The preliminary work I have carried out has helped me decide on some factors I
will use in my experiment: A study to show which factors affect the rate of
reaction between calcium carbonate and hydrochloric acid.
The concentration I have decided to use is 1mol. This is because if I had
made the solution any more concentrated than this there would have not been
enough time to record results accurately. The amount of acid will be 50 (cm3).
Also I have decided to use medium sized marble chips because the small ones
reacted to quickly so there was not enough time to record results and the big
one’s took too long to react where as the medium sized chips gave an accurate
reading but also reacted at a reasonable pace.
Finally, I have decided to use 10 seconds as the amount of time before I
begin timing each result. This will give a clear path of the reaction.
Experimental procedure
Apparatus:
• 2x retort stands
• 2x boss and clamp
• conical flask
• marble chips (medium sized)
• hydrochloric acid (1mol.)
• delivery tube
• trough
• measuring cylinder
• funnel
• stop clock
• goggles
• Bunsen
• Gauze
• Heat proof mat
Diagram:
Method:
Firstly, to make sure the experiment is a fair one I would have to:
• Make up one batch of acid so I am using the exact same one for every
experiment.
• Also I must wash off any excess dust off the marble chips. You must do this
because it would affect the mass of the marble chip and the surface area of it.
• Make sure that none of the marbles or dust get stuck around the edges of the
conical flask or in the funnel as this would give you inaccurate readings
• You must also decide whether you are going to start the stop watch as you are
putting the marble chips in or after you have put them in. It does not matter
which one as long as you keep it accurate throughout.
• Do repeats of all your experiments to make sure they have been accurate and so
you can cross check results.
I would then weigh out 5g of medium sized marble chips and a beaker of 50 cm3 of
hydrochloric acid (1mol.). I would then set out the apparatus as shown in the
diagram and fill the measuring cylinder completely with water making sure no air
bubbles got in. You could cover the end with your hand and tip it upside down in
the trough so when you release it under the water no air will be able to get in.
I would then add the 50 cm3 of acid followed by the marble chips. Filter
the marble chips into the conical flask making sure none have got stuck round
the edges. I would then start the stop clock as soon as I had replaced the bung
of the delivery tube back into the conical flask.
As it’s reacting the water from the tub will be pushed out by the gas
collected. You must record your results at each 20 cm on the measuring cylinder
which are marked at one side.
The experiment above was for acid at room temperature. After you have
completed that experiment you can then heat the acid on the Bunsen (as shown in
the diagram) to the temperature you need to record the results for. In my case
it will be 30 degrees.
Results table:
Temperature = ? Degrees
(Cm3) Volume Time (sec's) Repeat 1 Repeat 2 Average
20
40
60
80
100
120
140
160
180
200
This should be recorded at every temperature and should be repeated twice for
accuracy. Also you will then be able to average the results for each
temperature.
Graph:
For each set of results a graph should be plotted and a line of best fit should
be used on each temperature.
Safety:
1. Wear safety goggles at all times
2. Keep acid away from skin and clothing
3. make a clear work space
4. never leave your experiment unattended
5. tie hair back
6. Light Bunsen on blue flame
Analysis
Trends:
• In all experiments as the temperature went up the rate of reaction increased.
• As the temperature went up so did the amount of collisions
• As the amount of collisions went up so did the amount of successful ones.
• As the temperature went up the quicker it reached activation energy.
• Time is directly proportional to the volume.
Conclusion
The quicker the temperature went up the more speedily the reaction occurred.
Sometimes in the results and graphs I received slightly odd results that did not
fit in with the rest of the pattern. This would have been because some of the
constants, e.g. dust on marble chips, may have altered slightly. Also not every
collision was successful because sometimes the activation energy may not have
been reached and the particles will therefore just bounce off each other.
Comparison with prediction
The conclusion above supported my prediction because as the temperature went up
the rate of reaction increased.
There was a few inaccurate results because I did my experiment
systematically thus ruling out human error but because of chemical imbalances,
e.g. sudden rushes of air bubbles, the results weren’t always fair.
Scientific knowledge
Using my scientific knowledge from the previous experiment I can determine why
some observations, measurements or data could have been inaccurate:
• The molecules when left at room temperature may not have reached activation
energy thus giving less successful collisions.
• Sometimes when the particles collided they may not have reacted but instead
just bounced off each other making the reaction slower.
• Some air may have been trapped in the top of the cylinder before the
experiment had commenced causing all results to be inaccurate.
• The bung in the delivery tube which fits into the conical flask may have been
leaking. This apparatus error could cause some gas to have leaked out giving
again inaccurate results.
• When the marble chips were placed in the acid the reaction would have began
before the delivery tube bung was replaced meaning that some off the gas given
off would have been wasted giving unfair results.
Evaluation
Some of the results I got did not fit in with the rest or follow the same
pattern. These factors can cause problems in getting accurate answers which
could explain the anomalous points:
• Room temperature can be a problem as it can fluctuate from hot to cold whilst
you are carrying out an experiment or if you have to continue the experiment on
a different day the room may be hotter or colder from the day you started
getting the results making them less accurate.
• The marble chips are not all the same size so their surface area will be
different and also the dust collected on them may alter their mass. Even if we
did wash the dust of the fact that the marble chips will be now wet will change
their mass also.
• The acid concentration can be kept quite accurate but if you make up some more
it won’t have the exact same concentration as the other. This will also decrease
the accuracy of your results.
Evidence
The evidence in my results does support my prediction because as the temperature
went up the rate of reaction increased. Also I said this would only happen when
we kept everything constant which was true because we only got an anomalous
result when one of the problems from the above list occurred causing some of the
supposed constants to vary.
Improvements
Some improvements could be made to the methods I used:
• Instead of making up more acid every time I needed it I could have made up a
lot of it at the start and used it as I went along so that the concentration of
it was exactly the same throughout the experiment.
• When I was heating the acid to a certain temperature I would have to place the
conical flask over the Bunsen so by the time I had secured it onto the clamp
again and added the marble chips it may have decreased in temperature by a few
degrees. I could correct this by adjusting the apparatus so I would not have to
remove the flask whilst heating so I could simply and speedily add the marble
chips straight away.
• When filling the measuring cylinder sometimes bubbles of air would get trapped
at the top of it o it would not have been completely full of water and would
have given it a head start. You could increase the accuracy of this by placing
card over the top of the cylinder or a square of plastic instead of your hand.
• When recording the results as the water went down it sometimes went quite fast
so when I called now for my partner to record results she may have been a few
split seconds out and I may not have called when it was at the exact right
volume. This could be improved with a clearer marked cylinder.
• When I removed the dust off the marble chips by washing them some were wetter
than others which would have changed their mass. I could have improved this by
drying them all equally.
• The marble chips which I used, although all medium sized, were all different
shapes which would have affected the surface area. This could have been improved
by picking ones of similar shape and size.
• Also the room temperature experiment was effect as when I did the first result
and first repeat it was warmer in the room than when I did the second repeat the
next day. This could be improved if I could have had more time to complete the
experiment.
Further work
Further investigating of the factor which affects the rate of reaction of marble
chips and hydrochloric acid could be concentration. If we had kept temperature
and all other factors constant except concentration we would have been able to
see what effects it would have had to the rate of the reaction.
You could use the exact same apparatus as in the previous experiment for
temperature except you would not need a Bunsen but you would need about five
different concentrations. They would need to go up by 0.2 each time so you could
see a clear difference in results and follow the path of them easily.
Also I could make a prediction using my knowledge from the previous
experiment on temperature that the more concentrated the solution became the
quicker the rate of reaction. This is because the more concentrated the solution
is the more particles it will contain and the more particles it contains will
give a higher chance of them colliding. This will result in more successful
collisions which would speed up the reaction.
