As I have confirmed that the only variable will be the concentration of the Hydrochloric Acid, I must decide on a suitable range of concentrations to use. Below is a table showing the concentrations, which I am going to use, and how to create them.
Safety
Before starting the experiment, an important aspect, which I must take into consideration, is safety. Without planning a safe method, accidents could happen, which could easily affect my results or endanger myself or others. Therefore I must set up my equipment with care, ensuring I move around the lab in an orderly manor. My hair will be tied back, and I shall wear an overall and goggles at all times to protect my eyes and clothing from spillages or breakages. If either circumstance were to occur, a teacher or supervisor would be informed immediately. All experimental equipment that I will need should be placed on a clear bench and handled with care. All chairs must be placed under desks, and all bags must be kept away from the working area. The Hydrochloric acid is very corrosive. If any if spilt it must be reported and cleaned up instantly. If any were to come into contact with my skin, I shall wash it off promptly.
If I follow this simple safety method during the investigation then my experiment will hopefully run smoothly.
Fair Test
It is important that the experiment is kept fair at all times. If not then the results are less likely to be accurate. Therefore I must ensure that I keep each factor constant, except the concentration of the hydrochloric acid. To guarantee that the factors are constant, I will take the following precautions. I will weigh all the marble chips on electronic scales. I will measure the volume of acid carefully using a measuring cylinder. I will time the interval between readings carefully using an electronic timer. Finally I will test the gas syringe before using it to ensure that it moves smoothly as the Carbon Dioxide is produced. Placing the rubber bung on the conical flask and then setting the timer before the reaction starts will be difficult, so a few cm³ of Carbon Dioxide may be lost. However if I do this as quickly as possible I may be able to overcome this problem and loose barley any CO . Doing all of this will provide that I carry out a fair experiment, which will hopefully guarantee reliable results.
Whilst obtaining my results, I will take two readings for each concentration, meaning I will have to repeat the experiment. This is useful because I will be able to find an average result, and I can also calculate any anomalous results. I must also do obvious things, like resetting the timer and the gas syringe before starting.
Prediction
I predict that as the concentration is increased, the rate of reaction will increase. However this will not continue to happen, as there must be a maximum rate of reaction, where the rate becomes one continuous reading. I also predict that it will be a fast and violent reaction, because of the size of the marble chips and the quantity of acid.
Background Knowledge
To back up my prediction I must explain why I think these things will happen. Therefore I am going to include background knowledge into how the collision theory, surface area and concentration affect the rate.
The collision Theory
Increasing the concentration increases the rate of reaction because there are more particles in the same volume of acid so therefore more collisions are able to occur every second. The reaction happens because of theses collisions. The particles move around and collide creating a reaction. The higher the concentration, the more particles, meaning the more collisions. Therefore double the concentration then you double the reaction. When the maximum rate of reaction is reached, this is when there are more substrate molecules than enzymes. The substrate molecules then have to ‘queue’ to collide, as the enzyme molecules are kept constant and so the rate of reaction cannot increase anymore.
(diagram representing the collision theory)
Breaking the marble chips (CaCO ) into smaller pieces increases the total surface area. Increasing the surface area boosts the amount of particles, which can collide with the hydrochloric acid.
(graph showing the rate of reaction)
A larger volume would also increase the rate of reaction, as there would be yet more particles to collide.
All of the above reasons back up my prediction, indicating that it is likely to be a fast and violent reaction, increasing as the concentration does.
Method
- Measure 50cm³ of dilute Hydrochloric Acid in the following concentrations, 3.0M, 2.0M, 1.5M, 1.0M, and 0.5M. Using a measuring cylinder pour each one into a conical flask.
- Set up clamp stand and firmly, but carefully; clamp the gas syringe as shown in the diagram below.
- Choose small marbles chips, of around the same size and weigh out 5.4g for each experiment.
- Add the marble chips to the acid, replacing the rubber bung as quickly as possible and then start the stop clock as soon as the bung is in place. It is important that care is taken so as little carbon dioxide as possible is lost.
- Record the volume of carbon dioxide given off every 10seconds.
- Repeat each experiment for all concentrations twice to obtain reliable results.
Apparatus
- 50cm³ of dilute hydrochloric acid – five different concentrations
- 5.4grams of small marble chips (calcium carbonate) for each concentration of acid
- 100cm³ conical flask
- 50cm³ measuring cylinder
- 100cm³ gas syringe
- Delivery tube and rubber bung
- Timer
- Clamp Stand
Diagram
This is not the only method of studying the same reaction. I could also carry out exactly the same experiment, only using different equipment. I could also carry out different experiments to investigate the change in rate of reaction. To do this I would have to change the variable. I could investigate how temperature, mass or surface area effects the reaction. Below is another way in which I could carry out this experiment.
Obtaining Evidence
Whilst carrying out the experiment I worked cautiously, carefully following the safety section in my plan. I wore goggles and an overall at all times, and made sure my hair was tied back. I worked in an orderly fashion, taking into consideration others who were working in the lab. Nothing was dropped or spilt, and any acid on my hands was washed off immediately. The bench area was kept clear and the apparatus was handled with care at all times. Working safely contributed to a set of useful and reliable results.
Whilst obtaining my results I was careful to observe the reaction. From this I can confirm that my prediction of a violent reaction was correct. The hydrochloric acid and calcium carbonate fizzed and bubbled as the reacted. The reaction became more and more violent as the concentration of acid became stronger.
The readings, which I took, were sufficient and accurate. I was able to set the timer without loosing more than 1cm³ of carbon dioxide. I recorded each reading after exactly 10 seconds, meaning I obtained reliable and accurate results. There were no anomalous results, except for a few readings when the concentration was at 0.5Mol/dm³ (highlighted in green). These were only one reading out of sync, maybe two, on the graph. Therefore this had no effect on the results as they all followed the same line of best fit. A misreading of the gas syringe or timer could have easily caused the few ‘off’ results. If they had been more obvious and strange results then I would have considered either a change in temperature, the conical flask being moved and interfering with the reaction or an incorrect measurement in either the hydrochloric acid or calcium carbonate.
Results
Concentration – 3.0 Mol/dm³
Average Rate of Reaction: 5.2 cm³/sec
54 10 = 5.4 5.4 + 5.0 = 10.4
→
100 20 = 5.0 10.4 2 = 5.2
Concentration – 2.0 Mol/dm³
Average Rate of Reaction: 3.8 cm³/sec
38 10 = 3.8
Concentration – 1.5 Mol/dm³
Average Rate of Reaction: 2.9 cm³/sec
88 30 = 2.9
Concentration – 1.0 Mol/dm³
Average Rate of Reaction: 1.8 cm³/sec
71 40 = 1.8
Concentration – 0.5 Mol/dm³
Average Rate of Reaction: 0.7 cm³/sec
40 60 = 0.67 (to one decimal place = 0.7)
Rates of Reaction
Analysing Evidence
Conclusion
I can now conclude that as the concentration of hydrochloric acid increases, the rate of reaction increases. This is confirmed in the results, which I obtained during this experiment. Therefore it is correct to say that when there are more substrate molecules, more collisions can take place, creating a faster reaction. However, my results did not reach a maximum rate of reaction, indicating that a much higher concentration is needed to obtain this point.
It was also confirmed in my results that the larger the surface area, the faster the reaction. I know this because I used one medium sized marble chip in my Preliminary work, but in my final experiment I used many (depending on how many needed) small marble chips. The rate of reaction in my Preliminary work was a lot slower than that of this experiment, proving the surface area has a considerable affect.
My results agree with my prediction, showing that each factor, which I emphasised, would have an effect, did contribute to the speed of the reaction. I predicted that the bigger volume, the larger surface area and the higher concentrations would provide faster reactions. This was in fact correct because there were more substrate molecules in the same volume and a wider surface area created more particles. Making collisions more likely and more often.
Evaluating Evidence
For this particular investigation I feel that I used the best method possible, taking into consideration the equipment available and the time given. The method was simple, yet constructive and overall produced a sufficient and reliable set of results. The method was easy to follow and understand. The results were accurate and there were no anomalous results, which confirms the accuracy. This shows that the readings were taken at the right time, the gas syringe worked properly and that the conical flask was not moved during the experiment. I can also confirm that my results were reliable as they supported my prediction, allowing me to draw a liable conclusion.
If I were to carry out this experiment again then I would make various improvements. The experiment was carried out precisely and safely, so these areas would not need any adjustment. I would however, include more apparatus to obtain better and more informative results. I would keep a constant temperature. Instead of allowing the experiment to take place at room temperature, I would put the conical flask in a water bath and carry out the experiment at around 50°C. This would allow for a new area of investigation. I would however, have to keep the temperature constant, so I would need to constantly check on the water bath, placing a thermometer in both the conical flask and water bath. This would mean a specially designed bung would be needed, so that the thermometer would have a hole to go through.
To obtain even more reliable results, I would work with a partner. Then one person could take down results and look at the time, whilst the other watches the gas syringe at all times. With two people working at the same experiment it would also be easier to put the bung on the conical flask and set the timer at the same time.
If I were to extend the experiment I would use a water bath, as commented on previously, to obtain a higher temperature. I could then investigate whether the higher temperature would affect the speed of the reaction. I would also carry out more experiments, investigating different variables. This would expand my knowledge on how the rate of reaction changes and then I would be able to write a more detailed and learned investigation. Below is a diagram of the extended experiment that I would carry out, using a higher temperature.
(diagram was here)
Bibliography
Resources:
Chemistry Text book (class work only)
GCSE Bitesize Website -
