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Carbon dioxide and the acidification of our oceans

Elementary school
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Science Project Description

Carbon dioxide and the acidification of our oceans
This experiment was performed to find out the effect of carbon dioxide on the pH level of water. Human activities such as deforestation and the burning of fossil fuel increases the level of carbon dioxide in our atmosphere. The results of this experiment will show the effects of an increased carbon dioxide level on our oceans' acidity levels.

Project Info

Complexity level:3
Project cost ($):5
Time required:1 hour to prepare, 2 hours for experiment
Material availability:Easily found
Safety concerns: 1. Be careful not to inhale the smoke from the exhaust. If inhaled it can cause dizziness and carbon monoxide poisoning. 2. Adult participation is required when working with the car.


Increasing levels of carbon dioxide lowers the pH of water, making it more acidic.


Greenhouse gasses

Since the industrial revolution 250 years ago (approx. 1750s), the surge in industrial activities has resulted in an increase of the release of pollution gases into our atmosphere. Through industrialization, we have created machines and vehicles that consume fossil fuel and release these harmful gases into our atmosphere.

These harmful gases are called"greenhouse gases" and they comprise chiefly of carbon dioxide, water vapor, ozone and methane. Over the years, the carbon dioxide levels in our atmosphere have increased from 280 parts per million to about 380 parts per million presently. The main contributors to this trend are human activities such as deforestation and the burning of fossil fuel. This discharge of waste or by-products due to human activity is called the"anthropogenic effect".
The two main problems caused by greenhouse gases are global warming and ocean acidification.

Ocean acidification

As mentioned above, the anthropogenic effect results in the increase of carbon dioxide in the atmosphere. Part of this carbon dioxide is absorbed by our oceans. This process lowers the pH levels of the oceans. Over the years, the pH levels of our oceans is estimated to have dropped from 8.18 to 8.10. If this process continues, the ocean will gradually become more acidic.

With the acidificaton of our oceans, marine life will find it increasingly difficult to survive. Already, the lowering of pH levels and increased ocean temperatures have destroyed and killed up to 80% of the corals in the world. Coral reef destruction is a big indicator of the magnitude of this worrying trend.

Scientific Terms

Anthropogenic, greenhouse gas, ocean acidification, global warming


The materials required for this experiment:

  • 1 liter empty water bottle
  • Tap water
  • About 300 mm length of rubber hose between 15-20mm in diameter
  • 1 meter length of rubber hose between 15-20mm in diameter
  • 1 air-tight plastic bag
  • pH paper
  • stop watch
  • masking tape
  • car which runs on gasoline 


  1. For this experiment, the independent variable is the concentration of the carbon dioxide- which differs between the concentration of CO2 in the air expelled from our lungs versus the concentration of CO2 contained in the smoke from a car exhaust. The dependent variable is the level of acidity in the water. This is determined by measuring using a pH paper. The constants (control variables) are the type of water used (i.e. tap water, sea water etc), the amount of water and the time air is forced/blown into the water.
  2. The water bottle is filled with 1 liter of tap water.
  3. Take a pH reading of the water. Record the result in the table below.
  4. Insert one end of the 300mm of rubber hose into the water in the bottle. Blow air through the tube and observe air bubbles rising from the tube through the water. Continue blowing for 3 minutes.
  5. At the 3 minute mark, take a pH reading of the water. Record the result in the table below.
  6. The water in the bottle is replaced with new tap water.
  7. Fit a plastic bag around the exhaust pipe of a car. Fit it so that if air was to be expelled from the exhaust pipe, the bag would inflate. Secure the bag around the exhaust pipe with masking tape.
  8. Make a small hole at the other end of the plastic bag and insert the 1 meter hose to a depth of about 5 cm. Secure the hose with masking tape.
  9. Insert the free end of the hose into the water in the bottle. Start the car and watch the bag inflate and observe air bubbles rising from the tube through the water. Allow the bubbles to rish through the water for 3 minutes.
  10. At the 3 minute mark, take a pH reading of the water. Record the result in the table below.
  11. The human lung has about 4% carbon dioxide whereas the smoke from the car exhaust will have about 12% carbon dioxide. 


The result show that increasing the level of carbon dioxide in the water-filled bottle will lower the pH of the water making it more acidic.


The hypothesis that increasing the level of carbon dioxide in water will lower the pH level of the water, thus making it more acidic, is proven to be true. The acidity of the water increased when a higher concentration of carbon dioxide was used.

The increasing acidity of our oceans is a growing concern. Our growing dependence on fuels leads to the creation of many greenhouse gases. With increasing ocean acidity, scientists have proven that much of marine life is at risk. The sea is a bountiful source of food for humans and other animals. If the delicate balance in the ecology of marine life is toppled, there will be knock-on effect on the rest of the earth's human and animal population.

Conserve energy by taking public transportation instead of driving a car. Switch off lights when you leave your room and encourage your parents to purchase energy-efficient products. Do your part to conserve energy for even a little bit of effort will go a long way to helping stem the rise of the greenhouse effect, if we all play our part.

Also consider

This experiment can also be done by using sea water instead of tap water.

Try to modify this experiment by increasing the time the air bubbles are blown and see if the results are different.

Think of ways to rebalance the pH of the water. What can you add to the water to make it less acidic? Consider if there will be by-products in this neutralizing process. Would neutralizing the water turn out to be more harmful than good? 


  • Greenhouse gas -
  • Ocean acidification -

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