How is alkalinity expressed in milligrams per liter as CaCO3?

Alkalinity is a measure of the capacity of water to neutralize acids, and it is commonly expressed in terms of calcium carbonate (CaCO3). This expression is used because CaCO3 is a standard reference point for measuring alkalinity in water chemistry.

The correct answer details how to convert the concentration of a specific species that contributes to alkalinity, such as bicarbonate (HCO3^-), carbonate (CO3^2-), or hydroxide (OH^-), into an equivalent concentration expressed as CaCO3. The formula includes using the equivalent weight (EW) of CaCO3 alongside the equivalent weight of the species in question. The equivalent weight is calculated based on the molar mass and the number of moles of reactive or ionizable hydrogen in the species.

By multiplying the concentration of the species in mg/L by the ratio of the equivalent weight of CaCO3 to that of the species, you obtain the concentration of alkalinity expressed in mg/L as CaCO3. This proportionality ensures that the contribution of different species to alkalinity can be accurately compared and quantified on a standardized basis. Thus, it allows for a consistent understanding of the alkalinity in various water samples based on their specific chemical compositions.