DP Chemistry (last assessment 2024)

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Question 23M.3.SL.TZ2.18

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Date May 2023 Marks available [Maximum mark: 5] Reference code 23M.3.SL.TZ2.18
Level SL Paper 3 Time zone TZ2
Command term Calculate, Explain, Write Question number 18 Adapted from N/A
18.
[Maximum mark: 5]
23M.3.SL.TZ2.18

Aluminium hydroxide and ranitidine can be used to relieve indigestion.

(a.i)

Write an equation for the reaction of aluminium hydroxide with stomach acid.

[1]

Markscheme

Al (OH)3 (s)+ 3HCl (aq) → AlCl3 (aq) + 3H2O (l)

OR

Al (OH)3 (s) + 3H+ (aq) → Al3+ (aq) + 3H2O (l) ✓

(a.ii)

Calculate the mass, in g, of aluminium hydroxide needed to neutralize 100.0 cm3 of 5.00 × 10−3 mol dm−3 stomach acid.

[2]

Markscheme

«100 cm3 / 1000 cm3 × 5.00 × 10−3 mol dm−3 = » 5.00 × 10−4 «mol HCl» ✓

«5.00 × 10−4 mol HCl /3 × 78.01 g mol−1 Al(OH)3 = » 0.0130 «g Al(OH)3» ✓

 

Award [2] for correct final answer.

(b)

Explain how ranitidine (Zantac®) can also relieve excess stomach acid.

[2]

Markscheme

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 ✓

 

Do not accept “antihistamine” by itself.

Accept “H2-receptor antagonist/H2RA”
OR
“blocks/inhibits action of histamine” for M1.

Do not accept “blocks receptors” alone for M1.

Do not accept “proton pump/ATPase inhibitor”.