The results I got were the following:
These results are not very accurate as instead of the different concentrations of acid being the only variable in the experiment I had a few. The length of the magnesium ribbon and the amount of HCl in each test tube were not exact in each test tube and therefore the results are not similar.
Method:
Step 1: setting up an apparatus of 9 boiling tubes on a test tubes rack.
Step 2: I will measure from the bottom of the meniscus 020cm³ of hydrochloric acid using a measuring cylinder.
Step 3: I will then pour 20cm³ of HCl at concentration of 1M into three boiling tubes. Then I will pour 20cm³ of HCl at concentration of 2M into three boiling tubes. Finally, I will pour 20cm³ of HCl at concentration of 4M into three boiling tubes.
Step 4: I will measure 3cm of magnesium ribbon and cut 9 pieces of the 3cm magnesium ribbon.
Step 5: I will insert one piece of the magnesium ribbon into the one boiling tube with the 1M concentration of HCl and time. I will repeat this twice to get the most accurate answer. Then, I will insert one piece of the magnesium ribbon into the boiling tube with the 2M concentration of HCl and time. Again, I will repeat this twice to get the most accurate answer. Finally, I will insert one piece of the magnesium ribbon into the boiling tubes with the 4M concentration of HCl and time and again I will repeat this twice to get the most accurate answer.
I will record the results each time I do the experiment to see how the rates of reaction vary as the concentration of hydrochloric acid changes.
In order to make my real results a fair test I will make sure that the length of the magnesium ribbon, the amount of HCl, the temperature, the catalysts and the surface areas will be constant so that the concentration of HCl is the only variable in the experiment.
Apparatus:
- Test tube rack
- 9 boiling tubes
- 3cm of Magnesium ribbon
- 20cm³ of 1M hydrochloric acid
- 20cm³ of 2M hydrochloric acid
- 20cm³ of 4M hydrochloric acid
- Safety goggles
- Lab coat
- Stopwatch
- Measuring cylinder
- Ruler
I will have to make sure that the experiment is safe and therefore I will take the following precautions:
- Wear safety goggles to prevent any chemicals getting into my eyes.
- Wear a lab coat so that if a chemical spills on me it will not touch my skin.
- Wash my hands immediately if any chemicals spill on them.
- Calls the teacher immediately if any acid spills.
Obtaining Evidence
After having done the pilot experiment I have done my actual results using what I know I have done wrong when doing the pilot experiment.
The results that I got were as follows:
The independent variable in this experiment is the concentration of HCl and it is what I deliberately change step by step by step. The dependant variable in this experiment is the reaction time and it is what changes depending on the independent variable. All the other variables like the temperature, surface area and the catalysts must be kept constant to make the experiment a fair test.
I will also record my results using a graph in order to show the difference between each experiment:
Analysis
The results that I got for the experiment were as follows; using 1M of hydrochloric acid the magnesium finished reacting at 156.59 seconds during the first experiment, at 157.37 seconds during the second experiment and at 161.56 during the third and final experiment. These results came to an average of 158.51 seconds. Using 2M of hydrochloric acid the magnesium finished reacting at 43.63 seconds during the first experiment, at 45.30 seconds during the second experiment and at 45.53 seconds for the third experiment. These results came to an average of 44.82 seconds. Using 4M concentration of hydrochloric acid the magnesium finished reacting at 23.12 seconds during the first experiment, at 22.57 during the second experiment and at 22.16 during the third experiment. These results came to an average of 22.62 seconds.
The experiment proved that if the concentration is changed the rate of reaction will too. In the experiment I found and confirmed my results to prove my predictions and theory for the effects of the concentration of hydrochloric acid on the rates of reaction of a piece of magnesium ribbon. My predictions were that as concentration increases the rate of reaction will be faster. This means that when doing an experiment using 2M hydrochloric acid and a different one using 1M of hydrochloric the first experiment will be much faster. All the experiments also produced the same gas, hydrogen.
When looking at the graph that I plotted in the previous page I can determine if my predictions were correct. The graph shows that as the concentration of hydrochloric acid increases the magnesium ribbon would react faster. The results agree with the prediction I made earlier because the graph shows exactly what I claimed would happen, which was the higher the concentration the faster the magnesium ribbon would react.
The particles of the reacting substances must collide with each other and, secondly, they need a certain amount of energy to break down the bonds of the particles and form new ones. This energy is called the activation energy or Ea. If a collision between particles can produce sufficient energy (i.e. if they collide fast enough and in the right direction) a reaction will take place. Not all collisions will result in a reaction. Therefore the reaction that took place was as follows:
Magnesium + hydrochloric → magnesium + hydrogen
ribbon acid chloride
Mg(s) + 2HCl(aq) → MgCl2 (aq) +H2 (g)
In conclusion the higher the concentration of hydrochloric acid the faster the magnesium will react, this can be proved using the collision theory. The collision theory states that in order for the particles to react they must collide and the more collision there are the faster the reaction will be. The particles must collide with enough energy to have a reaction. The concentration affects the rates of reaction because when the concentration of the reactant is very high then the amount of particles will increase and so will the amount of collisions so the reaction will be faster.
For the experiment no anomalous results were found, therefore concluding that all experiments were successful with little inaccuracy. The results were accurate in proving my prediction that the effect of a more concentrated solution on the rate of reaction will cause a faster reaction, assuming that the other variables are kept constant.
Evaluation
When evaluating my experiment I could find many ways in which I could improve it to make the results more precise. I could have improved my method by doing some small, but yet critical things to improve the experiment. These would include rinsing out the measuring cylinder when pouring a different concentration of hydrochloric acid just to make sure there is not some of the previous acid left which would not affect the results by much but would still be more accurate. Another way in which I could have improved my experiment would be to measure from the bottom of the meniscus so that I get the exact amount of acid and therefore make the results more accurate. Luckily, I did not have any anomalous results and therefore I can come to a firm conclusion using the information that I got.
To get more accurate results I could improve my experiment by using more efficient equipment that would give me more accurate results. The magnesium could be measured to a more approximate point and the volume of acid could have been better manufactured then using a measuring cylinder. Using a thermometer I could make sure that the room temperature would be kept constant throughout the experiment. I could also make sure that the pressure in the room was also kept constant; I would do this using a monometer. From my own knowledge I know that if magnesium is left out in the air it reacts with the oxygen to form magnesium oxide and therefore some pieces of magnesium ribbon would react faster than others.
