An Investigation to see How the Concentration of Hydrochloric acid
affects the Rate of Reaction with Calcium Carbonate
I am going to investigate how concentration of hydrochloric acid
affects the rate of reaction between hydrochloric acid and indigestion
tablets which contain mainly calcium carbonate.
From my background knowledge from class work and books, (see
references) I have found out that if you increase the concentration of
, the rate of reaction
will increase and the time of
the reaction will decrease. The concentration is dependant on the
proportions of hydrochloric acid and water in the solution. The
stronger the hydrochloric acid is, the higher the concentration is.
I know from my research that other things can affect the rate of
reaction, for example:
Temperature of acid- the higher the temperature of the acid is, the
more energy the particles have to move around, therefore there are
more collisions and so a faster rate of reaction. There is a certain
amount of energy needed for the particles to react which is called the
activation energy, so when the temperature of the solution is higher,
it gives more particles sufficient energy so they move faster to react
when they collide more.
Size of the particles- when the reactant is a solid then it can be
broken down into smaller pieces or into a powder giving it different
surface areas. The smaller the pieces, the bigger the surface area is
and therefore there is more area for the acid to react with it, and so
there is more chance of the particles colliding, so the rate of
reaction will increase.
Catalysts- this weakens the bonds in the reacting molecules so it
seems to lower the activation energy for the reaction. This means that
there can be many more successful collisions because particles will
have more energy than the activation energy, and so the reaction will
In order to keep my experiment fair, I must keep all the variables the
same except concentration, which is what I am investigating.
From my preliminarty experiments, I have found that a gas is let off
in this reaction and having testing by putting it with lime water, I
have concluded that the gas is carbon dioxide because the lime water
The equation is:
+ Hydrochloric acid Calcium Chloride + water
+ carbon dioxide
To find the rate of reaction, I will measure how long it takes to
produce a certain amount of gas. To work out the rate of reaction, I
have to divide the amount of gas I will collect with the time.
Rate= amount of gas collected/ time
In order to make this experiment fair, I will keep all the variables
the same, except concentration. I will keep the mass of calcium
carbonate the same by using one tablet each time. The masses of each
tablet vary, but only by a tenth of a gram either side of 1.01g, which
I think is not a large enough difference in mass to make a difference
to my experiment. I will try to do all my experiments on the same day,
so the room temperature will be the same, which means the temperature
of the acid will not change. I will use a burette to measure the
amount of hydrochloric acid and water, so the volume of acid will be
the same. I will keep the surface area the same because I will use the
whole tablet and so each one will have the same surface area because
they are all similar in size. Finally, I will use the same apparatus
throughout my whole experiment to make it a fair test.
I have done preliminary experiments in order to find the amounts I
should use for the variables. I chose to collect 40cm³ of gas, 50cm³
of acid solution and use half a intigestion tablet and crush it. I
found three problems with using this half a crushed tablet. The first
problem was the fact that it did not react very strongly, and it did
not collect more than 24cm³ of gas with my lowest concentration of
acid, secondly it was difficult to get exactly half a tablet, and this
would take too long in my real experiment if I was to get exactly half
a tablet each time. Lastly, I did not know when to start my stop
clock, because the time delay from the first bits of calcium carbonate
falling into the acid, to the last bits of calcium carbonate falling
was quite long and in between this, some gas was lost. This has made
me decide to use a whole intigestion tablet, so I do not loose as much
gas inbetween putting the tablet into the solution and putting the
bung on the conical flask.
I decided that the lowest concentration I will use is 1M of
hydrochloric acid., which took 85 seconds to collect 40cm³ of gas.
This highest concentration I will use is 3.8M of hydrochloric acid,
which took 50 seconds to collect 40cm³.
From my preliminary experiments I have decided to:
Use one whole tablet, 50cm³ of different acid concentrations and time
how long it takes to collect 40cm³ of carbon dioxide gas.
My prediction is:
The higher the concentration of hydrochloric acid, the quicker the
reaction time is with the indigestion tablets.
This is because I have found out that the reaction will be quicker as
the concentration increases, because the higher the concentration is,
the more particles of acid there are which are closer together to
collide more with each other and therefore react with each other, and
so the reaction will be quicker. This is called the collision theory.
I will use a graph to show my results, and I know from previous
knowledge that the graph should be directly proportional, which means
as the concentration increases, so does the rate of reaction. If the
concentration is doubled, the rate of reaction is doubled, because
there is twice as much possibility for collisions because there are
twice as much particles. The line of best fit should go through the
origin because when there is no concentration of acid, there are no
particles to react. I expect to get a graph which looks like the
· 1 burette containing hydrochloric acid
· 1 burette containing water
· 1 conical flask
· bung and deliver tube
· gas syringe
· stop clock
· clamp stand
I am using burettes because they have an accuracy of 0.1cm³ which
means I can measure the volumes of water and acid very accurately, and
the range of the burette is 0-50cm³ of liquid, which is enough for
what I need. I will use a gas syring which is accurate to 1cm³ of gas
collected, and ranges from 0-100cm³ of gas which is accurate enough if
I am to collect 40cm³ of gas. The stop clock is accurate to the 100th
of a second, but I will round the time to the nearest second, because
it is more realistic when remembering human reaction times, which is
about 0.1 seconds. In order to not let any gas escape, I will make
sure I put the delivery tube and gas syring securely together.
· Set up apparatus as above
· Take 50cm³ of the following concentrations at one time, using the
burettes of acid and water-1M, 1.4M, 1.8M, 2.2M, 2.6M, 3.0M, 3.4M,
· Put the acid solution into a conical flask
· Put 1 intigestion tablet into the the acid and put the bung on.
· Start the stop clock and time until the marker reaches 40cm³.
· Do this for all the concentrations.
I will use a range of 2.8M of hydrochloric acid, the lowest
concentration is 1M and the highest is 3.8M. I decided to use these
concentrations, because in my preliminary experiments, I saw that the
reaction was too slow with a concentration below 1M, and that the
reaction would be too fast above 3.8M. I have chosen to do 8 different
concentrations, because I will not have enough time to do more, and I
will still beable to draw a concusion even if I only use 8 different
concentrations. I will have to use both 2M and 4M hydrochloric acid in
order to make the different concentrations of acid. The ones which are
2M or below I will make with the 2M hydrochloric acid, and for the
rest 4M hydrochloric acid. I will try to use as little of the 4M acid
as possible, because it is more dangerous than the 2M.
I will take as many repeat readings as I can in the time that I have,
because repeats will help me to make sure I do not get any anomalous
results. I will reapeat the anomalous results first. The more repeats
I do, the more reliable my results will be.
I will use 2M and 4M hydrochloric acid which both have IRRITANT
warnings so I will be careful using them and try not to get them on my
hands or in my eyes. I will use goggles to protect my eyes.
This conclusion supports my prediction well because my results show
that the higher the concentration, the quicker the reaction is because
there are more particles to react with each other, and so there is
more chance for them to collide and therefore the reaction is faster,
which is what I originally assumed in my prediction.
My graph shows it is directly proportional, because if I take the
concentration of 1.5M of hydrochloric acid, and find the rate of
reaction using my graph, it shows that the rate of reaction is 0.36
cm³/s, and using the graph if I double the concentration to 3M, the
rate of reaction is 0.72 cm³/s which is exactly two times faster than
the reaction with 1.5M which shows it is directly proportional.
In the following table, I have calculated the average time and rate of
reaction for all the different concentrations. I have then worked out
the difference between each rate in order to find if there is a trend
in how much quicker the reaction is which each concentration.
From this table, I can see there is a trend, because as the
concentration goes up by 0.4M each time, the rate goes up by 0.07,
0.08 or 0.09 cm³/s which are very close to each other and shows that
the rate is quite consistent because no matter what the concentration
is, the rate goes up in a certain way on average of 0.08 cm³/s.
The only results that do not go with trend are the 3.8M
concentrations. On my graph I have circled them as anomalous results.
There can be several explanations for this which I will cover in the
The following diagram is a simple way to help show why the rate of
reaction increases with the concentration:
My experiment has helped me with my conclusion that the rate of
reaction increases as the concentration of the hydrochloric acid
increases, and has given me evidence to help explain it.
My results are as realiable as I could make them using the apparatus
and the time I had. From my results I can say that most of the results
are quite reliable and accurate to what they should be because I got
the results I expected. However, I did get two results which I would
say are anomalous. I decided that these two results are anomalous
because according to my background knowledge and the rest of my
results, I knew that I should get a directly proportional line of best
fit, and the rest of the results are very near to this line of best
fit. I know that my line of best fit is correct because as the
concentration doubles, the rate doubles. The results for the 3.8M
showed that the rate was slower than the rate of reaction with a lower
concentration of 3.4M.
There are many different factors which may have affected my results.
One of the biggest faults in my experiment was the fact that I did not
have enough time to complete it in one day. Due to various problems, I
had to do the experiment on three different days. This means that all
the equipment was different which may mean that they work differently
from eachother. This makes it an unfair test. The second problem with
doing it on different days is the problem of room temperature which
can have a big effect on the rate, because as I know from back ground
knowledge, I know the warmer the acid is, the faster the reaction
because particles have more energy so there are more successful
collisions. I made the mistake of not recording which results are from
which day, so I cannot tell if this had a major effect on the results.
Whilst doing the experiment, I noticed a few problems which may also
have effected my results. First of all is the problem that I only have
two hands, so it was difficult to put the tablet in the conical flask,
close the bung and also start the stop clock, all at the same time.
When there was someone available, I asked them to start my stop clock,
but this was not possible all the time. Adding this time to human
reaction time of around 0.1 of a second, some time could have been
lost. Some gas was also lost in the time period between putting the
tablet in and putting the bung on. I tried my best to make this time
period very small, but still some gas was lost. When I had managed to
get the tablet into the acid with the bung on and time it, I noticed
that sometimes the whole tablet would not go into the acid, and so it
was not all reacting, so in order for the whole tablet, I would shake
it for a couple of seconds. I did not count how long I would do this
for each one, but when I did shake it a lot of gas would be produced,
so If I shook one flask for longer, more gas would be produced faster
because the whole tablet would be reacting with the acid and there
would be more collisions and therefore a quicker reaction.
Between each different concentration, I would wash the conical flask,
and I observed that if I washed the flask with hot water, the flask
would become hotter, or if I washed it with cold water the opposite
would happen. This meant that the temperature of the acid and water
solution would vary. This made the tests unfair because if I did some
of them with hot conical flasks and others with cold ones, the ones
with the warmer flasks would react faster because the temperature of
the acid would increase and so give the particles more energy to
If the equipment was much more sophisticated, for instance if all the
equipment would stay the same temperature or if there was special
clock which would start at the exact time the tablet touched the acid,
my results would be much more accurate, but I still found good
[IMAGE]If I could do the experiments again, I would do the following
things differently in order for my results to be more accurate. I
would make sure I did them all on the same day, use all the same
equipment, have someone to start the stopclock, have better equipment,
for instance a conical flask with a divider so the acid and calcium
carbonate won't mix until I want them to:
Apart from all of the problems, my method was suitable and the
experiment was successful because I had sufficient evidence to enable
myself to come to a conclusion which agreed with my knowledge and
prediction. I would have liked to share results with other people who
were doing the same experiment as me to see if our results were
similar, but nobody was doing the same experiment as me.
The only results which I did not think are reliable or accurate is the
reaction of the 3.8M concentration of hydrochloric acid with the
calcium carbonate, and if I had more time I would investigate this
further. I would find out why these results were anomalous because
even though I did reapeats, I still got anomalous results and so I
would like to find out why this happened. I would like to investigate
the rate of reaction with more concentrations in order to see what
happens after 3.8M acid to see if it was still directly proportional
or if the graph leveled off. Other extra investigations I would do
would include using different types of acid for instance nitric acid
or sulphuric acid and see if they changed the reaction at all. I would
also try and use different types of indigestion tablets, because the
ones I used contained ginger which I have researched about to find
that it is used for digestion, soothing aches and pains in muscles and
improves circulation problems, so I would like to investigate if this
has a different effect on the rate of the reaction or not. I put an
indigestion tablet into 1M of acid concentration and measured the
temperature before and after the reaction for one minute to see if the
reaction was exothermic or endothermic, but there was no change in
temperature, so I would like to see what effect an exothermic or
endothermic reaction would have on the experiment.
Overall I think my results are reliable because the repeats are all
very close to eachother, the biggest gap between my repeats is the
1.0M concentration which had a time difference of 6 seconds, but the
others which I had time to repeat are all around 3 seconds apart. If I
had more time I would do much more repeats to make my results more
reliable. The accuracy of my results are quite good because they are
all very close to the line of best fit. I would like to do more
experiments and repeats to make sure my line of best fit is accurate
and in the correct place. Apart from these I think my investigation