NATURAL SCIENCES
PRACTICAL INVESTIGATION TASK 1
GRADE 9 ………
FEBRUARY 2014
MEMORANDUM
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FOOD TESTING
The nutrients in the food you eat supply your body with energy for growth and repair. These
nutrients include carbohydrates, proteins, fats, minerals and vitamins. The presence of these
nutrients in food can be tested by using chemical indicators /reagents that react in
predictable ways. A colour change of an indicator is usually a positive test for the presence
of a certain nutrient. In this practical, you will use several indicators to test for the presence
of nutrients in solutions.
INSTRUCTIONS:
You will perform FOUR different tests on TWO experimental samples.
Each test will use a different indicator reagent that will change colour in the presence of
the particular organic compound that is being tested for.
As part of the experimental method, you must include control samples to insure the
validity of your results.
A negative control will result in no change in colour. It will either contain no sample at all or
it will contain a nonreactive sample like water.
A positive control will result in a colour change indicating the presence of the compound
you are testing for.
Answer the questions each time the food test has been completed in the
appropriate spaces
Food Test 1: Starch
1. Take small amounts of the unknown food sample or 10 drops of
aqueous solution of the sample in a test tube.
2. Add 3-4 drops of test indicator.
1.1.
Predict which nutrient is present in your unknown food samples above.
Starch√
1.2.
(1)
Give the name of the chemical reagent used in this food test.
Iodine√
(1)
1
1.3.
Name one precautionary measure you applied when you tested for the nutrient
mentioned in 1.1. Give a reason why you applied this measure
Wear a lab coat√ / gloves-iodine stains√
1.4.
(2)
Give the positive results for this food nutrient tested.
If starch is present iodine will change to blue black√√
(2)
Food Test 2: Sugar – Benedict's solution
1. For solid food samples add glucose, fructose to test tubes.
2. If testing more than one liquid, label each test tube with a marker.
3. Add 10 drops of Benedict's solution to each test tube.
4. Carefully heat the test tubes by suspending in a hot water bath for five minutes.
2.1
Predict which nutrient is present in all food samples.
Glucose√
2.2.
(1)
Why do we boil / heat the Benedict solution?
To remove any impurities√√
2.2
(2)
Record your observations in a table. Decide on your own headings for the
different columns.
Test tubes
G1√
G2√
Colour changes
Green√
orange red√
√
(5)
 Headings√
 Numbering of test tubes√√
 Colour changes√√
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Food Test 3: Fat – Spot test using a white paper
1.
2.
3.
4.
5.
3.1
3.2
3.3
Take a food sample to be tested and press or rub it on a clean white sheet of paper.
Hold it against light to see if the paper become translucent or not.
Pour 1 tsp ethanol in each of two test tubes
Add a small amounts of test material into test tube 1 and water into test tube 2.
Shake thoroughly
Predict the main food nutrient present in the food samples.
Fats / lipids√
(1)
Which of the test tubes is the: (a) experiment 1/ ethanol√ and
(b) control 2 /water√
Describe what happens in the experiment.
(2)
After the ethanol was added to food sample and shaken up, a white
emulsion √√formed.
(2)
Food Test 4: Protein – Biuret solution
1. Take small amount of crushed food sample or 10 drops of aqueous solution of the
sample in a test tube.
2. Add 10 drops of copper sulphate to the test material.
3. Add 10 drops of sodium hydroxide. Wait for a couple of minutes
4. Repeat process with all test samples
proteins√
4.1
Predict the organic compound present in the test material
4.2
Name one safety measure that you will apply during this experiment. Give a reason why this
measure will be obeyed.
Treat NaOH & CuSO4 with care√ –they are corrosive substances√ /
wear gloves / lab coat / goggles
(1)
(2)
3
4.3
Describe the results for the positive test
A purple√√ / lilac / violet colour change was seen as soon as the two
chemicals reacted proving that proteins are present in food sample.
(2)
4
5.
CUT OUT AND REARRANGE THESE CARDS TO GIVE YOU DETAILS OF HOW TO TEST FOR
EACH FOOD TYPE. (Paste the correct sequence for each test on a clean A4 page.)
(6)
 4 X 1 FOR CORRECT SEQUENCE OF STEPS
 2 X 1 FOR NEAT WORK
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