Lean Construction

an adult sensitive balance 0.25 gram of indophenol (2,6- dichloroindophenol, sodium salt) water

measuring cup or graduated cylinder

2 pairs of rubber or plastic gloves

2 pairs of safety glasses

clean 2-liter plastic soda bottle 500 milligram (0.5g) of vitamin C paper hammer cup measuring teaspoon

clear plastic vials or medicine cups

eyedropper toothpicks

notebook and pencil sink

lemon juice from concentrate pulp-free orange juice

orange juice prepared from frozen concentrate

canned orange juice grapefruit juice Kool-Aid Tang

apple juice

various reasonably clear juices that are not red or purple

clear soda

You can test substances to see if they contain vitamin C (ascorbic acid) by using a chemical called indophenol. Its

more technical name is sodium 2,6- dichloroindophenol, in case you have to buy some from a chemical supply

company.

A freshly prepared solution of

indophenol has a bluish color, but it turns colorless as vitamin C is added to it. You can compare the concentrations of vitamin C in different liquids by adding the liquids drop by drop to a fixed amount of indophenol solution. For example, suppose it takes only 2 drops of liquid X to turn 10 ml of an

indophenol solution colorless. If it takes 6 drops of liquid Y to turn an identical sample of indophenol colorless, liquid Y

contains about one third as much vitamin C as liquid X.

Ask an adult to help you prepare a

solution of indophenol just before your experiment because indophenol

deteriorates with time. Indophenol

powder should not touch your skin or eyes. Therefore, you should both wear gloves and safety glasses while

preparing the solution. The solution

will be very dilute and far less harmful than the powder, so if any of the solution touches your skin simply rinse it off with water.

To prepare the indophenol solution that you will use, have an adult add 0.25 g

of indophenol to 2.0 liters (2,000 ml) of water. (A clean 2-liter plastic soda bottle can hold all of the solution.) Stir or seal and shake to dissolve the solid. What is the percentage of indophenol in this solution? (Remember: 1.0 ml of water weighs 1.0 g.)

Next, crush 500 mg (0.5 g) of vitamin C. One 500-mg or two 250-mg vitamin C tablets will provide all the vitamin C you need. Place the tablet(s) on a piece of paper and strike the solid gently with a hammer. Press the particles with the hammer until you have a powder. Add the vitamin C powder to 100 ml of water in a cup. Stir until all the solid has

vitamin C in this solution? You will use this solution as a standard vitamin C concentration. Other liquids that you test will be compared to this concentration of vitamin C.

Measure out 10 ml (2 tsp) of the indophenol solution and pour it into a clear plastic vial or a medicine cup. Pour 10 ml (2 tsp) of water into an identical vial or medicine cup. The water will serve as a control.

Comparing the indophenol solution with the water will help you decide when the indophenol has become colorless.

Place the two vials or medicine cups side by side. Using an eyedropper, add 1

drop of the vitamin C solution to the indophenol. Then add 1 drop of the vitamin C solution to the vial or test tube that contains water. Use separate

toothpicks to stir each solution. Has the vitamin C changed the color of the indophenol solution? Does the

indophenol solution now match the color of the liquid in the vial of water? If not, continue to add the vitamin C solution 1 drop at a time to the indophenol and to the water. Do this until the bluish

indophenol solution becomes colorless (not violet or pink, which may appear as an intermediate step) and has the same appearance as the vial or tube that

of drops required to turn the indophenol colorless in your science notebook. Rinse the vials or test tubes and the eyedropper thoroughly with water in a sink. Then repeat the test, but this time use the liquid obtained from a freshly squeezed lemon. How many drops of fresh lemon juice are required to turn the indophenol from blue to colorless?

Record your results. How does the vitamin C content of the lemon juice compare with that of the vitamin C solution?

Repeat the test again using drops of lemon juice from concentrate. Record your results. How does the vitamin C

content of the lemon juice from concentrate compare with that of the vitamin C solution? With that of the fresh lemon juice?

Use this experiment to test a number of other liquids for vitamin C. You might try pulp-free orange juice, orange juice prepared from a frozen concentrate, canned orange juice, grapefruit juice, Kool-Aid, Tang, apple juice, other juices that are reasonably clear, and a clear soda such as 7UP or Sprite. Which ones do you think will be good sources of vitamin C? After performing the tests, which ones do you conclude are good sources of vitamin C? Which are poor sources of vitamin C?

Make a list of the liquids you have tested in order of their vitamin C content

Science Fair Project Ideas

Design and conduct an experiment to find out how leaving a vitamin C-rich liquid exposed to the air affects its concentration of vitamin C. Design and conduct another experiment to see how lack of refrigeration affects the vitamin C concentration of a vitamin C-rich liquid.

Investigate how you might test for the presence of other vitamins.

Chapter 3

Yeast, Baking Soda,