By blowing air through water containing a pH indicator, students can observe how dissolved carbon dioxide lowers the pH of water, demonstrating the process of ocean acidification.

1. Fill two beakers with tap water.
2. Add several drops of a pH indicator (aquarium indicator, phenolphthalein or bromothymol blue) to each beaker.
3. To the first beaker, add a few drops of vinegar to show how an acid lowers pH (solution turns yellow).
4. Sprinkle baking soda into the same beaker to show how a base raises pH (solution turns blue).
5. Explain the indicator color changes in terms of acid–base reactions.
6. Blow gently through a straw into the second beaker for about 30 seconds.
7. Observe the color shift, indicating the water has become acidic due to dissolved carbon dioxide.

Ocean Acidification Demo - ElCheJaimito56:

📄 Ocean acidification - ABC Science: https://www.abc.net.au/science/articles/2011/02/24/3147423.htm

• Use different indicators, including aquarium indicator, phenolphthalein or bromothymol blue.
• Compare the effect of exhaled air with air from a balloon (ambient air) to highlight the role of CO₂ concentration.
• Use seawater samples instead of tap water to make the demonstration more realistic.

• Avoid ingesting indicator solution.
• Dispose of solutions safely in a sink with plenty of water.
• Blow gently through straws to prevent splashing.

• What gas in exhaled breath is responsible for lowering the water’s pH?
• How does the change in pH relate to what is happening in the oceans today?
• Why are organisms with calcium carbonate shells particularly vulnerable to ocean acidification?
• What is the difference between short-term pH changes in small systems (like a beaker) and long-term changes in the global ocean?
• Why is the rate of pH change in the oceans more concerning than the absolute pH level?