Upper level biogeochemistry course.

Basic knowledge of chemical equilibria among dissolved inorganic carbon species in aqueous systems and charge balance equations.

Give students some understanding how natural precipitation pH varies as a function of atmospheric CO2, and I put this into context of discussion on sources of acidity of acid rains in northeast US. Could be used as a stand-alone exercise.

Chemical composition of rain, and general controls on natural water chemistry

This exercise involves looking for equilibrium constants for important inorganic carbon reactions.

Working in groups

Using 1 bar total atmospheric pressure, 25oC, and pCO2=10^-3.5 bar as an initial condition, students will write down chemical reactions that dissolve CO2 and H2CO3, which further dissociates into protons and bicarbonate. Then students will look for data for equilibrium constants for these reactions and calculate the pH of the final solution.

Then do the same calculation again when atmospheric CO2 concentration doubles and compare pH values in two scenarios.

This back of the envelope calculation helps us to discuss also the impacts of rising CO2 levels on climate change and ocean acidification.

I will bring a volunteer group to the white board and ask them to explain how they have done the calculation. Then students can compare notes and know where they might have done wrong.

I use two books for reference and resources:

The geochemistry of natural waters by James I. Drever

Aqueous Environmental Geochemistry by Donald Langmuir.