, you may need to prepare a
food sample first (especially for solid foods to be tested)
• To do this:
o Break up the food using a pestle and mortar
o Transfer to a test tube and add distilled water
o Mix the food with the water by stirring with a glass rod
o Filter the mixture using a funnel and filter paper, collecting the solution
o Proceed with the food tests
It is important that you carry out the tests methodically, recording your observations carefully

Important hazards
• Whilst carrying out this practical you should try to identify the main hazards and be thinking
of ways to reduce harm:
o Biuret solution contains copper (II) sulfate which is dangerous particularly if it gets in
the eyes, so always wear goggles
o Iodine is also an irritant to eyes (wear goggles)
o Sodium hydroxide in biuret solution is corrosive, if any chemicals get onto your skin
wash hands immediately
o Ethanol is highly flammable; keep it away from the Bunsen burner used in the
Benedict’s test (you should turn the Bunsen off completely)
o And of course, the Bunsen itself is a hazard!
Be prepared to explain what molecules are or are not present in a food sample – make sure you
know the positive and negative results for each test

A student is carrying out food tests.

Her results are shown below.

Observations with Observations with the Observations with the


Food
iodine solution biuret test Sudan III test
A red layer floating on
A Blue-black coloration Purple coloration
the surface
No separate layer
B Brown coloration Blue coloration
produced
The food was coloured
No separate layer
C Blue-black coloration so no colour change
produced
could be observed
What conclusions can be drawn about the three foods, A, B and C?

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