It is best to use water that has been boiled and then cooled. This lessens the amount of calcium carbonate in the water, which can slow the process of acidification.

Activity steps - Blowing through water

1. Fill two clear cups two thirds full with water.
2. Take a drinking straw and blow through the water of one of the cups. This bubbles the carbon dioxide from exhaled breath through the water.
3. Taking a rest every 15 seconds, blow for 2 to 3 minutes through the water.
4. Before pouring your red cabbage indicator into each of the cups, try to predict how the colour of the indicator may change. Hint: the red cabbage indicator will turn pinker if the water is more acidic and bluer if the water is less acidic.
5. Pour 50ml of red cabbage water into each cup and observe the difference between the water in the two cups.

If you want to see a more dramatic difference between two cups of water, try this method.

Activity steps - Using still and sparkling water

1. Fill one clear cup with tap water and one with sparkling water.
2. Before pouring your red cabbage indicator into each of the cups, try to predict how the colour of the indicator may change. Hint: the red cabbage indicator will turn pinker if the water is more acidic and bluer if the water is less acidic.
3. Pour 50ml of red cabbage water into each cup and observe the difference between the water in the two cups.

• 2 clear plastic cups
• Drinking straw
• pH indicator *
• Tap water
• Sparkling mineral water (optional)

* We suggest red cabbage indicator because you can make it at home by boiling up red cabbage in a little water. Be aware that this can get a little smelly so make sure to open a window. Make sure that the red cabbage water is cooled before it is handled by children. You can also use other pH indicators, such as store-bought indicator for testing water which is usually available from pet stores.

The other carbon problem

Ocean acidification is also known as the other carbon problem. It is the process by which carbon dioxide (CO₂) in the atmosphere dissolves in the upper waters of the ocean (H₂O) and through a chemical reaction becomes carbonic acid (H₂CO₃).

This increased acidity decreases the amount of carbonate ions available in the ocean. Many living things rely on carbonate to build body structures. Coral polyps use carbonate to create little 'cups' that they live in and use as protection from predators. Crustaceans, such as prawns or lobsters, and molluscs, such as clams and scallops, also rely on carbonate to build their exoskeletons, or 'shells'.

Lower levels of carbonate in the ocean means that coral polyps and other living things need to expend more energy taking what is left to create coral reefs and shells. As more energy is spent on building structures, less energy is available for other processes such as reproduction and growth and can even led to starvation. Ocean acidification happens in all areas of the oceans and may have ripple effects on ocean health.