| Date | May 2019 | Marks available | 1 | Reference code | 19M.3.sl.TZ1.16 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Formulate | Question number | 16 | Adapted from | N/A |
Question
Mild heartburn is treated with antacids such as calcium carbonate.
Formulate an equation for the neutralization of stomach acid with calcium carbonate, CaCO3 (s).
Determine the volume of CO2 (g), in dm3, produced at STP, when 1.00 g of CaCO3 (s) reacts completely with stomach acid.
Mr CaCO3 = 100.09
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:
Markscheme
CaCO3 (s) + 2HCl (aq) → CO2 (g) + CaCl2 (aq) + H2O (l) [✔]
Note: Accept balanced ionic equations involving “H+” or “H3O+”.
Do not accept “H2CO3”.
n CaCO3 = « =» 0.00999 «mol» [✔]
volume CO2 = «0.00999 mol × 22.7 dm3 mol–1 = » 0.227 «dm3» [✔]
Note: Accept 0.224 «dm3» if 22.4 dm3 mol–1 is used as molar volume.
Award [2] for correct answer.
Omeprazole:
inhibits enzyme/«gastric» proton pump «which secretes H+ ions into gastric juice»
OR
inhibits the H+/K+-ATPase system [✔]
Ranitidine:
inhibits/blocks H2/histamine receptors «in cells of stomach lining»
OR
prevents histamine binding to H2/histamine receptors «and triggering acid secretion» [✔]
Note: Accept “H2-receptor antagonist” for M2.
Examiners report
About two-thirds of the candidates could write an equation for the reaction of calcium carbonate with an acid. It was refreshing to find that “H2CO3” was only rarely encountered as a product.
It was encouraging that over half the students were able to calculate the volume of gas produced from a given mass of calcium carbonate.
Many students correctly remembered the modes of action of Omeprazole and Ranitidine, though needless to say a few confused these and weaker students thought they acted like conventional antacids.
Syllabus sections
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16N.3.sl.TZ0.19a:
Ranitidine (Zantac) is a drug that inhibits stomach acid production. Outline why the development of this drug was based on a detailed knowledge of the structure of histamine, shown below.
- 18N.3.sl.TZ0.14c: Suggest a technique for measuring the percentage mass of calcium carbonate in this type of...
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17N.3.sl.TZ0.20b:
The pH is maintained in different fluids in the body by the use of buffers.
Calculate the pH of a buffer solution of 0.0200 mol dm–3 carbonic acid, H2CO3, and 0.400 mol dm–3 sodium hydrogen carbonate, NaHCO3. The pKa of carbonic acid is 6.35.
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19M.3.hl.TZ2.23a(i):
Outline how ranitidine (Zantac) inhibits stomach acid production.
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17M.3.sl.TZ2.18a.i:
Compare and contrast the structures of oseltamivir and zanamivir, stating the names of functional groups.
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17N.3.sl.TZ0.20a:
Explain how ranitidine (Zantac) reduces stomach acid production.
-
16N.3.sl.TZ0.19b:
Two other drugs, omeprazole (Prilosec) and esomeprazole (Nexium), directly prevent the release of acid into the stomach. Identify the site of action in the body.
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17M.3.hl.TZ2.22a:
Outline how ranitidine (Zantac) functions to reduce stomach acidity.
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18M.3.sl.TZ2.18b:
Calculate the amount, in mol, of stomach acid neutralized by an antacid tablet containing 0.750 g calcium carbonate.
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19N.3.sl.TZ0.16a:
Identify the compound responsible for the acidity of gastric juice, and state whether it is a strong or weak acid.
-
18M.3.sl.TZ1.14b:
Explain how omeprazole (Prilosec) reduces stomach acidity.
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18N.3.sl.TZ0.14a:
Determine the pH of a buffer solution that is 0.0100 mol dm−3 sodium hydrogen carbonate and 0.0200 mol dm−3 sodium carbonate, using section 1 of the data booklet.
Ka (hydrogen carbonate ion) = 4.8 × 10−11
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17M.3.sl.TZ2.17a:
Two drugs are ranitidine (Zantac) and omeprazole (Prilosec). Outline how they function to reduce stomach acidity.
- 19N.3.sl.TZ0.16c: Outline how ranitidine reduces stomach acidity.
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19M.3.sl.TZ2.16a(ii):
Outline two advantages of taking ranitidine instead of an antacid which neutralizes excess acid.
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19N.3.sl.TZ0.16d:
Calculate the pH of a buffer solution which contains 0.20 mol dm−3 ethanoic acid and 0.50 mol dm−3 sodium ethanoate. Use section 1 of the data booklet.
pKa (ethanoic acid) = 4.76
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16N.3.sl.TZ0.19c:
A different approach to treating excess stomach acid is to neutralize it with antacids. Formulate an equation that shows the action of an antacid that can neutralize three moles of hydrogen ions, H+, per mole of antacid.
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19M.3.sl.TZ1.16a(ii):
Determine the volume of CO2 (g), in dm3, produced at STP, when 1.00 g of CaCO3 (s) reacts completely with stomach acid.
Mr CaCO3 = 100.09
-
19M.3.sl.TZ2.16b:
Some antacids contain carbonates.
Determine the pH of a buffer solution which contains 0.160 mol dm−3 CO32− and 0.200 mol dm−3 HCO3−, using section 1 of the data booklet.
pKa (HCO3−) = 10.32
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18N.3.sl.TZ0.14b:
State the equation for the reaction of calcium carbonate, the active ingredient in some antacids, with stomach acid.
-
18M.3.sl.TZ2.18a:
Formulate a chemical equation for the neutralization of stomach acid with calcium carbonate.
-
18M.3.sl.TZ1.14a.ii:
Determine the amount, in mol, of hydrochloric acid neutralized by one antacid tablet.
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19N.3.sl.TZ0.16b:
An antacid contains calcium carbonate and magnesium carbonate.
Write the equation for the reaction of magnesium carbonate with excess stomach acid.
-
19M.3.hl.TZ1.21a:
Formulate an equation for the neutralization of stomach acid with calcium carbonate, CaCO3 (s).
-
17M.3.sl.TZ2.17b:
0.500 g of solid anhydrous sodium carbonate, Na2CO3(s), is dissolved in 75.0 cm3 of 0.100 moldm−3 sodium hydrogen carbonate solution, NaHCO3(aq). Assume the volume does not change when the salt dissolves.
HCO3−(aq) CO32−(aq) + H+(aq) pKa = 10.35.
Calculate the pH of the buffer solution.
-
19M.3.hl.TZ2.23a(ii):
Outline two advantages of taking ranitidine instead of an antacid which neutralizes excess acid.
-
19M.3.hl.TZ2.23b:
Some antacids contain carbonates.
Determine the pH of a buffer solution which contains 0.160 mol dm−3 CO32− and 0.200 mol dm−3 HCO3−, using section 1 of the data booklet.
pKa (HCO3−) = 10.32
-
18M.3.sl.TZ2.18c:
Explain how omeprazole (Prilosec) regulates pH in the stomach.
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17M.3.sl.TZ2.18a.ii:
Deduce the wavenumber of one absorbance seen in the IR spectrum of only one of the compounds, using section 26 of the data booklet.
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18M.3.sl.TZ1.14a.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.
-
17M.3.sl.TZ1.20a:
Calculate the pH of the buffer from the following data and section 1 of the data booklet.
pKa(CO2) = 6.34
[HCO3−(aq)] = 1.40 × 10−2 moldm−3
[CO2(aq)] = 1.25 × 10−3 moldm−3
-
17M.3.sl.TZ1.20b:
Explain the effect of a large amount of aspirin on the pH of blood.
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19M.3.hl.TZ1.21b:
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:
-
19M.3.sl.TZ2.16a(i):
Outline how ranitidine (Zantac) inhibits stomach acid production.
-
19M.3.sl.TZ1.16b:
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:
