AIM
I am going to investigate how the concentration of the solution will effect the rate of reaction when calcium carbonate reacts with hydrochloric acid. The equation for this reaction is:
Calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
CaCO (s) + 2Cl (aq) → CAcl (aq) + H 0(aq) + CO (g)
To measure the rate of reaction I will measure how much gas is being given off rather than measure the increasing/decreasing mass of the reaction.
When I have obtained my results I will then use this equation to work out the average rate of the reactions:
VARIALBES
The five variables concerned with this investigation are (as described in the introduction):
Temperature
Concentration
Surface Area
Amount
Catalysts
In this investigation I will not be using catalysts.
The temperature for this investigation should be approximately 23°C which is the room temperature.
As I am investigating the concentration (input variable) to insure that the test is fair I will keep the three other variables temperature, surface area, and amount (the controlled variables) constant throughout the whole investigation. My dependant variable is the rate of reaction because this is what will be changing as a consequence of the changing concentrations.
PREDICTION
I predict that the more concentrated a solution is the faster the rate of a reaction will be and therefore a higher amount of gas will be given off in a certain period of time.
This is because the more concentrated a solution is the more particles there are so there will be more frequent collisions between the different atoms, unlike in a more dilute solution.
The acid particles will move randomly around. As the concentration is increased there are more particles in the same volume. Therefore, there is a greater chance of acid particles colliding on the marble chip surface, and reacting, so more concentrated solutions will have a much higher rate of reaction.
I also predict that the end result will look similar to this – predicted graph:
Nearer the beginning of the reaction it will be reacting fastest because this is when the products are in abundance. The reaction will then beginning to slow down as the products get used up over as the reaction progresses. When one of both of the products is completely used up the reactions will obviously stop.
PRELIMINARY WORK
For my investigation I will be using medium sized marble chips. However, I now need to carry out some preliminary work to find out what amount of marble chip to use, and to decide what time range and intervals to measure the volume of gas given off at, for my actual investigation and experiment.
I will record the volume of gas given off at one minute intervals over a period of five minutes.
The table below shows the results of 5g of calcium carbonate medium sized chips in 50ml of 0.5M solution.
The table below shows the results of 4g of calcium carbonate medium sized chips in 50ml of 0.5M solution.
The table below shows the results of 3g of calcium carbonate medium sized chips in 50ml of 0.5M solution.
The graph below simply shows the increasing amount of volume of gas for each different amount of marble chips:
After five minutes, 3g releases averagely 69CO2/cm ³, 4g releases averagely 150.5 CO2/cm ³ and 5g releases averagely 185 CO2/cm ³. Both 4g and 5g quite quickly in a dilute 0.5M solution - as they give off too much gas in five minutes so I will use 3g for the experiment.
I will now clarify if 3g is the right amount to choose by trying it in 50ml of a 1M solution and 2M solution to get an idea of how quickly it reacts:
- After five minutes the amount of gas released in a 1M solution was 243CO/cm ³ and in a 2M solution it was 462CO2/cm ³.
3g also gives off quite a lot of gas in the more concentrated solutions. This shows that 3g also reacts too fast so I will again decrease the amount of calcium carbonate.
I will now try 1g of calcium carbonate in 50ml of a 2M solution to get an idea of how quickly it reacts:
- After five minutes in a 1M solution the amount of gas released was 65CO2/cm ³ and after five minutes in a 2M solution there was 157CO2/cm ³.
For my actual investigation I will need to collect around at least eight results for a more accurate conclusion. I will do this by measuring the volume of gas at 30 second intervals over a period of five minutes; this will give me ten results. From my preliminary work I have gathered that using 1g of medium sized marble chips is the most reasonable amount to use in the actual investigation because it does not react too quickly so it will give me a good number of results to conclude from. As I have used 50ml of hydrochloric acid so far I will continue to do this in the actual experiment. From the preliminary work I have also decided that I will also repeat the experiment three times, instead of once, using each concentration of solution for more reliable results.
METHOD
During the preliminary work I used a bowl filled with water, a tube connected to a conical flask that went into measuring cylinders filled with water and turned upside down in the bowl, to measure the amount of gas given off. As the gas is released in the conical flask it travels through the tube and fills up in the measuring cylinder, as it does so the water in the measuring cylinder decreases and this is how the amount of gas can be seen on the measuring cylinder. When one measuring cylinder gets filled up with gas another one, filled with water, must be ready at hand to quickly replace it. When replacing a measuring cylinder the end of the tube must be blocked for that short time so no gas escapes as this would reduce the reliability of the investigation.
I will continue using this method throughout the actual investigation.
Apparatus used:
- Plastic bowl (filled with water)
- 100cm³ Measuring cylinder (filled with water)
- Conical Flask
- Bung (attached to tubing)
- Stopwatch.
The apparatus will be set up as shown in the diagram:
Steps of method:
- Measure 50cm³ of 0.5M of hydrochloric acid and pour it into the conical flask.
- Put 1g of medium sized marble chips into the acid, replace the bung on the conical flask and start the stop clock.
- Record the volume of carbon dioxide produced every thirty seconds for five minutes.
- Repeat steps 1-3 a further two times for accuracy.
- Repeat steps 1-4 again for 1M and 2M concentrations of hydrochloric acid.
I then carried out the experiment and the following results were obtained:-
Using 0.5M solution
Using 1M solution
Using 2M solution
CONCLUSION
Using the results from the tables on the previous page I can now present the data in the form of a graph:
From the line of best fit on the graph, I can see that there was an increase in the average volume of gas released over the five minutes for each solution. The 2M solution released the highest amount of gas, it released 130cm ³ of carbon dioxide at the end of five minutes. The 0.5M solution released the lowest amount of gas, it released only 26cm ³ of gas. The 1M solution released 49.7cm ³ over five minutes.
I will now work out the average rate of reaction when the concentration of a solution is increased using this equation:
Graph showing how the concentration of the solution affects the rate of reaction:
The average rate of reaction increases as the concentration of the solution increases.
These results for the rate of reaction also support the results from the graph so the more concentrated a solution is the higher the rate of reaction will be. This proves that my prediction was correct, and like I predicted, in the more concentrated solution a higher amount of gas was given off in a period of five minutes so there was a faster rate of a reaction.
The scientific theory behind this is that the more concentrated solution had more particles so there were more frequent collisions between the calcium carbonate and hydrochloric acid atoms, unlike in the more dilute solution. As the concentration is increased there are more particles in the same volume. Therefore, as the acid particles moved randomly around there is a greater chance of acid particles colliding on the marble chip surface, and reacting, so the more concentrated the solution was the higher the rate of reaction was.
My predicted graph is also quite similar to the actual graph as both graphs show an increase in the amount of gas. However, unlike my predicted graph, on my actual graph there is no definition of where the reaction begins to stop or even slow down.
EVALUATION
The procedure for this experiment was fairly straightforward and using my method I was able to gather a reasonable amount of evidence to notice relevant patterns. My method was also suitable but could have been improved by possibly using a syringe, barrette, or bigger measuring cylinder to measure the amount of gas given off. This is because when using the 100cm ³ measuring cylinder on a few occasions while using 2M solution more than 100cm ³ of gas was given off, (for example, at five minutes 130cm ³ of gas was given off ), so the measuring cylinder had to be changed during the experiment. This reduces the reliability of the experiment because some gas may have escaped when the measuring cylinder was being changed. Another factor that may have affected the fairness of the experiment was half of the experiment had to be carried out on a different day so the temperature (one of the controlled variable) may have been slightly higher or lower during the different days. Also the size of each marble chip that made up 1g was not all equal, this affects the surface area (another controlled variable for this investigation).
To increase the reliability of the investigation I could have collected more data by doing the experiment, for each concentration of solution, several more times to get a more accurate overall average. I could have done this by doing the experiment for longer than five minutes, by doing this I may have also seen the reaction beginning to slow down or even stop: Unlike my predicted graph, on my actual graph there is no definition of where the reaction begins to stop or even slow down and I may have seen this happen on the actual graph if I continued the experiment for a longer period of time. I could have also investigated more concentration of solutions, for example 1.5M and 2.5M. I would be able to depict a more profound conclusion and it would also make my conclusion more validated. Also, when calculating the average I could also have rounded it to 2 or 3 decimal places, instead of 1 decimal place, to increase the accuracy of my calculations.
However, my results seem to be accurate and there are no anomalous results according to the line of best fit on the graph. This means there was possibly the least amount of experimental errors during my experiment.