Part 4: Chemical Food Tests

Question 1

Describe the food test for starch.

Answer 1

Name of reagent: iodine solution
Details of test: Add a few drops of iodine solution
Colour if present: blue- black
Colour if absent: yellow

Question 2

Describe the food test for glucose

Answer 2

Name of reagent: Benedict’s reagent
Details of test: Add Benedict’s and heat
Colour if present: brick red, orange, yellow, green
Colour if absent: blue

Question 3

Describe two food tests for lipids

Answer 3

Test 1
Name of reagent: ethanol
Details of test: add ethanol to food and shake, then pour slowly into water
Colour if present: cloudy emulsion
Colour if absent: no emulsion
Test 2
Name of reagent: Sudan III
Details of test: add water, then add Sudan III and shake- wait a few minutes
Colour if present: red layer on top
Colour if absent: no red layer on top

Question 4

Describe the food test for proteins

Answer 4

Name of reagent: Biuret reagent
Details of test: add Biuret and wait a few minutes
Colour if present: purple
Colour if absent: pale blue

Question 5

Explain what is meant by a positive control experiment

Answer 5

A positive control experiment is an experiment that uses a treatment that is known to produce results (e.g. testing pure starch with iodine solution). This allows comparison with your results.

Question 6

Explain what is meant by a negative control experiment.

Answer 6

A negative control experiment is an experiment that will not produce results (e.g. testing water with iodine). This enables comparison and shows whether the test has worked properly.

Question 7

Suggest why scientists carry out positive control experiments.

Answer 7

Shows an expected result to help scientists understand that the experiment was performed properly.

Question 8

Suggest why scientists carry out negative control experiments.

Answer 8

To see if there are any unknown variables that are in the experiment.