Why Should We Care?

The pH scale is very useful because hydronium ion concentrations can vary dramatically, sometimes by factors on the order of 10¹⁴. The pH scale allows these ion concentrations to be expressed in a more convenient manner. For instance, rather than expressing the acidity of solutions as a range between [H₃O⁺]=1.0 mol L^-1 and [H₃O⁺]=1.0×10-14 mol L^-1, the acidity of these solutions can simply be expressed by a pH between 0 and 14 (for some highly acidic or basic solutions, the pH may even be outside of this range).

Also, the pH scale can be easily applied to analyze the acidity or basicity of the ocean. As you have learned earlier, the ocean is naturally basic, with a current pH value of about 8.05. However, the pH of the ocean has been decreasing. Open the Ocean Trends Learning Tool to explore the data that helped scientists realize that the pH of the ocean was changing.

Click the box beside 'proxy pH' at the bottom of the window to observe how pH has changed since 1989. You can use the slope tool on the left hand side of the window to calculate the rate at which ocean pH has changed. Simply click the 'proxy pH' tab on the left side of the Learning Tool and then click and drag the cursor across the graph.

Your Turn

As shown in the Ocean Trends Learning Tool, how has the pH of the ocean changed over the last 20 years? At what rate has the pH changed from 1989 to 2010? Express your answer in pH units per year.

Question For Thought

In the Ocean Trends Learning Tool display the data for 'proxy pH' and 'atmospheric carbon dioxide'. How do the slopes of atmospheric carbon dioxide concentration and surface ocean pH compare? What is the correlation between atmospheric carbon dioxide concentrations and ocean pH?