Hannah Eckert, Lake Rouse, Kathleen Bradey, Marecole Carr
Mrs. Bostic
APES 3rd
30 August, 2014
Ocean Acidification Lab
Introduction:
From 1751 to 1994, the pH of ocean water has decreased from 8.2-8.1 but there still has been an
increase in acidity. Since the industrial revolution began, we have released 2 trillion tons of
carbon dioxide into the atmosphere, and about one-third of it went into the ocean. There has been
a 30% increase in acidity of the ocean since 1700. Plants and animals in the ocean have evolved
to thrive on a neutral pH, with the pH becoming more and more acidic, the marine life is
immediately affected. Every day, the ocean absorbs more than 100 million metric tons of carbon
each hour. Ocean acidification is causing decrease in the amount of fisheries, their production,
and ocean life habitats.
Problem: How does carbon dioxide affect the pH of water?
Hypothesis:
If CO2 is added to ocean water and distilled water, then distilled water will change the most in
pH because it is starting out with the least amount of carbon already in it.
Parts of the Experiment:
Control Group: The distilled water
Experimental Group: The ocean water
Independent Variable: Difference in pH
Dependent Variable: Final pH
Controlled Variables: 10mL of water/universal indicator, the person exhaling CO2
Materials:
2 test tubes, universal indicator, ocean water, distilled water, straw, plastic pipet, calcium
carbonate
Procedure:
1. Use a graduated cylinder to measure 10 ML of ocean water. Pour it into test tube
#1. Add 10 mL of universal indicator. Stir and record pH in the table below.
2. Use a graduated cylinder to measure 10 ML of distilled water. Pour it into test
tube #1. Add 10 mL of universal indicator. Stir and record pH in the table below.
3. Blow up a large balloon and secure the opening with a twist tie (Hint: twist the
balloon neck before securing opening).
4. Cut the end off of the bulb of a plastic pipet. Insert into the balloon neck.
5. Place the tip of the pipet in the ocean water sample. Undo the twist tie and slowly
release pressure on the balloon’s neck.
6. Use a stopwatch to start timing as soon as the pressure is released and the solution
begins bubbling. Stop timing as soon as the color changes. Record your data
below.
7. Repeat the procedure using the sample distilled water. Record your data below.
8. Add crushed calcium carbonate to the ocean water and distilled water test tubes.
Record your results.
Data Table
Solution Measured pH Measured pH
after adding CO2
Time (in seconds)
for pH to change
Observations
with calcium
carbonate
Ocean Water 7 About 5.5 10 Seconds Turned a light blue, changed really quickly
Distilled water 7 6 10 Seconds Cloudy Yellow, did not change as quickly as the ocean water
Ocean Water Universal Indicator
After added CO2
After added Calcium
Carbonate
Conclusions
1. What is the most common pH of surface ocean water?
The most common pH of surface ocean water is 8.2-8.1
2. How does your pH of ocean water compare to that reported in the background
information? If there is a difference, provide possible explanations.
The pH of our ocean water is more acidic. A reason for this could because our ocean was
a small amount, and there is a possibility of other contaminants that were already in the
Distilled Water
Universal Indicator
After added CO2
After added Calcium
Carbonate
water. Also there are different oceans in the world so depending on what ocean the water
comes from will be the deciding factor of the pH.
3. Did the distilled water and ocean water respond differently to the added CO2?
Explain your results.
Yes, the ocean water became more acidic than the distilled water when CO2 was added.
A reason for these results could be sea water is more resistant to changes than fresh
water. Sea water has an excessive amount of hydrogen ions released into ocean waters,
causing the ocean to become more acidic.
4. Explain what happened when the calcium carbonate was added to the water
samples.
The ocean water recovered quickly, becoming more basic. The distilled water recovered
slowly and was still pretty acidic even after the added calcium carbonate was added.
Ocean water contains natural buffers before the added calcium carbonate already, so the
added calcium carbonate made the process a lot faster than the distilled water with less
natural buffers available.
5. Do you feel that the balloon experiment is a valid model for ocean absorption of
CO2? Explain your answer.
I think that the balloon experiment is a valid model for ocean absorption of CO2 because
it is a good way to see how the natural buffers in ocean water can quickly reverse the
effects of CO2 rather than the distilled water, which has less natural buffers. My results
do not support my hypothesis, through my experiment I found that with added CO2,
ocean water pH will become more acidic quicker than distilled water.
CITATIONS:
"Ocean Acidification from Domestic to International." News Watch. N.p., n.d.
Web. 03 Sept. 2014.