Calcium Carbonate (s) + Hydrochloric Acid (aq) water (l) + Carbon Dioxide (g) + Calcium Chloride (aq)
CaCO3 + 2HCl CaCl2 + H20 + CO2
What I will be studying is the rate of reaction, by seeing how much carbon dioxide is produced as you increase the concentration.
Equipment I Will Use
In this experiment, I will use the following apparatus:
- One conical flask with side-arm
- One container (Filled with water)
- Various measuring cylinders to measure the solutions out, and to collect the gas
- One stand with boss and clamp
- Hydrochloric Acid
- Water
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5g of small CaCO3 chips
- Set of scales accurate to 0.01g
- Stopwatch
10. Safety goggles (due to acid being used)
What I Will Do
The first thing I will do, Is to measure out 5g of the marble chips. They will be small chips, to get a good surface area. After I have done this, I will measure out a 20cm3 solution using the measuring cylinders. I have chosen to use a scale of 0m to 2m for my acid concentrations, as I think that this will give me a wide variety of results to study and analyse. The next thing I will do is to fill the container with water. Then, a measuring cylinder will be filled with water and then turned upside down in the container full of water. The tube from the flask is then fed into the measuring cylinder filled with water. After the apparatus has been set up, I will place the chips into the flask and then the solution will be poured in, and the rubber bung securely pushed into the top. Someone then will start a stopwatch and after 30 seconds, I will take a reading from the measuring cylinder as to how much Carbon Dioxide I had collected.
This method works, as the gas is lighter than water, so the gas moves up through the water to the top of the measuring cylinder, and forces the water out. I always had to keep the amount of chips, and the size of chips the same, as to make it a fair test. The readings will betaken a few times to get an average.
Below, shows a diagram of the setup I will use.
How Experiment will work
My Variables And Safety Aspects Of The Experiment
As I have already mentioned, the variable that I will be changing in this experiment, is the concentration of the acid solution. All the time, the solution will always be 20 cm3. I will use the following concentrations:
This range of solutions, should give me good results to analyse.
There is a safety aspect of the experiment, as I am using acid. If this goes into my eyes, or anyone else’s eyes, it will hurt very much and cause a lot of damage. This is why I will wear safety goggles. Also, if there are a large number of people working in close proximity to one another, accidents can happen, so we will be working spaced out, to avoid collisions.
What I Think Will Happen
Based on knowledge, I have made a series of predictions as to what will happen in my experiment:
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As the concentration gets higher/stronger, I will collect more gas (CO2). This is because more collisions will be taking placing due to there being more acid particles to collide with the Calcium Carbonate.
- As the concentration of the solution gets lower/weaker, there will be less gas to collect, due to there being less collisions between the Calcium Carbonate and the acid particles.
- The higher/stronger the concentration, the larger the rate of reaction will be, due to there being more reactive particles (in the form of the acid) to collide frequently and faster with the Calcium Carbonate. Therefore, I should get more Carbon Dioxide.
- The lower/weaker the concentration, the smaller the rate of reaction will be, due to there being less reactive particles (in the form of the acid again) to collide frequently and faster with the Calcium Carbonate. Therefore, I should collect less Carbon Dioxide.
The Experiment
I did, carry out a trial experiment, in which I found that the 5g of Calcium Carbonate I was using was sufficient to gain good results. I did, however, find that the measuring cylinder that I was using to collect the gas had a too big a scale to measure the amount of gas on the lower concentrations. I learnt from this and decided that in the actual experiment to use a cylinder with a smaller scale. This also lowers the margin of error when reading the results.
My Experiment Results
Below is a table showing the results that I collected. As you can see, I chose to do three separate experiments and then get the average of all of the results. Immediately, you can see that my predictions are in tune with my results, as the higher the concentration, the more gas produced., and the higher the reaction time. This is because; the rate of reaction is affected by the number of acid molecules in the solution. Due to their being more acid particles in a higher concentration, there are more collisions.
Analysing My Results
The table above, shows the results that I collected and how they are numerically correct with my predictions, i.e. as the concentration gets higher so does the reaction rate. Although this is true, we cannot see to what extent this is without graphs, so below are 2 graphs showing results.
This graph shows that the more concentrated the solution is, the more gas is produced, due to more successful reactions between the acid and the calcium carbonate.
The pattern that is formed is not a straight line, (which would have suggested that reaction rate is directionally proportional to concentration) but a smooth curve. What this suggests, is that a small increase in concentration, can lead to a drastic change in reaction rate.
The second graph above shows the concentration of the solution used against the reaction rate. From studying this, we can again see that it is a curve and not a straight line. As we saw in the first graph, a small change in concentration can lead to a large change in the reaction rate.
In the weaker concentrated solution there is a slower rate of reaction. This is because there are less HCl particles than water particles. Because of this, the solution is less reactive. This means that there are fewer collisions between the Calcium Carbonate and the acid particles
In the more concentrated solutions we can see a faster rate of reaction. This is because the opposite is taking place to what happens in the lower concentrations. There are more acid particles, so fewer collisions take place. For this reason, the solution is more reactive. This is why when we put chips into just water (0m) we collected hardly any Carbon Dioxide, and that when chips were placed into pure acid, we collected a lot of gas.
Evaluation
I think that the experiment that I did was a success in the sense that I got readings that I could analyse and bring together a conclusion. The trial that I carried out was a good idea, because it highlighted a number of errors in my original plan. The biggest error it outlined was that the tubes that I was to collect the gas in were too big, and I couldn’t get a reading due to too little gas being produced. I changed this in my actual experiment, to smaller tubes, to make my readings more accurate.
My results on the graphs are pretty accurate and all of the points are on the line, or very slightly out. I think that this is to be expected with the equipment we were using, as it wasn’t the most state of the art. Despite this, I think that I collected very valuable data, which was reliable too.
There may have been a small margin of error, when I was timing the thirty seconds. Firstly, the stopwatch was started when all the solution had been poured in. This may have led to gas being produced as soon as the liquid hits the calcium carbonate, and therefore we would get a small margin of error. The same reason applies to at the end of the thirty seconds. When the thirty seconds were up, the tube that delivered the gas to the upturned test tube, may have not been pulled out immediately, so more gas may have leaked through. These errors, are very small, so I don’t think that I should be worrying about them that much.
An improvement to my experiment could be that next time, I could use a gas syringe. We used a measuring cylinder to collect the CO2 for this experiment, and so we had to clamp it into place in the water. This could have led to a discrepancy, as the tube may have been slanted a bit, and therefore, the reading taken would have been slightly out. A gas syringe is more accurate, as the scale in smaller, and the friction is so little, that the smallest amount of gas can be read. We could also use different acids and compare that data with this data.
Altogether, I feel that the experiments carried out were successful and that I fully exploited my task. My predictions were in line with my final results, and the tables and graphs show this. The trial experiment showed me the problems with my original plan, and the changes made were successful. From this, I can conclude that the experiment was a success.
