Lecture
Bring a suspension of a small amount of starch in water to a boil. A starch paste forms. Dilute it with water and carry out the qualitative reaction with iodine. Heat the solution of the blue starch–iodine complex. Discoloration of the solution is observed. For this experiment to succeed, the solution of the iodine–starch complex must be dilute.
Prepare copper(II) hydroxide, add dilute starch paste to it, and heat the test tube. Is dissolution of the copper(II) hydroxide and subsequent reduction of Cu(II) observed?
Drop a solution of iodine onto a piece of white bread and a fresh cut of a potato tuber. What does the appearance of a blue spot at the site of the drop indicate?
Explain the phenomena observed, and write the equations of the reactions taking place.
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