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Key Idea 5
Speciation and pH
Concept Question: What are acids and bases?

We have mentioned that various carbon species play a role in the acidification of the ocean. But what exactly do we mean when we talk about the speciation of an element?

The atoms of an element can be found in various compounds and molecules. For example, carbon atoms can be found as a part of CO2, H2CO3, HCO3-, CO32-, CaCO3 and a host of other compounds. Each of these compounds is a chemical species of carbon: they are unique entities that exist independently. Particles of the same species, however, are identical and have characteristic behaviors. The term speciation refers to the distribution of an atom, ion or molecule among the various forms or species in which the particle can be found. For instance, the speciation of carbon in the ocean refers to the distribution of carbon atoms among such forms as carbon dioxide, carbonic acid, hydrogen carbonate and other substances in the ocean that contain carbon atoms.