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Date November 2020 Marks available 3 Reference code 20N.3.sl.TZ0.12
Level SL Paper 3 Time zone TZ0
Command term Show Question number 12 Adapted from N/A

Question

Consider the following antacids:

Show that antacid X is more effective, per tablet, than antacid Y.

Markscheme

same reactant mole ratio «in both equations»
OR
Mg(OH)2(s)+2HCl(aq)«→MgCl2(aq)+2H2O(l)» AND
CaCO3(s)+2HCl(aq)«→CaCl2(aq)+H2O(l)+CO2(g)» ✔


Mg𝑛(OH)2=«0.20058.32=»3.43×10−3«mol» AND
CaCO3𝑛=«0.220100.09=»2.20×10−3«mol» ✔

«tablet of» X neutralizes 6.86×10−3«mol» HCl AND «tablet of» Y neutralizes 4.40×10−3«mol» HCl ✔

Award [3] for correct final statement AND values in M3.

Examiners report

Very poorly answered. Many students scored at least 1 point. This was usually M2 by determining the mols
of each antacid present. However, many students totally ignored the corresponding balanced chemical equations or entered wrong ones. A worrying number of candidates didn't therefore use the correct molar ratio to calculate the values in M3. Showing the calculations and how X is more effective than Y was the point of the question.

Syllabus sections

Options » D: Medicinal chemistry » D.1 Pharmaceutical products and drug action
Core » Topic 1: Stoichiometric relationships » 1.2 The mole concept
Core » Topic 1: Stoichiometric relationships
Options » D: Medicinal chemistry
Core
Options

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