Final answer:
The buffering ion in sea water is HCO3- (bicarbonate), which helps maintain stable pH levels by reacting with acids and bases and combines with calcium to form calcium carbonate in marine organisms.
Step-by-step explanation:
The ion in seawater that serves as a buffer is HCO3- (bicarbonate). Bicarbonate acts as a buffer by reacting with acids and bases to maintain a stable pH level. In seawater, bicarbonate ions combine with calcium to form calcium carbonate (CaCO3), a vital component of marine organism shells. This buffering action is essential to ocean chemistry and marine life. Bicarbonate ions are also a crucial part of the bicarbonate-carbonic acid buffer system in human blood, which regulates blood pH and is managed by sodium ions. The bicarbonate buffer system works as follows: when sodium bicarbonate (NaHCO3) encounters a strong acid, carbonic acid (H2CO3), a weak acid, is formed; conversely, when carbonic acid faces a strong base like NaOH, bicarbonate and water are produced, thus maintaining homeostasis.