What is the iodine test for potato juice?

1. Take 10 mL of fresh potato juice in a clean test tube.

2. Add a few drops of dilute (0.1%) iodine solution to the test tube.

3. Observe the colour change.

Expected Result:

The potato juice will turn bluish black.

Explanation:

This is a positive test for the presence of starch. Iodine reacts with the starch molecules in the potato juice to form a complex called starch-iodine complex. This complex is bluish black in colour.