Why does an increase in alkalinity raise the sample's pH?

Document ID

Document ID TE115

Published Date

Published Date 27/05/2017
Question
Why does an increase in alkalinity raise the sample's pH?
Summary
The relationship between alkalinity and pH
Answer
Alkalinity can increase the pH of the sample, making it more basic, when the alkalinity comes from a mineral source such as calcium carbonate (CaCO3). When CaCO3 dissolves in water, the carbonate (CO32-) can react with water to form bicarbonate (HCO3-), which produces hydroxide (OH-):

CaCO3 (s) -> Ca2+ + CO32-
CO32- + H2O -> HCO3- +OH-

The hydroxide ion (OH-) is a strong base. An increase in OH- concentration will cause the pH to increase.