The second experiment can be compared to a similar experiment, which I’ve previously completed, where I added Calcium to varying concentrations of Hydrochloric acid. In this experiment I discovered that the stronger the acid, the faster the reaction was completed. I discovered that the greater the concentration (i.e. the more acid molecules in the solution), there is a greater number of collisions between the particles; resulting in an increased rate of reaction.
My preliminary work for the third experiment is when I did an experiment using different sized pieces of magnesium and hydrochloric acid. For this I discovered that the larger particles of magnesium took longer to react. I think this was because the larger particles had less surface area than the powder, and so there was less magnesium for the acid to react with, creating a slower reaction.
Predictions:
Experiment 1.
I predict that the higher the temperature of the acid, the faster the reaction will take place. I believe this is because of the kinetic theory, which says: the hotter the particles in the acid the more energy they will have, and therefore will move around faster. Thus colliding with more Calcium Carbonate molecules and colliding more quickly, causing the reaction to occur at a faster rate.
Experiment 2.
I predict that in this experiment, the more concentrated the Hydrochloric acid is, the faster the reaction will be. This is because according to what the kinetic theory says: the higher the concentration of acid, the higher the number acid molecules in the solution. Meaning that there are more acid molecules to react with the calcium carbonate molecules, and so the reaction will be higher.
Experiment 3.
In this experiment I predict that the substance that has undergone the biggest change will be the one that takes the longest to react. I believe that Calcium Carbonate in the form of Limestone will react faster than Marble, and that Chalk will react even faster than Limestone. I say this because when the sedimentary form of Calcium Carbonate (chalk) goes through the pressure and heat of being forced down into the earth, the Calcium Carbonate molecules make stronger bonds, and more time will be required to break them down.
CaCO3 + 2HCl CaCl2 + H2O + CO2
Diagrams: Experiment 1.
Experiment 2.
Experiment 3.
Method 1: For this experiment, we carefully measured 40ml of Hydrochloric acid using a measuring cylinder, and 0.5g of calcium carbonate in the form of chalk, using electronic scales. We agreed on using chalk, as it was the easiest to obtain an accurate mass of for the experiment. The acid was then poured into a conical flask and heated on a tripod and gauze using a Bunsen burner underneath. We measured the temperature of the acid using a thermometer and removed the heat so that the acid would reach the target temperature. When it reached as near the target temperature as we could possibly get it we added the chalk. A stopwatch was used to time when the chalk hit the acid to when the reaction was complete, once the fizzing had completely ceased. We repeated these procedures three times for each temperature, to gain averages obtain better, more accurate results. The mass of chalk was kept at a constant 0.5g, and volume of acid was kept at a constant 40ml to make certain the test was fair. The acid was kept at the same concentration, and chalk was always the same type of calcium carbonate used, again to guarantee that the test was kept fair.
Method 2: For our second experiment, we carefully measured 40ml of water, using a measuring cylinder, and added the 0.5g of calcium carbonate (chalk). We then proceeded to time the reaction length. For the next measurement, we measured out 10ml of hydrochloric acid and added to it 30ml of water, to make 40ml of very dilute acid, we again added the 0.5g of chalk and timed the reaction using a stopwatch. We then continued with this process, increasing the volume of acid by 10ml and reducing the volume of water by 10ml and timing the reaction with the chalk, until we ended up with 40ml of pure Hydrochloric acid. The acid was always at room temperature to maintain a fair test. Again we repeated each experiment three times and used averages to gain more accurate and truthful results.
Method 3: For the third experiment, we again carefully measured out 40ml of Hydrochloric acid using a measuring cylinder and cautiously poured it into a conical flask. Then we added 0.5g of calcium carbonate, which was carefully weighted on electronic scales in the form of chalk. We added the chalk to the acid and recorded how long the reaction took using a stopwatch. We then did the exact same thing, but this time measured out 0.5g of calcium carbonate in it sedimentary rock form of limestone, instead of chalk. The time of the reaction was again recorded using a stopwatch. Then we the exact same thing but instead used 0.5g of marble, which is the metamorphic rock form of calcium carbonate, instead of limestone. We repeated each experiment three times and worked out the average reaction time to gain a fairer, more accurate result. The volume of the Hydrochloric acid was kept at a constant 40ml and room temperature, and the mass of the calcium carbonate kept at 0.5g throughout each of the experiments, again to ensure fair tests.
Conclusion: When looking at the graph I created for the results of the first experiment, we can clearly see that the reaction times decrease as the temperature of the acid increases. This agrees with my suggestion in the prediction and therefore proves it to be correct. According to the kinetic theory, as more heat is added to the acid, the acid molecules have more energy and move around and vibrate faster. When reacting with calcium carbonate there are more collisions of the two types of molecules (which is what causes a reaction), due to the acid molecules moving faster. This also means that the acid molecules are more likely to react because the particles move about with more energy. From my graph you can see that as the temperature of the acid increases so does the speed of the reaction, but not proportionally.
You can see from my graph of results from the second experiment that there is an even bigger change in the rate of reaction. This again agrees with my prediction. I believe that this is because of the kinetic theory, which states; as the concentration of acid increases so does the rate of reaction, this is because there are more acid molecules in the more concentrated solution. Therefore, more collisions will occur between the molecules and so the reaction will take less time. Using my graph I have proved that a more concentrated acid will lower the reaction time.
In the third experiment my graph shows a big change in the reaction times of chalk, limestone and marble. The time difference between the marble and limestone is not very large, only approximately 3 seconds, but there is a difference of over 11 seconds between the reaction times of marble and chalk, which is a huge difference. I believe that this is because the surface area of the marble and limestone were quite similar, giving them quite similar reaction times. While with chalk the surface area is much greater than that of marble or limestone because it is a powder and can separate and spread out. The larger surface area means that there are more calcium carbonate molecules present in the reaction at the same time for the acid molecules to collide with. Thus causing a greater rate of reaction. Even though I said that limestone and marble have similar surface areas they still reacted at different speeds. This, I believe, is because of what I said in my prediction; that the structures of marble and limestone are different. Limestone is a sedimentary rock, and is formed when chalk is put under pressure. Marble, on the other hand, is limestone that has been placed under great pressure and heat. This means that limestone has stronger bonds than chalk and is harder to break down, and marble has been created with much stronger bonds than limestone. The activation energy needed to break the bonds of marble needs to be a lot higher than that needed for limestone. This is why marble took longer to react than limestone, because it needed more time to be broken down. These are also the reasons why there is such a large difference in my results, because there are two factors that affect the rate of reaction between limestone and chalk, but with limestone and marble there is only one.
In conclusion to my experiments I have discovered that there is at least three factors that can affect the rate of a reaction:
- The temperature the reaction takes place at.
- The concentration of the reactants.
- The surface area of the reactants.
Particle size
The reaction between calcium carbonate and dilute hydrochloric acid is used to prepare CO2. Varying the size of the Calcium Carbonate can make this reaction have a different rate. We could try using one single lump or powder and see which reaction would take longer. The powder would have a higher rate of reaction because it would have a greater surface area and more particles for the acid to collide with.
Concentration
Concentration is a very important factor in rates of reaction. The concentration of a solution can greatly effect a reaction this is because there will be more particles of the reactant to react with, which will decrease the time taken for the reaction. If the concentration of an acid is increased, the rate of reaction will increase because the collision rate would be higher.
Temperature
The higher the temperature the more energy each particle will have which means it will vibrate more, causing the amount of collisions to increase. As the particles collide more than usual at a high temperature then it will have a high chance of reacting, this will increase the rate of reaction.
The Collision Theory
From the kinetic theory of gases, the collision theory of bimolecular reactions in a gas phase was developed. In a reaction between two gaseous substances, A&B, a molecule of A must collide with B for the reaction to proceed but in a concentrated solution there will be a higher percent of reactants which will have no more energy. Not all collisions cause a reaction, only the ones which reach the activation energy of the reaction. This is why I predict that the rate of reaction will increase as the concentration of a solution increases.
Activation Energy
Activation Energy is an amount of Energy needed for a reaction to occur, this amount varies from different elements and types of reaction. This may save energy for industrial use, as they will only supply the exact amount of energy needed and not more.
Evaluation: I feel that after completing my investigation I achieved everything I set out to do. I believe that each of the experiments were completed well because I identified the three factors that affect the rates of reactions like a proposed to do in my aim and plan. The only inaccuracies I can think of when doing the experiments is not achieving the target temperatures of the acids exactly, this would only have a tiny affect on the reliability of my results and the use of averages would have cancelled these out.
If I had the chance to continue the investigation I would try and use more complex equipment and look at the affect of catalysts in a reaction. A catalyst is something that can greatly increase the rate of a reaction and is used a lot in industry to save companies time and money.
All in all the investigation was completed with results to prove my predictions to be correct, and I feel that my results are very accurate and reliable. Every effort was made to keep all of the tests fair and honest and I am very pleased with my outcome.
