Question

mini lab: the starch test
problem
which foods contain starch? observe the results of adding lugol’s solution to different foods
materials (per group of two)
lugol’s solution dropper 5 test tubes test tube rack
soda cracker potato white bread oatmeal
granulated sugar
procedure

1. place pieces of a soda cracker into a test tube.
2. add 5 drops of lugol’s solution to the test tube. lugol’s solution is a test for starch. if the solution turns dark blue or black, starch is present. record your observations.
3. repeat the procedure using small amounts of peeled potato, white bread, oatmeal, and granulated sugar.

data collection

analyze and conclude

1. of the foods you tested, which contain starch? which do not contain starch?
2. why might this procedure not indicate starch in a dark colored food, such as a graham cracker?

Explanation:

1. Based on standard biological test results for starch with Lugol's solution:

• Foods with starch will react with Lugol's solution to turn dark blue/black. Soda crackers, potato, white bread, and oatmeal are all high in starchy carbohydrates, so they will produce this positive reaction.
• Granulated sugar is a simple sugar (monosaccharide, glucose/fructose) with no starch, so it will not react with the solution.

1. Lugol's solution indicates starch by changing to a dark blue or black color. Dark-colored foods already have a dark natural hue, which masks or makes it impossible to clearly observe the color change that signals the presence of starch.

Answer:

1. Foods containing starch: Soda cracker, potato, white bread, oatmeal

Foods not containing starch: Granulated sugar

1. The dark natural color of the food would mask the dark blue/black color change that indicates starch is present, making the result unobservable.