Does temperature have an effect on pH of orange juice?


Introduction/Hypothesis

If the temperature is low, then the pH will be high because the movement of the orange juice particles will be slowed down.

Annotated bibliography for background information

From this source, we learned that pH typically changes with temperature. However, the correlation depends on the make-up of the substance. This helped us formulate our hypothesis. The source is reliable because it written by a college professor.
From this source, we learned that pH goes down as temperature rises. This was a key factor in developing our hypothesis. It is reliable because it is from a test that a class at the Australian and New Zealand College of Perfusionists ran on blood.
From this source, we learned that there is a need for temperature compensation in pH meters. This means that temperature does have an effect on pH. The article said that pH measurements can be faulty due to unexpected temperature changes. This is a reliable source because it is written by a company that makes pH test meters.
From this source we learned that temperature has multiple effects on pH. This is a reliable source because it is report from a company that sells laboratory equipment.

Materials List

    • 4 containers
    • 5 cups of orange juice
    • pH test strips
    • 33 degree refrigerator
    • -2 degree freezer
    • Microwave
    • Cooktop
    • Small pot
Procedure
1. Obtain five cups of orange juice.
2. Use pH strips to test pH level of orange juice and record in chart.
3. Pour each cup in a different container.
4. Take pH of orange juice that has been in a refrigerator and record in chart.
5. Place one container in a room temperature area and leave for one day.
6. Place one container in a -2 degree freezer and leave for one day.
7. Microwave one container on medium.
8. After taking container out of microwave, use pH test strips to test pH and record measurement in chart.
9. Boil one cup of orange juice on high for 5 minutes. When finished boiling, use pH strip to test pH. Record measurement in chart.
10. Remove container from freezer, test it’s pH and record in chart.
11. Remove container from room temperature area, test it’s pH and record in chart.
Variables and Controls
Independent: Temperature
Dependent: pH of orange juice
Control: Juice in fridge

Data Recordings

Temperature
pH
-2°F
5
33°F
5
76°F
5
173°F
5
212°F
5

Charts and Graphs


Conclusions

From this project, we learned that temperature has no effect on pH. We tested the orange juice that was in the refrigerator and used that as a constant. Our original thoughts were that it’s pH would be about a 6. We thought that the colder orange juice would have a pH level greater than that and the warmer orange juice would have a lower pH. When we got 5 as the pH of the 33° orange juice, we were surprised. This made thought of any realistically higher or lower pH levels unlikely. As the experiment went on, we continued to get 5 as the pH of all of the juices. These results contradicted our hypothesis.

Sources of Error

A possible source of error is reading the pH incorrectly. The 5.5 and 5.0 pH levels look very similar on the test strips.