Name _______________________________
Foaming Spuds
Period ______ Date ___________ Seat _____
Adapted from a 2012 Biology COE Update
Directions: Use the following information to answer questions 3-10 on pages 3 – 6.
Mike and Kelsey were studying how hydrogen peroxide (H2O2) in cells breaks down to form water and
oxygen. When this reaction happens, bubbles of oxygen gas are released,
2H2O2
hydrogen peroxide
→
→
2H2O
water
+
O2
oxygen
A protein named catalase, found in all cells including potatoes, increases the rate of this reaction. Mike and
Kelsey used potato juice as the source of catalase to do the following controlled experiment.
Question: What is the effect of the pH of potato juice on the height of foam produced when hydrogen
peroxide is added to potato juice?
Mike’s and Kelsey’s Prediction: As the pH of potato juice decreases (higher acidity), the height of foam will
increase.
Materials:
Four large test tubes (16mm x 150mm) labeled pH4, pH 6, pH 8 and pH 10.
Four small test tubes (16mm x 100mm)
Potato juice from the same potato, divided and adjusted to four pH values: pH 4, pH 6, pH 8, and pH 10
Hydrogen peroxide (3% H2O2)
Stopwatch
Stirring rod
Thermometer
Test tube rack
25mL graduated cylinder (to measure potato juice)
10mL graduated cylinder (to measure hydrogen peroxide)
Metric ruler
1
Name _______________________________
Foaming Spuds
Period ______ Date ___________ Seat _____
Adapted from a 2012 Biology COE Update
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Label four large test tubes, one for each pH value.
Put 6 milliliters of potato juice at pH 6 in the appropriately labeled large test tube.
Do the same for each of the other large test tubes.
Monitor the room temperature to make sure the temperature remains the same throughout the
investigation.
Add 3 milliliters of hydrogen peroxide to each small test tube.
Working left to right, pour the hydrogen peroxide from the small test tubes into each large test
tube.
Working left to right, use a stirring rod to mix the contents in each test tube. Use a paper towel to
wipe clean the stirring rod between mixings. Wait 1 minute.
Working left to right, use a wax pencil to mark the upper and lower limits of foam in each test tube.
Measure and record the height of foam in each test tube as Trial 1.
Clean all test tubes and stirring rod.
Repeat steps 1 through 10 two times for Trials 2 and 3.
Calculate and record the average height of foam for each pH value of potato juice.
Data:
pH of Potato Juice vs. Height of Foam
pH of
Potato
juice
3
5
7
10
Trial 1
Height of Foam (millimeters)
Trial 2
Trial 3
Average of
three trials
From computer
spreadsheet
All- class
average
1. How could Mike and Kelsey be more certain the results of their experiment are reliable?
a. Test the reaction with other acidities of potato juice.
b. Repeat the experiment in the same way.
c. Increase the volume of potato juice.
d. Use a different type of plant juice.
2. What did Mike and Kelsey do to make the results of their experiment valid?
a. Recorded the height of the foam in centimeters.
b. Calculated the average height of foam for each pH.
c. Measured the height of foam at each pH three times.
d. Waited three minutes before measuring the height of foam.
2
Name _______________________________
Foaming Spuds
Period ______ Date ___________ Seat _____
Adapted from a 2012 Biology COE Update
3. Write a conclusion for this controlled experiment.
In your conclusion, be sure to:
 Answer the experimental question.
 Include supporting data from the pH of Potato Juice vs. Height of Foam table.
 Explain how these data support your conclusion.
 Provide a scientific explanation for the trend in the data.
Question: What is the effect of the pH of potato juice on the height of foam produced when
Hydrogen peroxide is added to potato juice?
Conclusion:
3
Name _______________________________
Foaming Spuds
Period ______ Date ___________ Seat _____
Adapted from a 2012 Biology COE Update
4. Plan a controlled experiment to answer the question in the box. You may use any materials and
equipment in your procedure.
Be sure your procedure includes:



Logical steps to do the experiment
Two controlled (kept the same) variables
One manipulated (independent) variable
• one responding (dependent) variable
• how often measurements should be taken
and recorded
Question: What is the effect of the temperature of potato juice on the time for bubbling to stop
After hydrogen peroxide is added?
Procedure:
4
Name _______________________________
Foaming Spuds
Period ______ Date ___________ Seat _____
Adapted from a 2012 Biology COE Update
Self-Scoring Rubric (Conclusion)
Attributes
Conclusive statement:
Supporting data for pH 6:
Supporting data for pH 9:
Explanatory language:
Scientific explanation:
Total Attributes & Score Points
Attribute Name
Self-Scoring Rubric (Experiment Design)
Credit
Description / Evidence of Attribute
Controlled Variables
Manipulated Variable
Responding Variable
Record Measurements
Trials are Repeated
Extra Validity Measure
Logical Steps
Total Attributes
Score Points
5