EXPERIMENTAL: AN INVESTIGATION INTO THE EFFECT OF TEMPERATURE ON THE 
SPEED AT WHICH A BRAND OF INDIGESTION TABLETS DISSOLVES IN AQUEOUS 
HYDROCHLORIC ACID

Introduction
Digestion is the name given to the series of physical and chemical
processes by which complex insoluble foods are hydrolyzed to simple 
soluble substances that can be absorbed into the bloodstream.  Dilute
hydrochloric acid provides the acidic conditions necessary for stomach
enzymes to continue the digestive process that starts in the mouth;
however, an excess of stomach acid results in 'indigestion'.  Tablets 
containing a base - such as aluminium hydroxide, calcium carbonate, 
magnesium hydroxide, or sodium hydrogencarbonate - are available which 
relieve indigestion by partially neutralizing the excess acid; e.g.,
      2HCl(aq) + CaCO3(s) ——————————® CaCl2(aq) + H2O(l) + CO2(g)
The homeostatic temperature of the stomach is roughly 37°C.  However, 
significant variations from this temperature will inevitably result 
from ingesting liquids and foods, and such variations might reasonably 
be expected to affect the physical and chemical processes of digestion.

In this investigation, you are required to examine the hypothesis
that: Within the range ________°C, the speed (S) of dissolving of
brand ____________ indigestion tablets in aqueous hydrochloric acid  
(2.00 mol dm-³) is in linear proportion to the temperature (T) of
the acid; i.e., S = k × T + c'.

Method
1.  Collect a _____°C thermometer, and measure room temperature; then
compare this value with that obtained using an accurate reference
thermometer.
2.  Using the available insulating material, make a jacket that will
fit a small glass beaker.
3.  Using a measuring cylinder, or a bulb-pipette equipped with a
safety-filler, or a burette, place 25.0 cm³ of dilute hydrochloric acid
(2.00 mol dm-³) into a scrupulously clean beaker.
4.  Place the beaker into the 'home-made' insulating jacket.
5.  Measure the temperature of the acid; then, simultaneously, add one 
tablet to the acid and start the clock.
6.  Stop the clock when the tablet has completely dissolved; and then
immediately record the temperature again.
7.  Repeat steps 3 to 6, but each time change the temperature of the
acid (within the range _____°C), using either an ice-bath or a heat
source.
8.  Finally, after carefully examining your raw data for any anomalous
results, carry out appropriate duplicate experiments.

Notes
1.  Both the insulating jacket and the outside of the beaker must be
absolutely dry for each experiment.

2.  For the present investigation, you will need to use this equation:
speed (in ms-¹) = 1000 ÷ time (in s).

3.  Your write-up should include, in addition to a complete summary of
your results and conclusions presented in the most suitable form, a
critical evaluation of your investigation.

4.  The rates of chemical reactions are affected by several independent
variables, including both the concentration and surface area of the 
reactants.  So, show on the graph paper, using appropriately labelled 
sketch lines, how you would expect the speed of reaction to change by: 
(a) using more dilute hydrochloric acid; and (b) crushing the tablets.

Dr. R. Peters                  Next                      Contents' List