Mild heartburn is treated with antacids such as calcium carbonate.
Formulate an equation for the neutralization of stomach acid with calcium carbonate, CaCO3 (s).
a(i).
CaCO3 (s) + 2HCl (aq) → CO2 (g) + CaCl2 (aq) + H2O (l)
**Note:**Accept balanced ionic equations involving “H+” or “H3O+”.
Do not accept “H2CO3”.
a(i).
Determine the volume of CO2 (g), in dm3, produced at STP, when 1.00 g of CaCO3 (s) reacts completely with stomach acid.
Mr CaCO3 = 100.09
a(ii).
n CaCO3 = « 1.00 g 100.09 g mo l − 1 =» 0.00999 «mol»
volume CO2 = «0.00999 mol × 22.7 dm3 mol–1 = » 0.227 «dm3»
**Note:**Accept 0.224 «dm3» if 22.4 dm3 mol–1 is used as molar volume.
Award for correct answer.
a(ii).
Acid secretion can be regulated by other types of drugs such as omeprazole and ranitidine. Outline how each of these drugs acts to reduce excess stomach acid.
Omeprazole:
Ranitidine:
Omeprazole:
inhibits enzyme/«gastric» proton pump «which secretes H+ ions into gastric juice»
_OR
_inhibits the H+/K+-ATPase system
Ranitidine:
inhibits/blocks H2/histamine receptors «in cells of stomach lining»
OR
prevents histamine binding to H2/histamine receptors «and triggering acid secretion»
**Note:**Accept “H2-receptor antagonist” for M2.
