These data shows that atmospheric carbon dioxide and the pH of the surface layer of the ocean are inversely correlated; as atmospheric carbon dioxide concentrations increase, the pH of the ocean decreases. But will further increases in atmospheric carbon dioxide cause the ocean pH to decrease? After all, correlation does not necessarily equal causation.
A simple experiment can be conducted to determine if increased concentrations of dissolved carbon dioxide change the pH of a solution. Watch the video below to see what happens when carbon dioxide is bubbled through water colored with a universal pH indicator. Before watching the video, refer to the example pH indicator strip to predict what will happen to the indicator in the water as carbon dioxide is bubbled through it.
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As carbon dioxide is bubbled through the water, some of the gaseous carbon dioxide dissolves in the the water. Evidently, greater concentrations dissolved carbon dioxide cause the pH of water to decrease. You can also perform a virtual version of this experiment using the pH Indicator Learning Tool. As you adjust the concentration of hydronium ions using the slider bar, how does the pH respond? How does the color of the indicator in the water change?
Your Turn
Experiments indicate that increasing concentrations of dissolved carbon dioxide in the ocean result in a lowered ocean pH. Using the pH Indicator Learning Tool, what is the color of the indicator in the solution when hydronium ion concentrations are low? When hydronium ion concentrations are high? What is the pH when hydronium ion concentrations are high?
When hydronium ion concentrations are low, the solution is a dark grey color. When hydronium ions concentrations are high, the solution becomes yellow. When hydronium ion concentrations are high, the pH of the solution is low.