What main chemical is present when the pH of water reaches 10.2?

When the pH of water reaches 10.2, the primary species present is carbonate (CO3 -2). This occurs because as the pH increases, the chemistry of carbonates in water shifts toward the formation of carbonate ions.

At higher pH levels, carbonate ions become more predominant as the equilibrium between carbonic acid, bicarbonate, and carbonate shifts in favor of the latter. The relationship between these species can be described by the following equilibrium reactions:

1. Carbonic acid (H2CO3) can dissociate into bicarbonate (HCO3-) and hydrogen ions (H+).
2. Bicarbonate can further dissociate into carbonate ions (CO3 -2) and hydrogen ions (H+).

As the pH increases and less hydrogen ions are present (a condition indicative of basicity), more carbonate ions will be generated from the bicarbonate. This chemical behavior is crucial in understanding water chemistry, especially in contexts like water treatment, where controlling pH is essential for managing carbonate species and their effects on water quality.

In contrast, hydroxide (OH) ions do exist at this pH level, but they are a result of the ionization of water and not the main species affecting the equilibrium of