Sahil placed some pieces of chapati in test tube A. Neha placed chewed chapati in test tube B, and Santushti took boiled and mashed potato in test tube C. All of them added a few drops of iodine solution to their test tubes—A, B, and C, respectively. What would be their observations? Give reasons.
Test tube A (pieces of chapati): The iodine solution will turn blue-black because starch is present in the chapati pieces.
Test tube B (chewed chapati): The iodine solution will show no colour change or a very light blue-black colour because the saliva in the chewed chapati has broken down starch into simple sugars.
Test tube C (boiled and mashed potato): The iodine solution will turn blue-black because potato contains starch which has not been broken down.
Iodine gives a blue-black colour when it reacts with starch, indicating the presence of starch.
Explanation
The chapter describes Activity 9.1 which demonstrates that iodine gives a blue-black colour when it reacts with starch. In test tube A, the chapati pieces contain starch, so the iodine will turn blue-black. In test tube B, the chewed chapati has been acted upon by saliva, which contains digestive juices that break down starch into sugars, so there will be little or no colour change. In test tube C, boiled and mashed potato contains starch but no saliva has acted on it, so the iodine will turn blue-black.
Solution Steps
Iodine solution turns blue-black when it reacts with starch, indicating starch presence.
Test tube A (chapati pieces) contains starch, so iodine turns blue-black.
Test tube B (chewed chapati) has saliva that breaks down starch into simple sugars, so little or no colour change occurs.
Test tube C (boiled and mashed potato) contains starch with no saliva action, so iodine turns blue-black.