Is calcium carbonate a base or alkali?

Answer 1

It is a base, and this is why it is put in anti acid medication. It reacts with acids in what is known as a neutralization reaction. Now, it is not an extremely strong base (like some hydroxides), but it effectively does the job needed for indigestion.

Answer 2

Calcium carbonate is a base because it can accept protons (H+) to neutralize acids, but it is not considered an alkali because it does not dissolve in water to release hydroxide ions (OH-) like traditional alkalis such as sodium hydroxide.