Florida Drinking Water Operator "B" Practice Test

What effect does adding lime during the softening process have on bicarbonate alkalinity?

1. Increases acidity

2. Conversion to carbonate alkalinity

3. Reduces hardness

4. Neutralizes the solution

The correct answer is: Conversion to carbonate alkalinity

Adding lime during the softening process primarily results in the conversion of bicarbonate alkalinity into carbonate alkalinity. When lime (calcium hydroxide) is introduced into the water, it reacts with bicarbonate ions (HCO3-) present, leading to the release of carbon dioxide (CO2) and the formation of carbonate ions (CO3^2-). This reaction effectively transforms the bicarbonate alkalinity, which is the alkalinity measured as HCO3-, to carbonate alkalinity, measured as CO3^2-. The process plays an important role in water treatment, as it not only adjusts the pH of the water but also enhances the overall effectiveness of the softening process. As carbonate ions tend to precipitate with calcium and magnesium, this conversion is a crucial step in reducing hardness in the water supply. The other choices refer to different aspects of water chemistry that do not accurately describe the specific effect of adding lime during this process.