Question

Although the concentration of carbon dioxide in air and in most aquatic systems is similar, aquatic systems have an additional, more abundant, source of inorganic carbon that is lacking in the atmosphere. In the pH range typical of most natural bodies of water (6-9), which of the following represents this "additional" reservoir of inorganic carbon?

a) Carbon dioxide gas (CO2)
b) Bicarbonate ions (HCO3-)
c) Carbonate ions (CO32-)
d) Methane (CH4)
e) Oxygen gas (O2)

Answer 1

Aquatic systems have additional inorganic carbon sources, such as bicarbonate ions (HCO3-) and carbonate ions (CO32-). In a pH range of 6-9, typical for natural water bodies, bicarbonate ions are the predominant form, making them the 'additional' reservoir of inorganic carbon absent in the atmosphere.

Step-by-step explanation:

The question addresses the reservoirs of inorganic carbon in aquatic systems compared to the atmosphere, specifically in the context of the pH range typical of most natural bodies of water, which is between 6-9.

Aquatic systems, unlike the atmosphere, have additional reservoirs of inorganic carbon such as bicarbonate ions (HCO3-) and carbonate ions (CO32-).

When carbon dioxide (CO2) from the atmosphere dissolves in water, it reacts with water molecules and forms carbonic acid, which then dissociates into bicarbonate ions (HCO3-) and carbonate ions (CO32-). These ions represent an additional reservoir of inorganic carbon that is not present in the atmosphere.

At a typical natural water pH, the majority of this inorganic carbon is found as bicarbonate ions, making option b) Bicarbonate ions (HCO3-) the correct response to the student's question.

Additionally, bicarbonate ions in the ocean can combine with calcium to form calcium carbonate (CaCO3), which contributes to marine sediments and ultimately forms a significant carbon reservoir in limestone.