- Repeat all experiments 3 times
Prediction:
I predict that the outcome of the experiment involving a reaction between marble chips and dilute acid will be that as the concentration is increased, so will the rate of reaction. This is because, if it is of a higher concentration, there will be less water particles acting as obstacles and more nitric acid particles to collide with the marble chips, therefore more collisions are successful. If the concentration is lower, there will be more water particles to get in the way of the nitric acid particles therefore it would become more difficult for them to collide with the marble chips and so less collisions will be successful. Also, I think there will be a regular pattern between
Preliminary Tests:
From the preliminary results I have obtained, I have decided the majority of the combination I originally choose is applicable and offers good results. The chosen concentration works well as is the range between the highest and the lowest
Results Set 1:
Results: Set 2
Averages:
Average Rates of Reaction:
To find the average I will have to use the following equation:
Volume (cm³)
Time (s)
Analysis:
From the experiment of reacting marble chips and dilute nitric acid I have conducted, I have discovered that, generally, as the concentration increases, so does the rate of reaction. By using my graph and average results, I can see there is a steady pattern and so therefore, my prediction is correct because there are few anomalous results, all of which I have stated in my evaluation. The steeper the curve of the line is, the quicker the rate of reaction. The steepest line is that of the highest concentration and the flattest line belongs to the 0.4M concentration which obviously has the slowest reaction rate. The 1.6M, 1.2M and 0.8M concentrations all fit between these points with 1.6 having the second most fastest reaction time, 1.2 being third quickest and 0.8 being second slowest. When the concentration is higher there are more nitric acid particles as opposed to a smaller number of water particles which means there are more nitric particles to collide with the marble chips and also it is easier for the nitric acid particles to reach the marble chips and collide with them. This meant that more gas was produced. When the concentration is lower, there are less acid particles compared to that of the water particles, so there are less collisions between the marble chips and the nitric acid particles. This means that less gas is produced. This was what I prophesised in my prediction when I stated that “as the concentration is increased, so will the rate of reaction”. By using my graph, I have also found out that as the concentration doubles, so does the rate of reaction in some cases.
For example:
When the concentration is 0.6M at 10 seconds, the volume of gas produced is 9.5cm³.
When the concentration is 0.8M at 10 seconds, the volume of gas produced is 4.75cm³.
(2 x 4.75 = 9.5)
When the concentration is 0.4M at 30 seconds the volume of gas produced is 7.75cm³.
When the concentration is doubled at 0.8M the volume of gas produced is 15.5cm³
(2 x 7.75 = 15.5)
But this is not correct for all my results.
For example:
When the concentration is 1.6M at 30 seconds the volume of gas produced is 27cm³.
When the concentration is halved at 0.8M the volume of gas produced is 15.5cm³.
(2 x 15.5 should equal 31, not 27)
When the concentration is 0.8M at 30 seconds, the volume of gas produced is 15.5cm³.
When the concentration is 0.4 at 30 seconds, the volume of gas produced is 6.9cm³.
(6.0 x 2 = 13.8 which is almost 15.5)
This makes my prediction very accurate as generally there are few points that do not follow the pattern of when the concentration increases so does the rate of reaction, neither are there that do not double as the concentration is doubled. This is because if concentration is double so is the amount of nitric acid particles and as a result there should be twice as many successful collisions between the marble chips and the nitric acid particles. This means the rate of reaction will be twice as fast.
Although, due to my correct prediction and mostly correct graph and results, my experiment was quite accurate, the experiment could have been much more accurate if I had done many more repeats which would back up my conclusion more so and also if I had tested over factors such as surface area, temperature and added a catalyst. I will discuss this to more depth in my evaluation.
Although there may have been some experimental error, which I have discussed in my evaluation, my conclusion is accurate because it is a high majority of results that agree with my prediction and so if a huge error occurred during the experiment, my results would not follow a steady pattern. An example of this experimental error is that it was only in few cases did the rate of reaction double as the concentration doubled.
The graph on the next page backs up my conclusion very well as the line of best fit follows a steady pattern mostly, except a few anomalous points which I have pointed out in my evaluation.
Evaluation:
The experiment I have conducted involving the reaction between calcium carbonate and different concentrations of nitric acid has well as well as bad points in terms of method and results.
My graph shows a maximum of 8 anomalous results; in the period of 0 to 40 seconds, for 0.8M and 1.2M concentrations, results are irregular and anomalous, therefore this section of my results cannot be justified as accurate. Apart from this, my lines of best-fit fits carefully on each graph. The rest of the points are quite reliable although they could be more accurate.
There are both minor and major factors that could have affected my results.
Although the measuring cylinders used were of the right size for the measurements needed, the use of burettes would have made my experiment of a higher standard of accuracy because they record each measurement to every 0.1cm, as opposed to every 1.0 in measuring cylinders. Measuring cylinders are quite inaccurate and the scales are often different and not as reliable which is a problem as even the slightest fraction of more or less nitric acid or water could change the concentrations. If just one particle more is present one more collision would occur which could actually increase the rate of reaction by a fraction, making the final results less accurate.
An unwanted catalyst could have also been present when conducting the experiment, if any of the equipment was contaminated, but this is highly unlikely as each piece of equipment used was thoroughly cleaned.
The temperature for each individual experiment was obviously not exactly the same and so this could have affected the experiment by increasing or decreasing the rate of reaction. The use of a water bath would have made the experiment more accurate because the temperature could have been set to 25° making the experiment much more fair. The increase in temperature could also mean that the rate of reaction for each experiment would have been increased as the increase in temperature means the nitric acid particles gain more energy and vibrate quicker, colliding faster and more successfully with the marble chips.
The fact that no individual marble chip had exactly the same weight and surface area could have caused problems. If chips in the first set of experiments were larger than them of the second, it could mean that the rate of reaction in the second set was quicker as there are less ‘layers of particles’ in each chip, so it would be quicker and easier for the nitric acid particles to have access to collide with each individual particle in the marble chip because the larger the surface area the quicker the rate of reaction. One way to get around this would be to use calcium carbonate in powder form because the surface areas have all particles are the same, except for extremely minor fractions but, using the same concentrations, it would mean that the reaction would occur too fast and so the concentrations must be changed. A new set of measurements that could be used are;
1.0M (25cm³ acid, 0cm³ water)
0.8M (20cm³ acid, 5cm³ water)
0.6M (15cm³ acid, 10cm³ water)
0.4M (10cm³ acid, 15cm³ water)
0.2M (5cm³ acid, 20cm³ water)
Also on some experiments, for example the 1.2M and 0.4 concentrations of each set of experiments excluding preliminary, the gas syringe stuck which could mean that some results are incorrect such as at 50 seconds on 1.2M and the stand which held the gas syringe was quite unstable and because of it, it was extremely difficult to ensure the syringe was parallel with the table and the gas syringe would most likely be on a slant and so this could make it move slightly faster or slower by the force of gravity acting upon it.
Another factor that could be the reason why I have anomalous results is the time when the bung is placed on the conical flask compared to when the stop clock starts. Below is a design that aims to conquer this problem by the stop clock starting at the exact same time the bung is placed on the conical flask:
To operate it, you must pour the solution in to the upside-down conical flask (the nitric acid solution) then pour this into the tubing and lift the bung up to place the marble chips inside the other conical flask. When you press the stopwatch button, the nitric acid flows into the other conical flask containing the marble chips at the same time as the timer begins.
From my evaluation, the following is an improved method of how I would conduct my experiment if I were to do it again:
- Using a burette, measure out nitric acid into a test-tube using the measurement of 25cm³ of Nitric Acid and add 4.0g of calcium carbonate in powder form.
-
Switch the water bath to 30°C and place each test tube in there
- Leave each test tube in the water bath for thirty minutes whilst you set up the experiment as shown in the diagram
- After this, take the 1.0M labelled test tube and empty the contents into the conical flask of the apparatus
- Press the timer so at the same time the nitric acid solution runs into the conical flask containing the marble chips
- Every 10 seconds for a period of 100 seconds, measure the volume of the gas syringe
-
Repeat this for 0.8M, 0.6M, 0.4M, 0.2M concentrations
If I had a longer period of time to conduct the experiment of reacting marble chips with dilute acid, I would have adapted the following and fit it into a new method whilst still using the same apparatus to expand my knowledge of rates of reaction even more so:
- Temperature: I would alter the temperature to a lower and higher degrees to see how this affected the different rates
- Surface Area: I would use a powder form of marble and a larger rock to compare the results
- Catalyst: I may add a catalyst to see if it affects the volume and speed of gas produced
- Concentration: Also I would use a different concentration such as the following to see if the pattern is still the same:
It would also have been possible to use a different acid such as Sulphuric acid instead of Nitric acid to compare the different results if there are any. Also, more repeats would have helped me to come to a more definite conclusion.
I conclude that all of the above things stated in my evaluation would help me to test rates of reactions in other areas, therefore developing my understanding and widening my knowledge of the topic.
