DP Chemistry (last assessment 2024)

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Question 18M.3.sl.TZ1.14

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Date May 2018 Marks available [Maximum mark: 5] Reference code 18M.3.sl.TZ1.14
Level sl Paper 3 Time zone TZ1
Command term Determine, Explain, State Question number 14 Adapted from N/A
14.
[Maximum mark: 5]
18M.3.sl.TZ1.14

Excess stomach acid can be counteracted by a range of medications.

(a.i)

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.

[1]

Markscheme

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

 

Do not accept “H2CO3”.

[1 mark]

(a.ii)

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

[2]

Markscheme

n(HCl) = 2 n(CaCO3) + 2 n(MgCO3)

OR

n(HCl) =  2 × 0.680 ≪ g ≫ 100.09 ≪ g mo l − 1 ≫ + 2 × 0.080 ≪ g ≫ 84.32 ≪ g mo l − 1 ≫

 

«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]

(b)

Explain how omeprazole (Prilosec) reduces stomach acidity.

[2]

Markscheme

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]

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