COMPARATIVE STUDY OF SOME COMMERCIAL ANTACIDS
INTRODUCTION:
Gastric acid is a
digestive fluid, formed in the stomach. It has a pH of 1.5 to 3.5 and is composed of hydrochloric acid (HCl) (around 0.5%, or 5000 parts per million)
as high as 0.1 M, and large quantities of potassium chloride (KCl) and sodium chloride (NaCl). The acid plays a key role in digestion of proteins, by
activating digestive enzymes,
and making ingested proteins unravel so that digestive enzymes break down the
long chains of amino acids.
Gastric acid is produced by cells lining the stomach, which
are coupled to systems to increase acid production when needed. Other cells in
the stomach produce bicarbonate, a base,
to buffer the fluid, ensuring
that it does not become too acidic. These cells also produce mucus, which forms a viscous physical barrier to prevent gastric
acid from damaging the stomach. Cells in the beginning of the small intestine,
or duodenum, further
produce large amounts of bicarbonate to completely neutralize any gastric acid
that passes further down into the digestive tract.
The presence of gastric acid in the stomach and its
function in digestion was first characterized by United States Army surgeon William Beaumont around 1830. Beaumont was able to study the stomach action
of fur trapper Alexis St. Martin due to the latter's gastric fistula.
Gastric acid is produced by parietal cells (also called oxyntic cells) in the
stomach. Its secretion is a complex and relatively energetically expensive
process. Parietal cells contain an extensive secretory network (called canaliculi) from which the gastric acid is secreted
into the lumen of the stomach.
These cells are part of epithelial fundic glands in the gastric mucosa. The pH of gastric acid is 1.35 to 3.5 in the human stomach lumen, the
acidity being maintained by the proton pump H+/K+ ATPase. The parietal cell releases bicarbonate into the
blood stream in the process, which causes a temporary rise of pH in the blood,
known as alkaline tide.
The resulting highly acidic environment in the stomach
lumen causes proteins from food to
lose their characteristic folded structure (or denature). This exposes the protein's peptide bonds. The chief cells of the
stomach secrete enzymes for protein breakdown (inactive pepsinogen and rennin). Hydrochloric acid activates pepsinogen into the enzyme pepsin, which then helps
digestion by breaking the bonds linking amino acids, a
process known as proteolysis. In
addition, many microorganisms have their growth inhibited by such an acidic environment,
which is helpful to prevent infection.
.
Antacids are bases used to
neutralize the acid that causes heartburn. Despite the many commercial brand,
almost all antacids act on excess stomach acid by neutralizing it with weak
bases. The most common of these bases are hydroxides, carbonates, or bicarbonates.
The following table contains a list of the active ingredients found in several
common commercial antacids, and the reactions by which these antacids
neutralize the HCl in stomach acid.
|
Compound
|
Chemical Formula
|
Chemical Reaction
|
|
Aluminum hydroxide
|
Al(OH)3
|
Al(OH)3(s) + 3 HCl(aq)
-----> AlCl3(aq) + 3 H2O(l)
|
|
Calcium carbonate
|
CaCO3
|
CaCO3(s) + 2 HCl(aq)
-----> CaCl2(aq) + H2O(l) + CO2(g)
|
|
Magnesium carbonate
|
MgCO3
|
MgCO3(s) + 2 HCl(aq)
-----> MgCl2(aq) + H2O(l) + CO2(g)
|
|
Magnesium hydroxide
|
Mg(OH)2
|
Mg(OH)2(s) + 2 HCl(aq)
-----> MgCl2(aq) + 2 H2O(l)
|
|
Sodium bicarbonate
|
NaHCO3
|
NaHCO3(aq) + HCl(aq)
-----> NaCl(aq) + H2O(l) + CO2(g)
|
AIM OF THE EXPERIMENT:
In this experiment, several brands of antacids will be analyzed to
determine the number of moles of acid neutralized per tablet and the cost
analysis of each tablet. The analytical procedure used is known as back
titration. In this procedure, a known amount of HCl, which is in excess,
will be reacted with a weighed portion of a ground antacid tablet. The HCl remaining
after the antacid neutralization reaction occurs will be determined by
titration with a standardized NaOH solution to a phenolphthalein endpoint. The
number of moles of HCl neutralized by the antacid (HClneutralized)
is the difference between the moles of HCl initially present in the excess (HClinitial)
and the moles of HCl titrated by the NaOH (HCltitrated).
HClinitial – HCltitrated = HClneutralized
No comments:
Post a Comment