Rate of Reaction Between Calcium Carbonate and Hydrochloric Acid
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The aim is too investigate what factors affect the rate of reaction
between calcium carbonate and hydrochloric acid.
The variable I am intending to use in the experiment is Hydrochloric
Acid. I want to find out how different strengths of acid affect the
speed of the rate of reaction.
The variables that could affect the rate of reaction are:
Â· Concentration of Acid
Â· Surface Area
Â· Increase Pressure (this is not applicable in this experiment)
Â· Catalyst (this is not applicable in this experiment)
Â· Mass of Calcium Carbonate
Â· Stirring the Solution.
I will set up the experiment as shown in the diagram below. Looking at
the above variables, I have chosen to change the strength of the
Hydrochloric Acid, as there are more than five different strengths of
acid. This will let me take at least five sets of results, and if the
experiment is repeated I can take an average and create a more
I think that the higher the concentration of the acid, the faster the
reaction will occur. This relates to the collision theory and the
section of acid and concentration of it. I think the 1.75molar
hydrochloric acid is likely to be a lot faster than that of a 0.75
molar acid - the stronger the acid, the higher the likelihood of
collision, which goes onto the reaction happening faster. If there is
a higher concentration of acid, there is a higher chance of
collisions, due to more particles colliding.
I took some trial runs to help me with my experiment. The first trial
run was to find out what sort of volume of acid to use. I tried 100
ml, and found after the water in the boiling tube had been displaced
the reaction still carried on a long time afterwards. I then tried 25
ml of acid and found the reaction did not last enough for the water to
be displaced. I then used 50 ml and found this was a sufficient amount
of acid for the experiment. My second part of the test was to find out
how much calcium carbonate to use in the experiment. I tried 1g of
calcium carbonate and this took a very long time, in which I did not
have a lot of. I then tried 10g of calcium carbonate, and although the
reaction occurred fairly fast, I thought that maybe it was too fast
for me to take accurate readings. I decided to use 4g and this gave me
time to stop the stop clock and give me more accurate results but was
fast enough to get the experiment repeated twice in the allotted time.
To make this a fair test I filled a measuring beaker to exactly 50 ml
each time I repeated the experiment. This meant there could be no
difference in the time because there was a different volume of acid.
Also I measured out exactly 4g of calcium carbonate for each
experiment to keep that a fair test as well. I used 3 chips each time
to try and keep the surface area a constant size. Although these
measures were in place, this could not ensure the experiment was a
completely fair test.
I first need to set up the experiment as shown in the diagram. My
first reading would be 0.75 Molar Hydrochloric Acid. I filled the
beaker with 50ml of acid. The acid was kept at room temperature of
23ËšC. I then took large marble chips, and weighed them to make it
exactly 4g of chips. I then put the chips into the acid, took the bung
and blocked the beaker. The other end of the tube was under the
beehive shell with the full boiling tube over the time. I started the
stop clock as soon as the chips were added to the acid. I then waited
until all of the water had been displaced from the boiling tube and it
was left filled with oxygen, and stopped the stop clock. I recorded
the time and then repeated the experiment. I did this for each
strength of Molar acid, 0.75, 1, 1.25, 1.5, and 1.75. This experiment
will not be a fair test for several reasons:
Â· Marble Chips: Every time I measure 4g of marble chips for each
experiment, even though I used four chips each time, there will still
be a different surface area. This means that the reaction could have
been speeded up or slowed down depending on the surface area. Also
when repeating the same experiment again it was impossible to use the
original chips again making not the exact same surface area.
Â· Acid: In each experiment I could not use the same acid. This is
because the original acid had been neutralised, so I needed to get
50ml of new acid for each experiment. This could be classed as not
being a fair test because I was not using the same acid when I
repeated the experiment.
The speed of a reaction depends upon how often or how hard particles
collide. Particles have to collide to react with each other. Here are
the different factors that could affect the collision theory and the
rate of reaction.
1. Concentration - This increases the likelihood of making more
collisions. This is because more particles are likely to collide. This
is one of the points which relates to this experiment.
2. Increase the temperature - The particles will be given more energy
and will move around more quickly there increasing the likelihood of
collisions. The temperature of the acid will be kept the same at
3. Increase the pressure - Smaller volume in which to move around,
therefore greater opportunity for collisions. The beaker will be kept
the same size so that the volume is the kept the same.
4. Surface area - Breaking a solid up increases the surface area.
Increasing the surface area increases the surface on which the
reaction can take place, therefore increasing the rate of reaction.
There will be three chips for each experiment. They are large chips
and will not be broken up. They should be the as closer size as
possible to get the same amount of surface area.
5. Catalyst - this increases the number of collisions. A catalyst is
not part of the reaction and does not change. This is not applicable
in this experiment as a catalyst is not going to be used.
Factors involved in the experiment
Here I am going to explain the factors involved in the experiment and
what will happen to them e.g. stay that same, change etc.
Â· Volume of Acid - this is going to stay constant at 50ml. I am not
going to change how much acid is in each experiment, as that would
make it an unfair test. I am however going to change the acid in
between experiments as the acid is neutralised by the Calcium
Â· Acid Strength - this is what I am trying to test in the experiment
to find out how the strength of the acid affects the rate of reaction.
For each experiment, I will be using a different strength of acid.
This is the variable in the experiment.
Â· Temperature of Acid - this is going to stay the same, it is going to
be room temperature (23Ëš)
Â· Amount of Calcium Carbonate - this is going to stay the same weight
throughout each experiment. I will be using chips labelled "large
marble chips" This will be 4g.
Â· Surface area of Calcium Carbonate - the problem I will have is each
time the surface area is likely to be different on each experiment as
each chip is not identical in size, and this is likely to affect the
rate of reaction, according to the collision theory (point 4).
The science behind the reaction
The speed of the reaction depends upon how often or how hard particles
collide. The higher the concentration of the hydrochloric acid is, the
higher the chance of the bonds breaking. This is because the stronger
the hydrochloric acid is, the more energy the molecules have so they
travel with more force which means the bonds break. If the molecules
do not have much energy they will just bounce off the bonds and will
not break. The energy is needed to break the bonds and get the
reaction started. Rates of reaction can be changed not only by
catalysts but also by changes in temperature and by changes in
concentrations. Increasing the concentration can also increase the
reaction rate by increasing the rate of molecular collisions.
"The higher the concentration the more particles collide."
The chemical reaction that occurs within this experiment is shown
HCl + calcium carbonate [IMAGE] calcium chloride + carbon dioxide +
HCl + CaCO3 [IMAGE] CaCl2 + CO2 + H2O
Results & Analysis
Here are the results for the experiment that I did. Test 1 shows the
results of my first experiment I did. The table labelled Test 2 shows
the results I took when I repeated the experiment. From these two
tables, I took an average reading and put it into a third table titled
Graph of Results
I think my results are accurate. I used exactly 50 ml of each type of
acid in the experiment, and used exactly 4 g of large marble chips
each time. The same beaker was used for each experiment after it had
been washed out and dried. This meant that there was the same amount
of space for particle collisions to occur. This was because of another
part of the collision theory:
Pressure - The smaller volume in which particles to move around, give
a greater opportunity for collisions.
This is why I used the same beaker for each experiment, so that their
was an equal chance of particles colliding in the same volume each
The graph shows the results from the average table. From the graph and
the tables I can see when the strength of the acid increases, the time
for the tube to empty decreases. This means that when a higher molar
acid is used, the reaction occurs quicker. This confirms the collision
Concentration - This increases the likelihood of making more
collisions. This is because more particles are likely to collide.
The Collision Theory in More Detail
If you have a situation involving two particles they can only react
together if they come into contact with each other. They first have to
collide, and then they may react. It isn't enough for the two
particles to collide - they have to collide the right way around, and
they have to collide with enough energy for bonds to break.
Even if the particles are orientated (in the right direction)
correctly, you still won't get a reaction unless the particles collide
with a certain minimum energy called the activation energy of the
reaction. Activation energy is the minimum energy required before a
reaction can occur
If the particles collide with less energy than the activation energy,
nothing important happens, they bounce apart. Think of the activation
energy as a barrier to the reaction. Only those collisions which have
energies equal or greater than the activation energy result in a
reaction. Any chemical reaction results in the breaking of some bonds
(needing energy) and the making of new ones (releasing energy).
Obviously some bonds have to be broken before new ones can be made.
Activation energy is involved in breaking some of the original bonds.
Where collisions are relatively gentle, there isn't enough energy
available to start the bond-breaking process, and so the particles
In order for any reaction to happen, those particles must first
collide. This is true whether both particles are in solution, or
whether one is in solution and the other a solid. If the concentration
is higher, the chances of collision are greater.
This diagram shows the effect of concentration in a liquid. There are
two reactants in this diagram. On the left side it shows there is low
concentrations of each type of reactant, therefore only a low chance
of collision. On the right hand side it shows both reactants (only one
really needs to be increased) have been increased (more concentrated)
and there is now a lot higher chance of collisions.
This diagram shows the effect of concentration with a liquid and a
solid. The red particles are the liquid and the blue particles are the
solid. On the left hand side, there is a fairly low concentration of
the liquid there for a low collision rate. On the right had side a
higher concentration of liquid has been used and a higher rate of
collisions has occurred. Both sides have kept the same mass of solid.
How this relates to this experiment
This experiment relates to the liquid and solid diagram. The lower
strengths of acid e.g. 0.75 molar used with 4g of marble chips
produces a fairly low collision rate taking longer for the reaction to
take place and the water to be displaced from the boiling tube. When a
higher concentration of acid is used e.g. 1.75 molar, there is a much
higher collision rate because of there being more particles in the
Comparing to my prediction
My prediction matched the science behind the experiment and the
results gathered from the experiment. As the concentration of acid
increased, the higher the rate of collisions and the faster the
reaction took place. My prediction was made upon previous scientific
knowledge, and trial runs of the experiment.
I think the experiment went well, apart from a few aspects which may
have affected how accurate the experiment went. Below were the main
problems encountered while doing the experiment?
Â· The replacement of the bung and the marble chips going into the acid
- This played a large part in making any of the results inaccurate. It
was very hard for each chip to go into the acid at exactly the same
time. As soon as a piece of calcium carbonate touches the acid, the
reaction starts, but if the bung was not replaced in time a small
amount of gas could have been let out of the beaker. This meant not
all the gas went through the tube into the boiling tube and the
results were not exactly correct.
Â· Temperature of the acid - This was not the variable and I was going
to test it at room temperature (23ËšC). This was very hard to keep
exactly the same for every single test as the temperature of the room
increased & decreased and it was possible that the temperature of the
acid may have fluctuated slightly, effecting the rate of the reaction
(due the temperature point of the collision theory)
Â· The stopwatch being started - This was hard to time exactly, as the
clock had to be started when the calcium carbonate touched the acid
and stopped as soon as the water level went under the rim of the
boiling tube. Because of the time between the replacing the bung and
switching on the clock it was possible that tenths of a second was
lost in the results.
Â· The surface area of the marble chips - although I managed to keep
the weight exactly 4g, I was not able to completely control the size
of the surface area. I tried to keep it as accurate as possible by
using 3 chips, as closely sized as possible. This still meant that it
was likely to surface area was not identical every single experiment.
This could make the results slightly incorrect as a larger surface
area meant more chances of collisions and would speed the reaction up.
I think the graph shows an inconsistency at the result circled at 1.25
molar. From the line of best fit, I think it should be a straight line
and although the line does not go through every single point, they all
lie very close to the line. The circled result is the exception to
this. Below is a copy of the table "Test 2", and highlighted is the
result which I think is out of place.
Comparing the results on Test 1 and Test 2, this result shows an
inconsistency to the rest. All of the other results are within 25
seconds comparatively apart from this one which has a gap of over 40
seconds. This result affected the average for the 1.25molar
hydrochloric acid and this is why it is slightly out of the place
compared to the other results. It is unclear what the problem was with
this reading, but it is more than likely to be one of the problems
stated above, perhaps more gas escaped during the first couple of
seconds of the experiment than any of the other readings, it was
possible that the stopwatch was started a few seconds after the
reaction had started or the marble chips may have had a significant
difference in surface area (the surface area being small) than the
others tested, decreasing the rate of collisions.
I think that the time taken to replace the bung on the flask is the
main aspect which limits the overall accuracy of this experiment. It
is extremely hard to put the bung in the flask before the reaction
between the hydrochloric acid and the calcium carbonate occurs. I
think this is part of the experiment which is least accurate.
To improve the accuracy of measuring of these results, I would have
monitored the experiment a lot more closely, stopping the stop watch
at the exact moment the last bit of water had been displaced from the
boiling tube. I would do this because it would give me a more accurate
time for each test. I would have liked to use some kind of technology
that would have enabled me to control the surface area and the weight
of the chips, so that I could match them both very closely, or if that
was not available, use identical marble chips (same size, same surface
area). This is because the surface area affects the rate of reaction
and therefore if the surface was identical the rate of reaction would
not be affected as much by the difference in surface area. I would
have also liked to have used a water bath set at 23ËšC giving me a
constant temperature at the same level. This would have meant the
results would have been more accurate because the temperature of the
acid would be identical in each reading.
I could have also done the experiment a different way. It could have
been done by conducting the experiment in an open flask on a balance
(scales). As the carbon dioxide escapes to the air, the mass of the
flask will decrease. I could take a reading from the balance every 30
seconds, and then plot a graph of loss of mass against time. The
gradient of the plot (the steepness of the slope) shows the rate of
the reaction (how fast it is going).
If I had more time I would have done two more things too the
Â· Increased the amount of readings per test. For example I could have
tried to get 0.25molar, 0.5molar & 2molar hydrochloric acid and test
them as well as the five I have already tested. This would extend the
line of my graph and I could have taken a better trend line. I would
have 8 different strengths of acid instead of 5 and would have more
results to plot onto my graph.
Â· I would have tried to repeat the experiment three of more times. The
reason for this is I would have at least three sets of results for
each concentration of acid, and I could then take a more accurate
average. The more results for each concentration of acid I have, the
more accurate the resultant average is. I could then plot the average
data onto a graph and this would've given me a more detailed trend
line, and confirmed my thoughts of it being a straight line.
If I had incorporated both of these points into my experiment (time
allowing) I feel as though my graph could be very accurate, showing a
more detailed trend line which I would have felt showed the results a
lot more clearly and I think this would stand as better evidence than
my current graph and average results table.