To find out how the rate of a reaction is affected by the concentration of the acid.
Lisa Wilson
Rates of Reaction Coursework
Aim
To find out how the rate of a reaction is affected by the concentration of the acid.
Introduction
Reactions occur faster when the key factors are altered. For a chemical reaction to occur particles must collide together. For any reaction to be successful the collision had to transfer enough energy.
If there is not enough energy transferred the particles will just bounce off one another without the atoms rearranging new substances.
If the temperature of a chemical reaction is increased, energy will be transferred to it. This energy will go back to the particles as kinetic energy. So heating a chemical reaction results in the particles moving faster.
When particles are moving faster they are more likely to collide, and gain more energy. When particles move faster they gain energy, this will lead to collision, which in turn will lead to a reaction.
A catalyst can be used in experiments to speed up or slow down a reaction.
A catalyst often provides a surface where the particles can meet to react. Reactions that occur in this way need less energy transferred to make a collision successfully.
They often allow reactions to work at a lower temperature so fuel is saved.
If the surface area were increased particles would collide more. This is because there are more particles available to react with each other; as they react together they cause a reaction.
If an acid is more concentrated, but the volume is the same, then there are more particles in the same amount of space; this means there is a greater chance of particles colliding and a reaction occurring.
This is the key factor that I will be changing and investigating throughout my experiment.
Example - Circles in a square. Multiply 0's by 2 (more collision)
The diagram indicates that when the particles in the same area are increased the chances of collision are also increased. As the particles have less room to move around.
Prediction
For the experiment I will take a measured amount of magnesium (exactly 1.5 cm each), place it into a test tube with one concentration of acid, and time how long it takes for a reaction to occur ...
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This is the key factor that I will be changing and investigating throughout my experiment.
Example - Circles in a square. Multiply 0's by 2 (more collision)
The diagram indicates that when the particles in the same area are increased the chances of collision are also increased. As the particles have less room to move around.
Prediction
For the experiment I will take a measured amount of magnesium (exactly 1.5 cm each), place it into a test tube with one concentration of acid, and time how long it takes for a reaction to occur (the magnesium to dissolve).
I will then increase the concentration of acid and repeat this process. I will then increase the concentration another 3 times and record how long they each take for a reaction to occur. I predict the more concentrated the concentration (2M of acid) the faster the reaction will occur. Likewise the less concentrated acid will produce a slower reaction. My prediction is linked with the theory, because I predict that the higher the concentration of acid the faster a reaction will occur, because if an acid is more concentrated, but the volume is the same, then there are more particles in the same amount of space; which results in them colliding together. This is stated in my introduction.
Apparatus
For my experiment I will need the following equipment:
* 1 test tube rack
* 1 stop watch
* 5 glass test tubes
* 5 measured amounts of magnesium (all the same size - 1.5cm)
* Hydrochloric acid - 5 different concentrations - 0.4, 0.6, 0.8, 1.0 and 2.0 M
* 1 glass 10cm measuring cylinder
Diagram
Step by step Method
* Take 5 pieces of magnesium - 1.5 cm in length. Place each piece into a test tube.
* Put 5cm of acid, the lowest concentration of acid into the first test tube. And then complete this for the other 4, increasing the concentration each time.
* Using the stopwatch, time how long it takes for each reaction to occur.
* Repeat this method for the other test tubes, increasing the concentration of acid each time. And record each concentration twice, so that the outcome should be two sets of similar results.
* Record all results.
Ensure that safety goggles are worn at all times throughout the experiment. Make sure that all apparatus are sited in a safe place, to avoid spillage/breakage. For this experiment the acid that I will be using is Hydrochloric Acid, it is corrosive acid, so care must be taken, avoiding spillage.
Fair Test
I must ensure my experiment is fair. To do this I must only change on variable, in this case it is the concentration of hydrochloric acid. The other variables must stay the same, for example, the amount of acid and the size of the magnesium.
Throughout the experiment I will take 5 readings and repeat each reading twice so I will end up with two sets of results.
Results
Concentration
of acid
(Molarity)
st results
Time taken for magnesium to dissolve (s)
2nd results
Time taken for magnesium to dissolve (s)
Average
set of results (s)
2.0
45.95
43.00
44.47
.0
23.28
13.60
18.44
0.8
209.34
200.40
204.87
0.6
903.70
849.63
876.66
0.4
2736.26
2616.48
2676.37
Graph - on graph paper.
After analysising my results I found out that both sets were very similar. They suggest that more concentrated acid, the faster the reaction will occur.
This statement supports my prediction. This means that there were more particles in the higher concentration acid, so they collide more to make the reaction faster.
Conclusion
My two sets of results were similar, giving a reasonable average. The high concentration of acid made the reactions faster. This occurred due to the increased amount of particles in the same space. So collision occurred and made the reaction take place faster than the lower concentration of acid.
The particles had less space to move about, unlike before when they had plenty of space, so they are all trying to move about in their own space, which is no longer available to them. This results in collision.
The prediction that, I made seems to be correct, my results support this. My prediction stated that the higher the concentration of acid used, the faster a reaction would occur. This seems to be the case, as the highest concentration reacted a lot faster than the others. When relating my prediction to my graph it is clear to see that they support each other. The graph shows that the high concentration acid, reacts fast, and then as the concentration becomes lower the reaction is slower. This is showed by the curve on the graph.
Concentration of Acid (m)
Average Time Taken (s)
0.4
880
0.6
400
0.8
200
.0
20
.2
00
.4
80
.6
60
.8
40
2.0
40
From the table and the graph, it is clear to see that there is no obvious pattern occurring within my results. The time taken varies a lot for the different concentrations.
Evaluation
Overall I think my experiment did not go too bad. Everything went to plan and my results turned out ok. My experiment went well but I could in the future make sure that my results are as accurate as possible, this could be achieved by making sure the measurements of the acids and magnesium are all measured accurately, the same. By making sure that my measurements are all identical, with no measurement different to another.
On my graph not all of the results are on the curve, this could be due to the differences in the concentration of the acids, and how the concentration is related to the speed of the reactions. If I had to do the experiment again I would have changed the way I measured out my magnesium, as I think the size of the magnesium was slightly too large, as some of my tests took a while for the reaction to occur. So by using slightly smaller pieces of magnesium, the reactions would occur slightly faster, and they should still bring a similar outcome. If both, my results and the results from the new experiment turned out similar, with no pattern. It would suggest accuracy in both experiments.
My evidence was reliable because I kept all the amounts of acid and magnesium as accurate as I could. And I tried to keep them all the same size. Both sets of results were similar, so this suggests reliability and accuracy.
If I had more time I would have also investigated how reactions can be affected by a change in temperature.
