An antacid tablet contains 680 mg of calcium carbonate, CaCO₃, and 80 mg of magnesium carbonate, MgCO₃.

State the equation for the reaction of magnesium carbonate with hydrochloric acid.

Determine the amount, in mol, of hydrochloric acid neutralized by one antacid tablet.

Explain how omeprazole (Prilosec) reduces stomach acidity.

MgCO₃(s) + 2HCl(aq) → CO₂(g) + H₂O(l) + MgCl₂(aq)

Do not accept “H₂CO₃”.

[1 mark]

n(HCl) = 2 n(CaCO₃) + 2 n(MgCO₃)

OR

n(HCl) = \(\frac{{2 \times 0.680\;\ll {\text{g}}\gg }}{{100.09\;\ll {\text{g mo}}{{\text{l}}^{ - 1}}\gg }} + \frac{{2 \times 0.080\;\ll {\text{g}}\gg }}{{84.32\;\ll {\text{g mo}}{{\text{l}}^{ - 1}}\gg }}\)

«n(HCl) = 0.0136 mol + 0.0019 mol =» 0.016 «mol»

Award [2] for correct final answer.

Award [1 max] for correctly calculating amount of acid neutralized by just CaCO₃ (0.014 «mol») or MgCO₃ (0.002 «mol»).

[2 marks]

inhibits the secretion of stomach acid/H⁺

«active metabolites» bind «irreversibly» to «receptors of the» proton pump

Accept “PPI/proton pump inhibitor”.

Do not award mark for “binds to H2/histamine receptors”. (Ranitidine mode of action.)

Accept “H⁺/K⁺ ATPase” for “proton pump”.

[2 marks]