What does carbonate hardness (CH) represent?

Carbonate hardness (CH) primarily represents the concentration of bicarbonate ions (HCO3-) and carbonate ions (CO3^2-) that contribute to the hardness of water. In the context of water chemistry, hardness is typically associated with the presence of divalent cations like calcium (Ca2+) and magnesium (Mg2+), but carbonate hardness specifically focuses on the contribution from carbonate and bicarbonate species.

The bicarbonate ion plays a crucial role in buffering capacity and is significant in processes such as precipitation and dissolution of mineral salts in natural waters. CH is thus an essential concept as it helps to understand the alkalinity and buffering capacity of water, particularly in managing water quality for various applications, including drinking water and environmental monitoring.

Though calcium and magnesium ions are indeed involved in water hardness, they do not define carbonate hardness directly. Instead, they are part of the broader definition of total hardness, which includes both carbonate and non-carbonate hardness. Therefore, recognizing that carbonate hardness is primarily associated with bicarbonate compounds solidifies the understanding of its role in water chemistry.