I am going to see how fast the CO2 is given off when I vary the amount of marble chips, therefore I can get the right amount for when I do the full experiment. I set up the apparatus, as shown below, and began the experiment.
Here are my first results, please note that the 1.25g section in italics was the set of results on the hotter day.
As I am going to use temperature as my variable, these experiments were very useful at indicating that my prediction was right. They showed that on the hotter day, even though
it had less reactant, the 1.25g experiment was faster than the 1.5g one. They also showed that the cold experiment took the longest to complete, which concurs with my prediction.
Plan
When I do the experiment, I am going to use 1.25g of calcium carbonate, and 20cm3of Hydrochloric Acid as fixed amounts; I will then vary the temperature of these in order to get my results. To keep the temperature the same both times, and in order to vary it, I will be using an ice bath to keep it cool, and a hot water bath to keep it warm.
The calcium carbonate will be measured on a set of sensitive digital scales and the acid will be measured in a measuring cylinder for maximum accuracy. In this experiment, it is important that the amounts are the same because it must be a fair test, in order to get the most accurate results possible. Throughout all of the experiments, I will be taking readings every 5 seconds, in order to get the amount of gas given off with quite small intervals between, so I can measure the rate of reaction accurately, I also did this in my preliminary experiment. When I plot these on a graph, it will show me quite well how fast the rate was, and if there were any changes and where they came.
When I have got a full set of results, I will then have to repeat these in order to make sure that none of them are anomalous. This will be a very important stage in the experiment, as it verifies the results and makes them valid.
I am going to do a minimum of 5 different temperatures, and make sure that they are repeatable. The temperatures that I am planning to investigate are 5º, 10º, Room Temperature, 20º and 30º, and then I will try and reproduce these results.
My results will be quite accurate, as I will be able to measure to 2 decimal places when weighing out the calcium carbonate, and a detailed measuring cylinder will be able to give me quite a good degree of accuracy when measuring out the 20cm3of acid. The stop clock that I shall be using also has milliseconds; therefore I will be working to a high standard of accuracy, yet I will probably not record the milliseconds.
The next page has a copy of the blank pre-prepared table I created in order to record my results easily and neatly.
Equipment
I will be using the following in my experiment:
A gas syringe to collect the CO2
A conical flask with a bung and delivery tube into the gas syringe in which to conduct the experiment
A stop clock in order to time the experiment and take readings every 5 seconds.
A heatproof mat on which to conduct the experiments so that no acid is spilt onto the work surfaces, and therefore not endangering anyone or ruining the lab equipment.
A Bunsen Burner, gauze, and tripod
A set of digital scales
A measuring cylinder
A bung and delivery tube
A stand to hold the gas syringe in place whilst collecting the carbon dioxide
A thermometer in order to measure the temperature of the acid.
Possible Variables
- The ambient temperature of the room definitely has a strong effect when investigating the rates of reaction at room temperature, as my preliminary results show.
- The surface area of the marble chips is very likely to affect the outcome of the experiment. As one of the reactants is a solid, the surface area of the solid will affect how fast the reaction goes. This is because the two types of molecule can only bump into each other at the liquid solid interface, i.e. on the surface of the solid. So the larger the surface area of the solid, the faster the reaction will be. Smaller particles have a bigger surface area than larger particle for the same mass of solid
- The concentration of the acid. Increasing the concentration of the reactants will increase the frequency of collisions between the two reactants. So this is collision theory again. Although you keep the temperature constant, kinetic theory is relevant. This is because the molecules in the reaction mixture have a range of energy levels. When collisions occur, they do not always result in a reaction. If the two colliding molecules have sufficient energy they will react.
Analysis – Post Experiment
Analysing the Data
The graphs show me exactly what I had already predicted. The higher the temperature, the faster the reaction that took place. On the graphs, the curve of the points shows me what I had expected, although a little less than I had thought. It is always steeper at the beginning than at the end, where it usually rounds off. I said in my prediction that I thought the temperature would be a major factor in the rate of reaction, and my graphs show that I was right. The graph which proved this very convincingly was the graph of rate of reaction against temperature. It shows that the higher the temperature, the faster the rate of reaction, therefore proving me right.
I took the results for the first and repeat experiments, and averaged them. This graph represents the averages of the two. As you can see, the results are pretty good, but with a couple of anomalous points in there too.
Explanation of Results
The best explanation for this is to state the Collision Theory once more, and the Maxwell Boltzmann Theory as well.
The Collision Theory explains how chemical reactions take place and why rates of reaction alter. For a reaction to occur the reactant particles must collide. Only a certain fraction of the total collisions cause chemical change; these are called successful collisions. The successful collisions have sufficient energy (activation energy) at the moment of impact to break the existing bonds and form new bonds, resulting in the products of the reaction. Increasing the concentration of the reactants and raising the temperature bring about more collisions and therefore more successful collisions, increasing the rate of reaction.
This is obviously very relevant to my experiment, and it talks about how and why the rate of reaction increases.
The next thing to explain my results with is the Maxwell Boltzmann Distribution Theory. The diagram shows the relationship between the temperature, and the speed of the reaction.
Results
The next few pages will be dedicated to showing the graphs that I have created to represent my results. All of the graphs have been made from the averages of the first and repeat experiments, therefore partially cancelling out any anomalous points from the readings. Below is the graph showing the relationship between the rate of reaction and the temperature, which is a very useful graph for this experiment.
These graphs are very good indicators of how the experiment went, and what the outcome was like. I mentioned before my worry over variables, but I am sure that none of these will have made a significant impact on my results.
