Alkalinity in Natural Water

Introduction:
Alkalinity is an important parameter used to measure the buffering capacity of water. It refers to the ability of water to neutralize acids and maintain its pH level. The major contributors to alkalinity in natural water are hydroxyl, carbonate, and bicarbonate ions.

Explanation:
The correct answer is option B, which states that the major portion of alkalinity in natural water is caused by hydroxyl, carbonate, and bicarbonate ions. Let's understand why this is the case:

Hydroxyl ions (OH-):
- Hydroxyl ions are formed when water dissociates into its constituent ions, H+ and OH-.
- The concentration of hydroxyl ions in natural water is relatively low compared to carbonate and bicarbonate ions.
- Therefore, hydroxyl ions contribute to the alkalinity of water but are not the major component.

Carbonate ions (CO3^2-):
- Carbonate ions are formed when carbon dioxide dissolves in water, and the dissolved carbon dioxide reacts with water to form carbonic acid (H2CO3).
- Carbonic acid then dissociates into bicarbonate ions (HCO3-) and carbonate ions (CO3^2-).
- Bicarbonate ions can further dissociate to form hydroxyl ions and carbon dioxide.
- Carbonate ions contribute significantly to the alkalinity of water and play a major role in buffering pH changes.

Bicarbonate ions (HCO3-):
- Bicarbonate ions are the most abundant and important contributors to water alkalinity.
- They are formed from the dissociation of carbonic acid (H2CO3) and can also be formed from the dissolution of carbonate minerals.
- Bicarbonate ions act as a chemical buffer, helping to maintain the pH of water within a certain range.

Conclusion:
In summary, the major portion of alkalinity in natural water is caused by the presence of hydroxyl, carbonate, and bicarbonate ions. These ions contribute to the water's buffering capacity and help maintain pH levels. Understanding the sources and composition of alkalinity is crucial for various applications, including water treatment, environmental monitoring, and aquatic ecosystem management.