Year 9 Term 1 - Food Tests [print-friendly version]

Term 1 - Experimental Assessment

Due date:  to be announced separately by teachers in various classes, since experiments will be performed at different times.

Marks: 5 marks for practical procedure in class + 10 marks for formal report. (See your booklet for marking criteria)

Testing For Carbohydrates

Aim: 

Part A:  to determine suitable tests for monosaccharides, disaccharides and polysaccharides.

Part B:  To use the tests from Part A to identify the various carbohydrates in food.

Materials:

Procedure:

Copy your result tables into your practical notebook.

Part A:

1.            Set up a hot water bath by boiling approximately 100-150 mL of water in your beaker.

2.           Put about 1 cm of glucose, sucrose and starch solutions into three separate clean test tubes.  Add about 1 cm of Benedict’s solution to each test tube.

3.           Heat the tube by placing in the water bath for 1-2 minutes.  Record any colour changes in table 1.

4.           Place a small sample (about 10-15 drops) of glucose, sucrose and starch solutions onto three separate clean watch glasses. Add four drops of Iodine solution to each watch glass. Record any colour changes in table 1.

Part B:

1.            Put a small sample of each food into six separate clean test tubes.  Add about 1 cm of Benedict’s solution to each test tube.

2.           Heat the tube by placing in the water bath for 1-2 minutes. 

3.           Record any colour changes in table 2.

4.           Place a small sample of each food onto six separate clean watch glasses. Add four drops of Iodine solution to each watch glass. Record any colour changes in table 2.

Results:

Part A - Table 1

Part B - Table 2

Questions:

1. How can you tell by using Benedict’s and Iodine solution if a carbohydrate is a

        (a) glucose?

        (b) sucrose?

        (c) starch?

2. Give an example of a food that is

        (a) a monosaccharide.

        (b) a disaccharide.

        (c) a polysaccharide.

3. Give an example of a food that contains a large amount of a

        (a) a monosaccharide.

        (b) a disaccharide.

        (c) a polysaccharide.

5. If a food shows no colour change when tested with Benedict’s solution, what type of saccharide is it?

6. What result did you observe for foods tested with Benedict’s solution when only a small amount of glucose was present.

7. Explain how you would test a sample of a new brand of cereal to check the manufacturer’s claim that it contained glucose and starch.

Reference:  Chapman, B., Perry, L., Russell, D., Stead, K., Science 9.

Refer to your Food & Digestion Booklet or Practical report format for the method to write up your formal report.