Chemistry 12 (SL + HL)
Unit 6 / IB Topic D2
Medicines and Drugs - Part 2
Antacids
HOW THE STOMACH WORKS
Links:
http://www.youtube.com/watch?v=URHBBE3RKEs
http://www.youtube.com/watch?v=uFX-MOLSGaU&feature=related
•
Most tissues and fluids in your body have a pH near the neutral value of 7
•
Your stomach, however, is a different story. The fluids inside your stomach have a pH as low as 1-2
This low pH value is the result of the normal action of cells in the lining of the stomach which produce
hydrochloric acid (HCl)
•
Why is the stomach naturally acidic?
1.
Low pH levels destroy bacteria which may have been ingested with food.
2.
Some food types begin to be chemically digested in the stomach. Food digestion requires
biological catalysts called enzymes Low pH levels in the stomach
will activate enzymes that help breakdown proteins. So the release
of acid by the stomach helps in the chemical digestion of some foods.
•
Why doesn’t the stomach acid attack the wall of the stomach?
The stomach walls are coated with a layer of mucous.
The mucous is not broken down by HCl (unlike the cells in the
epithelial (inner lining) of the stomach.
•
However, the stomach may produce EXCESS ACID under certain conditions
(e.g. excess alcohol, excess ingestion of certain foods, smoking, stress and some anti-inflammatory
drugs (like aspirin)). This may cause these conditions:
1.
acid indigestion - discomfort
2.
heartburn - aka acid reflux - the acidic stomach contents move back up into the
esophagus
3.
ulcers – extensive damage to the stomach wall
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Chemistry 12 (SL + HL)
Unit 6 / IB Topic D2
ANTACIDS – NEUTRALIZING EXCESS STOMACH ACID
•
Antacids are medicines used to neutralize the excess acid that the stomach may
produce.
•
Antacids are essentially weak inorganic bases (metal carbonates/hydroxides and they
react with acids to form a salt and water.
•
There are several chemicals used as antacids. Write the equation for the neutralization of HCl by
these antacids:
1.
bicarbonates – e.g. sodium bicarbonate
NaHCO3 + HCl  NaCl + CO2 + H2O
2.
calcium carbonate
CaCO3 + 2 HCl  CaCl2 + CO2 + H2O
3.
aluminum hydroxide
Al(OH)3 + 3 HCl  AlCl3 + 3H2O
4.
magnesium oxide
MgO + 2 HCl  MgCl2 + H2O
5.
magnesium hydroxide
Mg(OH)2 + 2 HCl  MgCl2 + 2H2O
•
Antacids help to RELIEVE / reduce the symptoms of excess stomach acid by neutralizing it
– i.e reduced pain, discomfort and inflammation.
However, they do NOT directly repair any damage caused by excess stomach acid to the lining of
the stomach.
By neutralizing stomach acid, they do allow the wall of the stomach to mend and reduce
the effects of acid on ulcers.
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Chemistry 12 (SL + HL)
Unit 6 / IB Topic D2
ANTACIDS – Advantages and Disadvantages
type of antacid
advantage
disadvantage
magnesium salts
fast acting
(soluble salts)
aluminum salts
slow acting
(low solubility salts)
causes constipaiton
aluminum linked to development of Alzheimer’s
disease;
possible bone damage if used for long periods
of time (because they block calcium uptake)
carbonates and
bicarbonates
inexpensive
formation of CO2 gas  bloating, belching and
flatulence;
carbonates may contribute to the formation of
kidney stones;
sodium ions increase blood pressue
laxative effect  diarrhea
ANTACIDS – Additional Ingredients
Some antacids medications contain other chemicals that do not neutralize acids. These extra ingredients
do prevent or reduce the side effects of antacids, or they reduce other effects of excess stomach acid.
1.
antifoaming agents (e.g. dimethicone)
- reduce surface tension  reduce bubble size  less gas produced
2.
alginates
- float on the stomach contents and form a neutralizing layer
- prevents reflux back into the esophagus
ANTACIDS – Stoichiometry Problems
Which is the more effective antacid – 1.00 g of magnesium hydroxide or 1.00 g of aluminum hydroxide?
Calculate the number of moles of HCl neutralized by each antacid.
Mg(OH)2 + 2 HCl  MgCl2 + 2 H2O
moles Mg(OH)2 = 0.0171 mol
moles HCl neutralized = 0.0171 x 2 = 0.0342 mol
Al(OH)3 + 3 HCl  AlCl3 + 3 H2O
moles Al(OH)3 = 0.0128 mol
moles HCl neutralized = 0.0128 x 3 = 0.0385 mol
 ∴ more effective because more moles of HCl are
neutralized
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Chemistry 12 (SL + HL)
Unit 6 / IB Topic D2
QUESTIONS
1.
Are antacids acids or bases?
2.
State four types of compounds that are found in antacids and write a balanced equation for the
reaction of each one with the hydrochloric acid in stomach.
a)
b)
c)
d)
3.
Equal masses of which of the following compounds neutralizes more HCl - Mg(OH)2 or NaHCO3 ?
Explain.
4.
Why is there acid in stomach?
5.
What are the problems associated with excess stomach acid?
6.
Antacids often include alginates. Why?
7.
Antacids often include dimethicone. Why?
8.
Some antacids combine both magnesium and aluminum salts. Suggest a reason for doing this.
9.
What is a disadvantage of antacids containing carbonates or bicarbonates?
10. Which type of antacid is the fastest acting?
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