Question

As part of a science experiment, Jose did a test for starch on a slice of apple and a slice of potato. The yellow-orange iodine solution stayed the same color when it was put on the apple, but it became black on the potato. Why did the iodine solution change color on the potato?

Answer 1

If iodine solution reacts with starch, it will change color into black.
Since the yellow-orange iodine solution stayed the same color when it was put on the apple, it can be concluded that there is no starch in the apple. On the other case, the black color of the potato suggests that there is a great amount of starch in the potato. Anyway, this does not mean that there is no starch in the apple at all. As fruits ripen, starch slowly changes to sugar. Iodine cannot react with sugar, so the black color in the apple is missing.