At a pH of 8.3, what is the main chemical present in the water?

At a pH of 8.3, the main chemical present in the water is bicarbonate (HCO3). This specific pH level indicates an alkaline condition, where the equilibrium between carbon dioxide, bicarbonate, and carbonate species is dominated by bicarbonate.

In natural waters, carbon dioxide exists in equilibrium with bicarbonate and carbonate, following the acid-base equilibrium reactions. As the pH increases, bicarbonate becomes a more prevalent species due to the following reactions:

1. Carbon dioxide (CO2) dissolves in water to form carbonic acid (H2CO3).
2. Carbonic acid can dissociate into bicarbonate (HCO3) and hydrogen ions (H+).
3. Bicarbonate can further dissociate into carbonate (CO3-2) and another hydrogen ion (H+), but this process is favored at higher pH levels (above 9).

At a pH value of approximately 8.3, the predominant form for carbonate species is bicarbonate. Therefore, it is accurate to say that at this pH, bicarbonate is the main chemical present, making it essential for understanding the buffering capacity of natural waters and their responses to changes in pH.