<p>Calcium carbonate reacts with gastric acid to produce a salt and water. For calcium carbonate the postulated chemical reaction is: CaCO3&nbsp;+ 2HCl = CaCl2&nbsp;+ H2O + CO2<br />
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Two grams of calcium carbonate will readily bring 100 ml of hydrochloric acid to a pH above 6. The increase in gastric pH diminishes the activity of pepsin in the gastric secretion. Up to 30% of the oral calcium load may be absorbed.</p>