What type of ions are responsible for alkalinity in water?

Alkalinity in water is primarily associated with the presence of negative ions, specifically those that can neutralize acids. These ions typically include bicarbonate (HCO3-), carbonate (CO3^2-), and hydroxide (OH^-). These anions contribute to the buffering capacity of water, helping to maintain a stable pH by reacting with hydrogen ions (H+) when acids are introduced. This process is crucial in various natural and engineered water systems, as it influences aquatic life and the overall chemical balance in the environment.

Positive ions, on the other hand, such as sodium (Na+), calcium (Ca^2+), and magnesium (Mg^2+), contribute to total dissolved solids and electrical neutrality but do not directly affect alkalinity in the same way that negative ions do. Nonmetallic ions encompass a broader category and include both positive and negative ions, but it is the negative ions that specifically relate to alkalinity. Polyvalent cations are positively charged ions with a charge greater than one, and while they can influence water chemistry, they do not directly contribute to alkalinity.