Finding out
A potato is boiled. Does it carry starch, a kind of carbohydrate? Tasting will not tell you.
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Step 1 of 4
- A drop of iodine solution on a boiled potato.
- The drop turns blue-black.
- Blue-black means the food has starch.
- Seeing the colour is an observation. Naming starch is an inference.
The rule
Yes. Iodine turns a boiled potato blue-black. That means the potato carries starch. Iodine solution is a brown liquid.
- Starch test — a drop of iodine. Blue-black means starch, a carbohydrate.
- Fat test — rub the food on paper. An oily mark means fat.
What you see is an observation. What you decide from it is an inference.
This lab is on a screen only. A real test needs the right chemicals and a teacher.
Watch out!
A food with no oily mark can still carry other components. The test checks only for fat.