- Never run around in the lab
- Make sure all bags and stools are tucked away and not blocking pathways
- Ensure we can move away easily form an experiment by standing up when carrying it out.
Variables
This experiment will include many different variables that I will need to identify to ensure my experiment is fair. The different variables which may affect the experiment are:
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Temperature – Temperature increase will increase the rate of reaction.
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Size of marble chips – different sized chips will cause the rate of reaction to differ.
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Concentration of acid – if the solution is more concentrated the rate of reaction is faster.
Throughout this experiment, the only variable I will alter will be the concentration of hydrochloric acid. This is because I want to investigate how changing the concentration of acid will affect the amount of Carbon Dioxide released.
I will use a constant size of medium marble chips, between 6 and 9 millimetres because these react quick enough but not too quickly to allow me to take readings.
To ensure the experiment is fair, I will have to control the temperature of the experiment, to stop it affecting the results. I will try to keep the temperature low by carrying out the experiment in the same room, on the same day.
I will also use the same acid throughout, hydrochloric acid, and always ensure the measuring cylinder is full or has the same volume to begin with.
Prediction
I predict that the largest and quickest yield of Carbon Dioxide will be produced when the most concentrated hydrochloric solution, 40cm³ acid and 10cm³ water, will be added to the Calcium Carbonate.
This is because of the collision theory. In order for two things to react they must collide with each other. They must also collide with a certain amount of energy. This is called activation energy which is required to start a reaction. Anything which increases the number of collisions or lowers this activation energy is going to make the rate of reaction quicker.
With the concentration of the acid at its maximum there are more reactants and molecules, which collide together. So if there are more collisions. The reaction will be faster and therefore produce more Carbon Dioxide.
Low Concentration High Concentration
As you can see above, the particles in a low concentration are more spaced out and there are fewer of them. However reactants in a higher concentration have more particles, closer together. This means there is a higher chance of calcium carbonate particles colliding with hydrochloric acid and increasing the rate of reaction.
I also think that as the reaction goes on the rate of the reaction should begin to decrease because the reactants are turning in to products, therefore my graph will have a slight curve. This is because as the reaction proceed, some of the reactants are changed in to products which causes the concentration of the reactants that remain to become lower and lower. As a result the reaction becomes slower and slower and stops when all the reactants have been changed to products. ³So as the reaction time increases hydrochloric acid and calcium carbonate will have reacted and turned in to water, calcium chloride and calcium carbonate, therefore slowing the reaction down.
There are also other factors which can affect the rate of a reaction, such as the size of chips and temperature. The following diagrams show Calcium Carbonate (marble chips) reacting with Hydrochloric Acid.
Large Surface Area Small Surface Area
There are 8 particles in contact There are 16 particles in
with the marble chip. contact with the marble chip.
Reactions with solids occur on the surface. The smaller the particle, the larger the surface area. A smaller piece of marble chip will react quicker with Hydrochloric Acid as it has a larger surface area. A larger piece of marble will react slower with Hydrochloric Acid because it has a smaller surface area. As we can see in the above diagram there is twice as much acid in contact with the small marble chips than the large ones. If there are more particles, more collisions occur and the rate of reaction increases.
Another factor which may affect the rate of reaction is its temperature.
Low Temperature High Temperature
An increase in temperature will increase the rate of the reaction. This is because particles have more energy when they are heated causing them to move around more. This results in more collisions and more collisions between particles means a faster reaction.
Preliminary Work
For my preliminary work I will carry out an experiment using the same apparatus set up in the same way however I will investigate which sized chips produce the largest yield of Carbon Dioxide. I will use 5 grams of Calcium Carbonate and 20cm³ of Hydrochloric Acid.
Results
Conclusion
The graph shows that the smaller chips are the quickest to react and give of the most Carbon Dioxide. The graph is steep in the first 10 seconds because there are more reactants to collide with each other however later on they have turned in to products.
For my actual experiment I am going to use medium sized chips because my preliminary work has allowed me to find out these are the most efficient. I chose medium chips because they should produce Carbon Dioxide at a good pace for me to be able to take readings easily, unlike small chips which have a massive surface area and react too quickly.
Analysis
When plotting my graphs, I decided to plot four different graphs – 1 for each type of acid used and 1 for the averages in each experiment. My graphs are plotted through the origin because I began timing my readings from zero so therefore my graphs must begin from zero.
My graphs did show a few anomalous results, which I have circled, but by calculating the averages the results become slightly more accurate. These may have been caused by human error when taking down the readings or gas may have escaped from the thistle funnel. The mass of the marble chips may also be slightly in accurate as we measured them as close to 5 grams as possible but not always exactly. Another possibility is because although I used medium sized chips they ranged in size from 6-9mm, so the surface areas could be slightly different which may account for a margin of error.
Each graph increases rapidly to between 50 and 70cm³ of Carbon Dioxide produced in the first 10 seconds and then steadily increases. However, the higher the concentration of acid, the more Carbon Dioxide is produced. This proves that my prediction was correct. Looking at the graph of averages shows how each experiments maximum production of gas decreases as the amount of Hydrochloric Acid used decreases. For example, using 40cm³ of Hydrochloric Acid produces a maximum yield of 148cm³ of Carbon Dioxide in 2 minutes. However, using 20cm³ of acid only produces 113cm³ of gas in the same amount of time. My prediction that 40cm³ acid and 10cm³ water would produce the largest amount of Carbon dioxide is correct because, as I stated in my plan, there are more reactants and molecules to collide with each other and if there are more collisions, the rate of reaction increases.
Hydrochloric Acid is a strong acid and by adding water to it, does not make it a weak acid but become weaker than the previous acid used.
To work out the rate of reaction I will use the formula
Rate of Reaction = Volume of Gas produced
Time taken
I will work out the rate of reaction for the first 10 seconds of each concentration, using the average results.
I have also worked out the rate of reaction for the last 10 seconds of each concentration, using the average results.
The tables above prove the prediction I made in my plan that the rate of reaction will decrease as the reactions proceed to be correct. The tables show that the rate of reaction is much slower in the last 10 seconds than the first 10 seconds. For example, using 40cm³ of acid, in the first 10 seconds 5.8cm³ of acid was produced per second however in the last 10 seconds only 1.2cm³ of acid was produced per second. My prediction was correct because the experiment reacts quickly in the first 10 seconds because there are many reactants colliding with each other, however in the last 10 seconds many of the reactants have been turned into products, and therefore slows the reaction down.
Evaluation
I think that my experiment went well because my results did turn out as I expected and I think they are as accurate as they could be even though we used old resources. Although my results were good I also calculated averages to try to eliminate any other errors and make my results as accurate as possible. However my experiment did have a few anomalous results. For example, the points I have circled on my averages graph seem to be anomalous because it would not be expected that a lower concentration would produce more acid in the first 10 seconds than higher concentrations. These may have been caused by an error when plotting the graphs and drawing the curves, by the temperature increasing the rate of reaction or an error when noting down the readings.
My method was suitable for this experiment because there was limited equipment and time available and the experiment did show a relationship between concentration and gas production. However there were problems with the experiment. Firstly, when turning the cylinder upside down a small volume of water was lost which may have affected my results. The volume of the cylinder was constantly changing and the cylinders were old which made it difficult to take readings. I also had trouble in reading the measurements on the gas syringe between 60 and 80 cm3. This was because the arms of the clamp had a hold on the syringe and I could not see the measurement lines. To rectify this problem we simply crouched and read the measurement from underneath but it some slight errors may have been made. In addition, a slight margin of error may have been caused by the thistle funnel because it was not always effective in letting the gas through and a small amount of gas may have escaped before covering the top of the funnel. Another factor which would have affected my results would be using different concentrations of Hydrochloric Acid; however I did not do this.
If I was to carry out this experiment again I would use a burette or pipette to measure the amount of Carbon Dioxide produced because they are more accurate than a measuring cylinder. This is because the volume of water would be the same each time because water is not lost as pipette/burettes do not need turning upside down. The surface area of the marble chips was not perfect because they ranged from 6 to 9 mm. The experiment could have been improved if I had used powdered marble chips because the surface area of each weight of powder would have been a lot similar. However if I did use the powdered chips, the concentration of acid may have had to be weakened, as the reaction would have taken place a lot quicker due to the very large surface area and readings may not have been as accurate. I would also make sure all my equipment was as new as possible and worked correctly.
To improve my experiment further or find out if the rate of reaction did slow down I would carry out the experiment for longer than 2 minutes to see if a pattern emerges. What's more, I could repeat each volume to allow me to calculate an average which remove most of the errors and improve my experiment further.
To back up my results I could carry out another experiment however this time investigating a different factor which affects the rate of reaction, such as temperature or using a catalyst to speed up the rate of reaction.
To investigate temperature every other variable must be kept constant and only the temperature be altered. If I was to carry out this experiment I would use the apparatus I have used in this experiment, set up in the same way. To change the temperature I could place the conical flask in a warm water bath to increase it and ice bucket to decrease it. Readings would be taken of the amount of Caron Dioxide produced at different temperatures, such as 50°C, 60°C, 70°C and 80°C. The experiment should be repeated several times to ensure the results are accurate and averages can be calculated.
If the experiment goes correctly as the temperature increases the rate of reaction should also increase because when particles are heated they have more energy causing them to move around more. This results in more collisions and increases the rate of reaction.
