Question
Aluminium hydroxide and ranitidine can be used to relieve indigestion.
(a) (i) Write an equation for the reaction of aluminium hydroxide with stomach acid.
(ii) Calculate the mass, in g, of aluminium hydroxide needed to neutralize 100.0\(cm^3\) of \(5.00 × 10^{-3}\) mol \(dm^{-3}\) stomach acid.
(b) Explain how ranitidine (\(Zantac^®\)) can also relieve excess stomach acid.
Answer/Explanation
Answer:
(a) (i) \(Al(OH)_3(s)+ 3HCl(aq) \rightarrow AlCl_3(aq) + 3H_2O(l)\)
OR
\(Al(OH)_3(s) + 3H+(aq) \rightarrow Al^{3+}(aq) + 3H_2O(l)\)
(ii) «100 \(cm^3\) / 1000 \(cm^3\) x \(5.00×10^{-3}\) mol \(dm^{-3}\) = » \(5.00×10^{-4}\) «mol HCl»
«\(5.00×10^{-4}\) mol HCl /3 x 78.01 g \(mol^{-1}\) \(Al(OH)_3\) = » 0.0130 «g \(Al(OH)_3\)»
(b) blocks/binds to H2/histamine receptors «in cells of stomach lining»
OR
prevents histamine binding to H2/histamine receptors «and triggering acid
secretion»
prevents «parietal cells from» releasing/producing acid
Question
Magnesium carbonate and aluminium hydroxide are two antacids.
(a) Write two equations showing how these antacids neutralize excess hydrochloric acid.
Magnesium carbonate:
Aluminium hydroxide:
(b) Show by calculation that a 2.00g tablet of aluminium hydroxide would neutralize more hydrochloric acid than a 2.00g tablet of magnesium carbonate.
Answer/Explanation
Answer:
\(MgCO_3(s) + 2HCl(aq) → MgCl_2(aq) + H_2O(l) + CO_2(g)\)
AND
\(Al(OH)_3(s) +3HCl(aq)→ AlCl_3(aq) + 3H_2O(l)\)
(b) «\(n(MgCO_3)\) = 2.00g/84.32g \(mol^{-1}\) =» 0.0237« mol»
AND
«\(n(Al(OH)_3)\) = 2.00g/78.01g \(mol^{-1}\) =» 0.0256 «mol»
«0.0237\(n(MgCO_3)\) × 2 =» 0.0474 «n(HCl) neutralised»
AND
«0.0256 \(n(Al(OH)_3)\) × 3 =» 0.0768 «n(HCl) neutralised»
Question
Mild heartburn is treated with antacids such as calcium carbonate.
a. Formulate an equation for the neutralization of stomach acid with calcium carbonate, $\mathrm{CaCO}_3(\mathrm{~s})$.
b. 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:
▶️Answer/Explanation
Markscheme
a. $\mathrm{CaCO}_3(\mathrm{~s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{CO}_2(\mathrm{~g})+\mathrm{CaCl}_2(\mathrm{aq})+\mathrm{H}_2 \mathrm{O}(\mathrm{l}) \quad[\boldsymbol{\sim}]$
Note: Accept balanced ionic equations involving ” $\mathrm{H}^{+}$” or ” $\mathrm{H}_3 \mathrm{O}^{+ \text {“. }}$
Do not accept ” $\mathrm{H}_2 \mathrm{CO}_3$ “.
b. Omeprazole:
inhibits enzyme/«gastric» proton pump «which secretes $\mathrm{H}^{+}$ions into gastric juice»
OR
inhibits the $\mathrm{H}^{+} / \mathrm{K}^{+}$-ATPase system [ [ ]
Ranitidine:
inhibits/blocks $\mathrm{H}$ /histamine receptors «in cells of stomach lining»
OR
prevents histamine binding to $\mathrm{H} 2$ /histamine receptors «and triggering acid secretion» [
Note: Accept “H2-receptor antagonist” for M2.