Comparing Vitamin C in Fruit Juices
Various brands of juices claim to be good sources of vitamin C, but which juices are the best sources? Vitamin C is an organic acid called ascorbic acid. Like other acids, vitamin C reacts with indicators to produce a color change. This reaction can be used to determine the amount of vitamin C present in foods, such as fruit juices. In this lab, you will add an indicator to a sample of apple juice. The indicator will change color when all the vitamin C has reacted. Then you will test and compare the vitamin C content in other juices with the results for apple juice.
Problem Which juice provides the most vitamin C?
Materials
apple juice
a variety of other fruit juices
test tubes and rack
10-mL graduated cylinder
methylene blue indicator in dropper bottle
stirring rods
Skills Observing, Measuring, Analyzing Data
Procedure
Part A: Measuring Vitamin C in Apple Juice
On a sheet of paper, copy the data table.
Use a graduated cylinder to measure 10 mL of apple juice. Pour the juice into a test tube.
Type of Juice |
Number of Drops |
---|---|
Apple |
|
|
|
|
|
|
|
|
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Add a drop of methylene blue indicator to the test tube. Stir until the color of the indicator disappears.
Add more indicator, one drop at a time, stirring after each addition. Count the drops you add. Stop adding the indicator when the last drop of indicator does not change color. Record the number of drops you used.
Part B: Measuring Vitamin C in Other Juices
Formulate and record a hypothesis about which juice will have the greatest amount of vitamin C. You will need to decide which variables must be kept the same, as well as how to account for bits of solid in some juices.
List the steps in your procedure and write the names of each of the juices to be tested in the left column of your data table.
Have your teacher check your procedure before you begin your experiment.
Analyze and Conclude
Using Graphs Make a bar graph of your data. Which juice required the most drops of indicator? Which required the least?
Drawing Conclusions Based on your data, which juice contained the most vitamin C? How did you reach this conclusion?
Evaluating and Revising What unexpected problems did you encounter? Explain how you could revise your procedure to avoid these problems.