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Acidic Oceans

Increased carbon dioxide in the ocean makes sea water more acidic and this affects organisms that live in it.

Australian Curriculum links

  • Science >Earth and Space Sciences > Year 4 > ACSSU075
  • Science > Chemical Sciences > Year 6 > ACSSU095
  • Science > Earth and Space Sciences > Year 7 > ACSSU116
  • Science > Nature and Development of Science > Year 7 > ACSHE223
  • Science > Chemical Sciences > Year 9 > ACSSU179
  • Science >Earth and Space Sciences > Year 10 > ACSSU189

You’ll need

  • 2 pieces of egg shell
  • Vinegar
  • Clear plastic cup

Try this

  1. Use Blu Tack and a piece of egg shell to make a sea creature with a shell (e.g. snail, crab, clam). Place the creature in the cup and cover with vinegar. Leave for 10 minutes. What is happening to the shell?
  2. Pull the creature out, remove the shell and break it in half.
  3. Now take a piece of egg shell that was not put in vinegar and break it in half. Was one piece of egg shell harder to break than the other?

Further investigation

  • Try putting the shell or a whole raw egg in the vinegar overnight

What’s happening?

Vinegar contains acetic acid, which makes it acidic. The egg shell contains calcium carbonate, which makes it slightly alkaline.

When the vinegar is added to the egg shell they react. This reaction between the shell and vinegar dissolves the egg shell and produces bubbles of carbon dioxide.

When carbon dioxide is absorbed by the ocean, it makes sea water more acidic.

The pH of a solution indicates how much acid is present in it. A lower pH means more acid is present. The pH of vinegar is about 2.4. Sea water has a pH of 8.1, but the ocean is becoming more acidic and the pH has dropped 0.1 units since humans started emitting large amounts of carbon dioxide.

While this may not sound like much, it actually means that there is a lot more acid in the water. It is predicted that over the next 100 years the pH will continue to fall to between 7.8 and 7.9. This change means there will be 30% more acid molecules in sea water.

This increase in acidity will affect many plants and animals that live in the ocean. Animals that use calcium to build their skeletons like star fish and molluscs will find it harder to get extract calcium from the water. If the ocean becomes too acidic, it will start to dissolve the shells of animals living in it. If their shells weaken they may not be able to survive.