Experiment WS 5: 7.4A & B

Kowloon Tong School (Secondary Section)

F.2 Integrated Science

Experiment Worksheets 5

Name: _________________ (    )                                                               Date: __________________

Class: 2 _______

Experiment 7.4A: The iodine test碘液試驗 for starch澱粉

Objective:       To test for starch using iodine solution碘液

Results:

Liquid	Colour after adding iodine solution
Starch solution	Dark blue
water	Brown

Conclusion:

Ø   Iodine solution can be used to test for starch.

Ø   A colour change from brown to blue shows the presence of starch.

Experiment 7.4B: Tests for starch in green leaves

Objective:       To test for starch in green leaves using iodine solution

3.  (a) Take the leaf out of the alcohol. Observe what happens to the colours of the leaf and the alcohol.       The leaf becomes pale green and the       alcohol becomes green in colour.
(b) Put the leaf in the beaker of hot water for half a minute. Observe what happens to the leaf.       The leaf becomes soft.
4.  Carefully spread the leaf on a white tile. Add a few drops of iodine solution to it. Observe what happens.    This leaf is now dark blue in colour. This shows that    starch is present in the leaf.

Discussion:

What is the purpose目的 of each step above? Write the letters representing the purposes on the blanks below.

Step		Purpose
1.   Put the leaf in boiling water.	c	(a) To test for the presence of starch in the leaf.
2.   Put the leaf in hot alcohol.	d	(b) To wash away the alcohol and to soften軟化 the leaf.
3.   Put the leaf in hot water again.	b	(c) To kill the leaf cells so that iodine solution can enter the cells later on.
4.   Add iodine solution to the leaf.	a	(d) To remove清除 the chlorophyll葉綠素 to make the leaf lighter in colour for easy observation of the results of the iodine test.