Antacid Tables
How effective is that antacid tablet?
We are going to use a technique called titration to
find out how effective the tabs are.
There are 4 stations. Each station has one type of
antacid. You will divide yourselves in to 4 groups
and each group will do the titration
Set up
Each group will record their observations.
You need to get a complete set of data from all 4
stations for your practical.
Record you results on a table
Brand
Volume HCL
Used (ml)
50
50
50
50
Volume NaOH
used (ml)
Vl of HCL
Absorbed (ml)
Titration
An operation, used in volumetric analysis, in
which a measured amount of one solution is
added to a known quantity of another solution until
the reaction between the two is complete. If the
concentration of one solution is known, that of the
other can be calculated
Step 1
Add exactly 50 ml of HCL (stomach acid) to a
flask
Crush 4 tabs of antacid and add them to the
solution of HCL in the flask
Swirl the flask and completely dissolve the tabs in
the solution
Step 3 – Titration set-up
One Buret has HCL
Read off the top of the Buret how much
is in it in ml.
Turn the tap and drain off 50ml
Step – 1: The reactions
Compound
Chemical Formula
Chemical Reaction
Aluminium 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)
Calcium Carbonate is the most common compound you will
find in antacid tabs
Step 2
Add 5 drops of phenolphthalein to the flask.
This is an indicator that will turn pink in the
presence of a base
Titration
You are going to add NaOH solution to the HCL in
the flask. NaOH is a base. You are going to react
a base with an acid.
NaOH + HCl → NaCl + H2O?
Once all the HCL has been reacted with the
NaOH the mixture will turn pink.
Video 1 Video 2
Step 3 Titration set-up
The other Buret has NaOH.
Record from the top of the buret how
much is in the Buret.
Open the tap and drain off the NaOH.
Swirl the flask around and mix the
reactants.
After a while the mix will turn pink
as you saw in the video.
If you stop filling and it starts to turn
milky add a little more NaOH until it
stays a nice light pink.
Read off from the bottom of the buret
And calculate how much you have used.
Summary
So we mixed up about 50 ml of HCL with some
crushed up antacid.
We did this to simulate what happens when you
take an antacid to neutralise stomach acid.
The question is, how effective is the ant acid?
Quick-eze
Lets consider the reaction with good old quick-eze.
One tab contains the following
Calcium Carbonate – 780mg
Magnesium Carbonate – 130mg
Sodium Trisilicate – 130mg
The major chemical is Calcium Carbonate
Calcium carbonate - CaCO3(s) + 2 HCL(aq) -----> CaCl2(aq) + H2O(l) + CO2(g)
The other chemicals are used to deal with side effects like constipation and diarrhea
Conservation of mass
We had 50ml of HCL. We mixed an amount of
antacid tab. The antacid tab reacted with the HCL
and the product of this reaction was water and
carbon dioxide gas.
Was all the HCL changed in to water and CO2?
If there was HCL left over. If we know how much
is left over we can calculate how much was
absorbed!
Restate the problem
Effectiveness of antacid
HCL + Tab
Tab reacts with HCL
Some HCL is left over
We know how much HCL we started out with
HCL start – HCL let over = How much absorbed
50ml – 10ml = 40ml absorbed
To do this we need to find out much HCL is left
Conservation of Mass
You cannot get more out of the reaction that you
put in. Only so many CaCO3 molecules were
available to react with HCL.
If there are less molecules of CaCO3 than HCL
you get HCL molecules left over.
Simple. So how much is left over?
The first reaction
(Calcium carbonate) CaCO3(s) + 2 HCL(aq) -----> CaCl2(aq) + CO2(g) + H2O(l)
Left over HCL
HCL
Quick eze
+
50ml of
HCL
Co2
H20
CaCl2
Reactants
Products
Q – How much HCL is left?
Second reaction – The Titration
0 ml
NaOH
-10 ml
Pour in an amount
of NaOH base to
React with the HCL
NaOH
The remaining HCL reacts with the
NaOH and the products water
and salt. The chemicals in the flask
turn light pink. When this happens
we know that all the HCL has been
used
H20 &
NaCL
HCL
HCL
Co2
Co2
Co2
H2O
CaCl2
H20
H2O
CaCl2
CaCl2
Summary
Lets say we measured out 10ml of NaOH to turn the
remaining HCL to water and salt.
So there must have been 10ml of HCL left in the flask
that had not been converted by the antacid!
We started with say 50ml. There was 10ml left over
The tab reacted 40ml of HCL acid
Boom Boom!!
Almost There!
Basic
Acidic
When the flask turned pink we had just enough NaOH to mix with the remaining HCL
At that point the PH was neither acid or base but almost neutral. If you put in to much
NaOH the flask turned a deep pink! You had more base than acid.
Conclusion
We looked at three different antacid tabs.
The entire point of the experiment was to compare
how much HCL the antacid tabs neutralised. To
find that out we used the titration reaction and
added NaOH to find out how much HCL was left
Once we know that we can calculate how much
was absorbed by the Tabs
Conclusion
We mix say 50ml of HCL with a Tab
We used Titration to find out how much HCL was left over
We subtract the amount of HCL we started with from how
much HCL was left over
We know how much HCL was absorbed
We compare the results for each group and see if the
different Tab absorbed different amounts of HCL
This tells us how effective each Tab type was
Simulated Results
Brand
Volume HCL
Used (ml)
Volume NaOH
used (ml)
Vl of HCL
Absorbed (ml)
Quick eze
50
10
40
Milanta
50
18
32
Tums
50
5
45
Gaviscon
50
17
33
If you don't have a complete set of results, use these