Bicarbonate alkalinity is caused by which species?

Bicarbonate alkalinity is caused by which species?

• A. Alkalinity Caused by CO3^2-
• B. Alkalinity Caused by HCO3-
• C. Alkalinity Caused by CaCO3
• D. Alkalinity Caused by CaCO3 and H2CO3

Answer: (B)

Alkalinity is the water’s capacity to neutralize acids, and in most natural waters this buffering comes from dissolved carbonate species. The bicarbonate form, HCO3−, is the main contributor to bicarbonate alkalinity because, over a wide pH range, carbon dioxide in water forms carbonic acid that predominantly exists as bicarbonate. When acid is added, bicarbonate reacts readily: HCO3− + H+ → CO2 + H2O, which buffers the solution and explains why bicarbonate is the key species for this type of alkalinity. Carbonate (CO3^2−) becomes important only at higher pH after further deprotonation of HCO3−, while hydroxide (OH−) contributes mainly in very basic conditions. Calcium carbonate (CaCO3) is a solid that can dissolve to release carbonate species, but the buffering action is due to the dissolved bicarbonate ions themselves. Therefore, bicarbonate alkalinity is caused by the bicarbonate ion, HCO3−.

Alkalinity is the water’s capacity to neutralize acids, and in most natural waters this buffering comes from dissolved carbonate species. The bicarbonate form, HCO3−, is the main contributor to bicarbonate alkalinity because, over a wide pH range, carbon dioxide in water forms carbonic acid that predominantly exists as bicarbonate. When acid is added, bicarbonate reacts readily: HCO3− + H+ → CO2 + H2O, which buffers the solution and explains why bicarbonate is the key species for this type of alkalinity. Carbonate (CO3^2−) becomes important only at higher pH after further deprotonation of HCO3−, while hydroxide (OH−) contributes mainly in very basic conditions. Calcium carbonate (CaCO3) is a solid that can dissolve to release carbonate species, but the buffering action is due to the dissolved bicarbonate ions themselves. Therefore, bicarbonate alkalinity is caused by the bicarbonate ion, HCO3−.