The second time the experiment took place, the mass of calcium carbonate was kept the same but changes were made on the volume of hydrochloric acid used down to twenty centimetres cubed. With these measurements it was found that it was easier to take down the times. This is a good reason to stay with these measurements because it is possible to get more accurate times as there will be less of a chance of missing a any and it can be written down to the nearest tenth of a second instead of just a second.
The third experiment the measurements were kept the same of the calcium carbonate however, there is a less concentrated acid being used. The acid used this time was only one molar. The measurements were still suitableto use as there weren't huge gaps between each time. On average the time between every ten centimetres cubed is eleven seconds. The whole of this experiment only took two minutes and forty- one seconds.
The final experiment done was with the same measurements of calcium carbonate once again but the concentration of the acid was lowered once again to a half molar. This experiment took double the time as the 1 molar therefore the experiment was only taken down to fifty centimetres cubed. Although this discards the experiment as unfair it was felt that it may not be an option to undergo this experiment for the full hundred centimetres cubed because it took too long.
Here are the results of these four experiments
As the results show the time took for carbon dioxide to be collect every ten centimetres cubed was a fairly steady time excluding the half molar.
In conclusion to this preliminary investigation we have chosen to following measurements for the main experiment:-
Volume of acid – 20 cm³
Mass of calcium carbonate – 2g
Range of concentration – 1M, 1.5M, 2M, 2.5M, 3M, 3.5M and 4M
Type of calcium carbonate – small granules as there will be a larger surface area
Temperature – room temperature (24°C which is 75°F) as this is easiest to control
Measurements – every 10cm³ starting at 10cm³ and finishing at 100cm³
It is believed that these measurements will give the best conditions possible to get accurate results.
Collision Theory
Collision theory is the activation energy which is needed for a chemical reaction to take place. Only the very fastest moving particles have enough energy to break bonds. The speed of the reaction is determined by a number of things, these are, for example:
- Concentration
- Temperature
- Surface area
- Catalyst if it’s available which in this case there isn’t one.
Concentration
The concentration can change the speed of reaction because of the amount of partials in the solution. In the diagram below there are two different concentrations. On the right there is a less concentrated solution to the right. Because of this there are now more hydrochloric acid particles in the solution to hit into the calcium chloride particles. However even though there are more particles the activation energy is the same thus meaning that if the hydrochloric acid particle doesn’t hit the calcium chloride particle with enough force nothing will happen. This is because of the bonds which need to be broken.
Temperature
This increases or decreases the speed of a reaction depending on whether the temperature is higher or lower. If the temperature is increased then the speed of the reaction will increase, on the other hand, if the temperature is lowered then the speed of the reaction will decrease. This is because when the solution is warmer the particles have more energy and so are able to move around much quicker meaning there will be more collisions. In the diagram to the right of the page you can see how there is more movement in the hydrochloric acid particles. Because of the increase in energy, as well as the speed increasing there is more of a chance that the activation energy will be reached.
Surface Area
When there is a small surface area there are always going to be particles which cannot react with anything until the particles around it have been reacted. In the diagram bellow, the first beaker has two particles which cannot be reached; this is because of the small surface area. However in the second beaker there is a larger surface area and so the two particles are able to react at the same time as the others.
Prediction
The prediction to this experiment is that the stronger the concentration of the acid the quicker the carbon dioxide will be given off. The way in which this prediction is made is by looking at the molecules of both the calcium carbonate and hydrochloric acid. As you can see in the diagrams below there are two concentrations of acid. In the first beaker there are four particles of hydrochloric acid, if the concentration of the acid is doubled there are double the amount of particles. Because there are double the quantity of particles there will be twice as many chances to for the hydrochloric acid to collide into the calcium carbonate. When hydrochloric acid particles collide with calcium carbonate particles with enough energy a reaction takes place.
Another prediction for this experiment is that the larger the surface area the faster the reaction. As you can see in this diagram with the smaller surface area which is in the first beaker, there are two particles (red) which cannot react with anything until the other particles around them have reacted. However in the second beaker the two particles are able to react with the hydrochloric acid as there is a larger surface area. So the greater the surface area is, the greater the chance is in a collision.
Fair Experiment
To keep this experiment a fair test there are a number of things which need to be done. The main ones which have to stay the same are the variables which are not going to be used to change the speed of the experiment which are the following:-
Temperature
The temperature should be kept the same all the way through the experiment as if it changes slightly it can effect the speed of the experiment. The temperature was kept at room temperature which was 20˚C which is 75˚F.
Measurements
All measurements must be done at eye level, for example when measuring 20ml hydrochloric acid; you have to go down to eye level of the 20ml mark and slowly pure in the hydrochloric acid to this volume. This has to be done on the amount of carbon dioxide being released into the measuring cylinder. If this isn’t done correctly the data isn’t going to be totally accurate.
Another thing which has to be measured right is the calcium carbonate. First the measuring boat gets put onto the chemical balance, then it is set to zero. Once it reads zero place the calcium carbonate into the boat until there is 2g in it.
Method
Apparatus list
- Conical Flask
- Bung
- Glass Tubing
- Trough
- Measuring cylinder (20cm3)
- Chemical balance
- Stop clock
- Calcium carbonates (2g of fine granules)
- 20cm³ of hydrochloric acid (1, 1.5, 2, 2.5, 3, 3.5 and 4M)
- Chemical balance
- Weighing boat
- Goggles
How to Conduct the Experiment
- Collect all of the apparatus needed for this experiment and set them up as they are in the diagram.
- Measure out at eye level 20cm³ of 1M hydrochloric acid.
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Measure out 2g of calcium carbonate using the chemical balance.
- Place the hydrochloric acid into the conical flask.
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Place the calcium carbonate and simultaneously place the bung onto the conical flask and start the stop clock.
- Times will be taken every 10cm³ of carbon dioxide collected. The times will be taken from 10cm³ to 100cm³.
- This will be repeated three times and an average will be calculated. The experiment will them be replicate using 1, 1.5, 2, 2.5, 3, 3.5 and 4 molarities.
- To ensure this experiment will be conducted fairly all of the measurements involving liquids will be measured at eye level. The experiment will also be preformed at room temperature
Evaluation
This experiment like every experiment went moderately well although there was a minority problems within this experiment. If you were to look through the results and graphs you can see that there are a handful of points are off the line of best fit. This could be down to a fault in the equipment or a hesitation from the person reading the measurements.
When conducting the experiment, I kept all the variables the same, apart from the concentration of acid, to ensure a fair test.
Problems
- The stop clock didn’t have any split seconds making the results less accurate.
- The pipe which took carbon dioxide to the measuring cylinder kept moving around and occasionally releasing itself from under the measuring cylinder.
- The clamp holding the measuring cylinder in place covered up some of the points which were needed to be seen.
- Filling the measuring cylinder with water without getting air bubbles in it.
- There are a few off points in the rate graph, this may be down to a fluctuation in temperature or the equipment may have been faulty.
Improvements to the Experiments
- there is a stop clock around in which you can simply press a button which stores that time, it is not necessary to record the time there and then as it stays on its memory, this is repeated until the end of the experiment when the results can be recorded.
- Clamp the pipe into place under the measuring cylinder to prevent it from moving around.
- Find a clap which is transparent or semi-transparent in order to be able to read all of the marks on the cylinder.
- Have a cover to stop the water from coming out of the measuring cylinder whilst inverting it, then the cover can be removed.
Looking at the graphs there is a pattern in the fact that 4M reacts twice as fast as 2M and four times faster then the 1M. This shows that as the concentration is doubled the time taken for the reaction is doubled.
If this experiment was to be repeated the way in which it would be undertaken is as follows:-
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Fill a measuring cylinder with water with NO air bubbles.
- Set up the apparatus as shown in the diagram.
- Make sure it is possible to see all of the makings on the measuring cylinder whilst setting everything up.
- Measure out finally granulated calcium carbonate to 2g using the chemical balance; make sure the balance is set to zero before placing any calcium carbonate on it. (repeat this twenty-one times)
- Measure out 20cm³ of hydrochloric acid using an accurate measuring cylinder; this must be done at eye level. (repeat this twenty-one times)Start with the least concentrated acid so that it is kept fair by not contaminating the measuring cylinder with more concentrated acids.
- Whilst performing the experiment start with the least concentrated acid to the most concentrated as it will make the experiment a fairer one.
Although this experiment was done as fairly as possible I would not rely on the results I they are not as accurate as they could have been. The stop clock was only in seconds and there was no tenths of a second on it. This shows in the rate graph as there are three off points which are quite far away from the line of best fit. This could have happened because of a fault in the apparatus. Also due to the length of the experiment it wasn’t possible to undertake the whole of it in one day. One of the days there was a fault in a piece of the equipment. There may have also been a slight change in the temperature although this would have only been by 1°C at the most.
Conclusion
In conclusion to this experiment it has been discovered that the stronger concentration has the fastest reaction time therefore saying that concentrations do affect the way in which chemicals react. Looking at 1M graph it shows that it took 131 seconds of the reaction to release 100cm³ of carbon dioxide, this is compared to the 4M graph which shows it only took 28 seconds for the same amount of carbon dioxide to be released making it over four times faster than 1M. This is also shown on the rate graph.
Looking at the graphs there is a pattern in the fact that 4M reacts twice as fast as 2M and four times faster then the 1M. This shows that as the concentration is doubled the time taken for the reaction is doubled.
In all of my graphs, the line of best fit is in the place where I believe is where it is closest to the most points and therefore being in the most accurate place.
The graphs have proved that my predictions were correct and that the more concentrated the hydrochloric acid is the faster the reaction time, the rate graph backs these up further. Although I didn’t do an experiment on the surface area it is clear from my research that the larger surface areas will also increase the speed of the reaction. This is because when there is a larger surface area there are more of the particles in contact with the hydrochloric acid then the smaller surface area. Because of this the hydrochloric acid can hit more of the particles.
