MAGNESIUM!
Magnesium is a very reactive metal, even more so when it reacts with an acid. Magnesium is used for sacrificial protection, so that the Magnesium is eroded before the steel hull of the ships. In this experiment, the Magnesium should react well with the Hydrochloric Acid, but less as the Hydrochloric Acid is diluted.
HYDROCHLORIC ACID!
Acids are very corrosive and Hydrochloric Acid is one of the more corrosive acids. In this experiment I am reacting a very reactive metal, (Magnesium) and very corrosive acid (Hydrochloric Acid).
VARIABLES!
There are a few variables that will affect the results. They are the following:
Concentration of Hydrochloric Acid: As the Hydrochloric Acid is diluted, the concentration will be less, and therefore the rate of reaction will be slower. The Hydrochloric Acid is the dependent variable because it will vary, and the time taken for the rate of reaction to take place will change, depending on the amount of Hydrochloric Acid.
Magnesium Ribbon: The Magnesium Ribbon will stay at a length of 2cm. It is kept at a length of 2cm so that the experiment is fair and accurate.
Room Temperature: The room temperature will stay the same because if the room temperature increases or decreases the rate of the reaction will increases or decrease respectively due to the fact that a hotter temperature will result in more energy in the particles and therefore more collisions, therefore increased rate of reaction. Decreases in the temperature would do the opposite in the fact that the particles would have less energy to collide and therefore a slower rate of reaction.
APPARATUS!
- 2CM Strip of Magnesium.
- Hydrochloric Acid
- Water
- Two test tubes
- Safety Goggles
- Stop Watch.
METHOD!
To get the amount of magnesium and the amount of hydrochloric acid to use in the
situation, we have to use an excess of acid so that all of the magnesium disappears.
An equation for the reaction:
Magnesium + Hydrochloric Acid = Magnesium Chloride + Hydrogen
Mg(s) + 2HCL(aq)>Mgcl2 (aq) + H2 (g)
When I did the experiment, I diluted the acid solution using water, as I did this the
concentration of the acid decreased. We put the acid (1 mole) into the 10ml test tube and
then poured the solution into the beaker with the Magnesium Ribbon in it (2cm long) and then I measured the time taken for the magnesium ribbon to disappear, using the stop clock. Next, I diluted the acid by placing 8ml of acid (0.8 mole) and 2ml of water into the test tube and then poured it into the beaker with the magnesium and measured the time taken for the magnesium ribbon to disappear using the stop clock. Then 6ml of acid (0.6 mole) and 4ml of water solution on the magnesium, I then measured time taken for magnesium to disappear using stop clock. Then 4ml of acid (0.4 mole) and 6ml of acid, repeated as above. Then 2ml of acid (0.2 mole) and 8ml of water, repeated as above. I repeated the experiment twice to get a fair test by proving that all results are accurate. I put the results in table as soon I calculated each result.
FAIR TEST!
To ensure that the test is fair I must make sure that the length of the Magnesium Ribbon stays at the same length of 2cm because it is the only element of the experiment that must not be changed. If it is changed then the experiment will be inaccurate and not fair. I must measure the correct proportions of Hydrochloric Acid and Water, because if I add too much Hydrochloric Acid and not enough Water, then the rate of reaction will be too fast, and if I have too little Hydrochloric Acid and too much Water, then the rate of reaction will be too slow. I will try to make sure that the Water and the Hydrochloric Acid are both added at the same time, or near enough so that the test is fair, and so that the components have the same amount of time to react with the Magnesium Ribbon. I can’t control the room temperature but I hope that it will stay at the same temperature. In order for the test to be fair, I must also make sure that I stop the clock at exactly the right moment, if I am seconds early or late, then the results will not be fair at all.
PRELIMENARY RESULTS!
This is the preliminary table of results:
As the results show, as the concentration of the Hydrochloric Acid is diluted, the slower the rates of reaction are. I predicted that the rates of reaction would decrease and they have, as looking at the average results, at a concentration of 10cm3 Hydrochloric Acid, the rate of reaction is timed at 15.54 seconds, whilst at a concentration of 4cm3 the rate of reaction is 218.12 seconds, so for the preliminary results, my prediction was correct.
ANALYSIS!
This is the final table of results:
The above table is the final table of results, and the results show that part of my prediction was correct. I correctly predicted that as the concentration of the Hydrochloric Acid decreased, the rate of reaction would increase. The first record states that it took 11.02 seconds for the Magnesium Ribbon to dissolve in a solution that had 10cm3 of Hydrochloric Acid. At a volume of 8cm3 the rate of reaction increases to 23.00 seconds, which is an increase of 11.98 seconds. This proves that my prediction was correct, however I predicted that as the Concentration of Hydrochloric Acid decreases, the rate of reaction would double so if the time taken at 8cm3 is 23.00 seconds, at 4cm3 of Hydrochloric acid, the rate of reaction should be 46.00 seconds. However the recorded result is 125.68 seconds, so it has more than doubled.
The second set of results (time 2) has the same trend as the first set of results as the rate of reaction increases as the volume of Hydrochloric Acid decreases, as the first record, when the Hydrochloric Acid has a volume of 10cm3, the rate of the reaction is 10.05 seconds. When the Hydrochloric Acid has a volume of 8cm3, the rate of the reaction is 24.20 seconds. Again my prediction is correct, but as I said the rate of reaction would double, my results do not agree, as when the Hydrochloric Acid has a volume of 4cm3, the ate of reaction is 131.32 seconds, if the rate of reaction doubles, then the next result should be 262.64 seconds. Instead, the result is 197.28. That’s 65.36 seconds behind the predicted result.
The average results show the same trend as the Time 1 and Time 2 records, in the fact that as the volume of Hydrochloric Acid decreases the rate of reaction increases. At a volume of 10cm3, the average rate of reaction is 16.04, and at a volume of 6cm3, the rate of reaction has increased to 93.97, which is a total increase of 77.93 seconds. However, yet again the results do not double as I wrongly predicted. When the volume of the Hydrochloric Acid is at 8cm3, the rate of reaction is 35.10 seconds, therefore at a volume of 4cm3, the results should be 70.2 seconds, yet the actual result is 191.34, which is a total increase of 121.14 seconds.
GRAPH 1 OF RESULTS.
This graph of results shows that as the concentration decreases the rate of reaction increases.
In every record, they can be explained using the information in the Background Knowledge. I stated in the Background Knowledge that as more water is added to the Hydrochloric Acid, the rate of reaction would increase because it would take longer for the Hydrochloric Acid particles to collide with the Magnesium particles as the Hydrochloric Acid molecules would now have to bounce off the Hydrogen and Oxygen molecules before the Hydrochloric Acid molecules hit the Magnesium molecules and also there would be less energy in the Hydrochloric Acid particles, so it would take more time for the particles to react and all the Magnesium to be dissolved. Basically, the more dilute the concentration the Hydrochloric Acid is, the rate of reaction increases.
CONCLUSION!
Using the evidence that I have, which is the table of results and the graph, I believe that as the concentration of Hydrochloric Acid was diluted, the rates of reactions increased due to the fact that there was more molecules in the solution, making it harder for the Hydrochloric Acid molecules to react with the Magnesium molecules, because the added water molecules were similar to extra cars joining a traffic jam, it would take even longer for other cars to reach the destination. In scientific terms, the ions of the Hydrochloric Acid would be further away from the Magnesium ions, meaning less successful collision and an increased rate of reaction. In the reaction, when the Hydrochloric Acid hit the Magnesium Ribbon, it fizzed and produced many bubbles that were silver (which is one of Magnesium’s physical properties, that it is a silvery
white metallic element), the activation energy of a particle gets higher with heat, the
molecules which have to have the activation energy are those molecules that are moving, which in my experiment, was the Hydrochloric Acid molecules which had to have the activation energy because they were the molecules that were moving and bombarding the Magnesium particles to produce Magnesium Chloride. The graph for1/time showed a positive trend.
My prediction was correct, as the figures show in the analysis.
EVALUATION!
I believe that the experiment was well done. I was pleased to see that my prediction backed up by the Background Knowledge was correct. I started out the experiment wanting to find out if the concentration of Hydrochloric Acid was diluted would it effect the reaction with the Magnesium and would the effect be negative (increased rate of reaction) or positive (decreased rate of reaction).
However the experiment was not perfect, and the results do show that. I obtained two anomalous results, which was when the concentration of Hydrochloric Acid to water was 6:4, when the average time was 93.97, and the result before that was 35.10. Now that result is more than double, because double 35.10 would be 70.2, yet the result I obtained was 23.77 seconds on top of the 70.2 seconds that I expected that I would get. The other anomalous result I obtained was the final result, when the concentration of Hydrochloric Acid to Water was 2:8, and the average result was 300.98. The result before that was 191.34. Now doubling 191.34 is 382.68 seconds, but I obtained 300.98 seconds, a full 817 seconds slower than what I initially thought I’d get but on the graph, the distance between the fourth and fifth result was the biggest increase on the graph as the gradient is steeper.
I believe that there are a few reasons as to why I obtained the anomalous results. The first reason is that I added too much Water, when the concentration of the Hydrochloric Acid to water was 6:4, and when the concentration was 2:8 in favour of the Water, I added too little and possibly too much Hydrochloric Acid, so the combination of the two miscalculations would result in the rate of reaction being faster than I predicted. Another reason is that I cut the length of the Magnesium too big at a concentration of 6:4 and too small at a concentration of 2:8. Another explanation is that there could have been a change in temperature. Although it is not a very strong explanation, it is still a theory. And my last theory as to why I obtained the anomalous results is that when the reaction takes place bubbles of H2 are given off which might stay around the Magnesium which therefore reduces the surface area of the Magnesium and so the Hydrochloric Acid cannot react properly so this effects the results.
If I were to do the experiment again, I would like to have more time so I could get more results and get a bigger variety of knowledge from the results. If I was to repeat the experiment my second aim, would be to eradicate any anomalous results, so if I added too much or too little Hydrochloric Acid or too much or too little Water, I would have all the measurements poured out before in separate containers. That would rule the risk out of me obtaining anomalous results due to too much or too little of a substance. To eradicate the risk of the Magnesium Ribbon being too big or small, if I was to do five experiments, I would get 5 pieces of Magnesium Ribbon and put the pieces one under the other, measure the Magnesium Ribbon on top, and then cut down the five Ribbons, therefore, even if the Magnesium Ribbons have been cut too small or big, they would all be exactly the same size.
