How to identify starch
How to easily identify starch in food
Perform this experiment only under adult supervision.
Reagents and equipment
- copper(II) sulfate;
- potassium iodide;
Mix some copper(II) sulfate and potassium iodide solution in a cup in a 1:2 ratio. Cover a sliced potato and lemon with boiling water and let soak for 5 minutes. Add some drops of the prepared solution to each of the cups. The cup of potato acquires a blue hue. Meanwhile, in the cup with lemon, the solution becomes colorless. If this didn’t happen, then the lemon didn't contain enough vitamin C (ascorbic acid).
Copper(II) sulfate and potassium iodide react to form iodine, which dissolves in residual potassium iodide to yield a brown solution. If this mixture is added to the solution with potato, the contained starch will react with iodine and forms a dark blue starch-iodine complex. If the solution of iodine in potassium iodide is added to the solution with lemon, the iodine reacts with vitamin C (ascorbic acid) and is reduced to colorless iodide ions.
You can find many cool experiments in the MEL Chemistry subscription!