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.