DP Chemistry (last assessment 2024)

Question 18M.3.sl.TZ2.18

Date	May 2018	Marks available	[Maximum mark: 4]	Reference code	18M.3.sl.TZ2.18
Level	sl	Paper	3	Time zone	TZ2
Command term	Calculate, Explain, Formulate	Question number	18	Adapted from	N/A

18.

[Maximum mark: 4]

18M.3.sl.TZ2.18

Excess acid in the stomach is often treated with calcium carbonate.

(a)

Formulate a chemical equation for the neutralization of stomach acid with calcium carbonate.

[1]

Markscheme

2HCl(aq) + CaCO₃(s) → H₂O(l) + CO₂(g) + CaCl₂(aq)

Accept ionic equation:

2H⁺(aq) + CO₃^2–(aq) → CO₂(g) + H₂O(l)

[1 mark]

(b)

Calculate the amount, in mol, of stomach acid neutralized by an antacid tablet containing 0.750 g calcium carbonate.

[1]

Markscheme

« $\frac{{0.750 \times 2}}{{100.09}}$ =» 0.0150 «mol HCl»

[1 mark]

(c)

Explain how omeprazole (Prilosec) regulates pH in the stomach.

[2]

Markscheme

inhibits the secretion of stomach acid/H⁺

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

Do not accept “hydrogen/H/H₂” for “H⁺”.

Accept “PPI/proton pump inhibitor” for M2.

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

[2 marks]

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