The effect of concentration on the rate of reaction.
The effect of concentration on the rate of reaction
Aim: The purpose of this experiment is to find out if and how the concentration of a solution affects the speed of a chemical reaction.
The reaction that I am going to study is magnesium and hydrochloric acid.
Magnesium + Hydrochoric acid --> Magnesium chloride + hydrogen
Mg(s) + 2HCL (aq) --> MgCl2 (aq) + H2 (g)
Prediction: As we increase the concentration, the rate of reaction will also increases. The collision theory explains why the concentration affects the rate of a reaction. As the concentration of the acid increase, there are more acid particles in the same volume. Therefore, there is a great chance of acid particles colliding and reacting, with magnesium particles. So the rate of reaction will increase.
Apparatus:
* 20 cm of magnesium ribbon
* scissors for cutting the magnesium ribbon
* Emery paper to wipe off the deposit of magnesium oxide formed on the surface of the magnesium ribbon.
* 2M of diluted hydrochloric acid
* distilled water to dilute the acid
* a stop watch to see how long it takes for the rate of reaction
* 20 ml cylinders- to measure the amount of distilled water and acid.
* Test tube racks- to hold the test tubes
* 4 test tubes
* ruler- to measure the length of the magnesium ribbon
* pipettes
Fair testing: Variable that I will control:
Magnesium ribbon- I have to make sure that each one of them is exactly 1.5 cm long, so each of them will have the same surface area exposed to the HCL. I will have to sand out every bits of magnesium oxide deposit on the ribbon, so the layer of oxide wouldn't affect the rate of reaction.
Temperature- I have to make sure that I have to perform my experiment in a lab, so it is room temperature- 23 degrees. Temperature can affect the rate of reaction, if the temperature increase, it makes the particles collide more often in a certain time. The temperature should be roughly the same.
Variable that I will change:
The concentration of HCL- I am trying to find out how the effect of concentration affect the rate of reaction, so I have to change the concentration of the acid in order to investigate the aim. The collision theory ...
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Temperature- I have to make sure that I have to perform my experiment in a lab, so it is room temperature- 23 degrees. Temperature can affect the rate of reaction, if the temperature increase, it makes the particles collide more often in a certain time. The temperature should be roughly the same.
Variable that I will change:
The concentration of HCL- I am trying to find out how the effect of concentration affect the rate of reaction, so I have to change the concentration of the acid in order to investigate the aim. The collision theory explains why the concentration affects the rate of a reaction. As the concentration of the acid increase, there are more acid particles in the same volume. Therefore, there is a great chance of acid particles colliding and reacting, with magnesium particles.
The amount of distilled water- the amount of distilled water is to dilute the concentration of acid in order to change the concentration of the acid.
Method:
. Use emery paper to sand off the layer of oxide on the magnesium ribbon.
2. Use a ruler and a scissors, divide the 20 cm of magnesium ribbon into 12 pieces, 1.5 cm each. (there will be some magnesium ribbon left over)
3. Use the measuring cylinder, measure 10 ml of 2M HCL, then pour it into a test tube.
4. Use the measuring cylinder, measure 7.5 ml of 2M HCL, then another 2.5 ml of distilled water (to dilute the acid), pour them into another test tube. This will make the concentration of 1.5 M of HCL.
5. Use the measuring cylinder, measure 5 ml of 2M HCL, then 5 ml of distilled water (to dilute the acid), pour them into another test tube. This makes concentration of 1M of HCL.
6. Use the measuring cylinder, measure 2.5 of 2M HCL, then another 7.5 of distilled water (to dilute the acid). Pour them into another test tube. This makes the concentration of 0.5 M of HCL.
7. At the same time, put 4 pieces of 1.5 cm of magnesium ribbon, 1 each into each test tube.
8. Start the stopwatch straight away.
9. Measure the time taken for the magnesium to disappear in the solution, and it stopped bubbling and giving off hydrogen gas.
0. Record the result in a table.
1. Pour away all the solution in the test tubes and wash them.
2. Repeat steps 3-10 for 3 times, so we can obtain an average to ensure the accuracy of this experiment.
Time taken for the magnesium ribbon to disappear (s) rounded up to nearest seconds.
Concentration of HCL (M)
st time (s)
2nd time (s)
3rd time (s)
Average time (s)
2
5
8
9
7
.5
37
52
40
43
10
80
90
93
0.5
330
380
420
378
Conclusion
The graph agrees with my prediction. According to the set of results obtained, it shows that the more concentrated acid had a faster rate of reaction than the less concentrated acid. The line of best fit is a steep line. As the concentration increase, the rate of reaction also increases. The closer the ions are closer in a concentrated solution, the more often the ions collide. Therefore higher the chance of a reaction between the magnesium and the hydrochloric acid.
Evaluation
There are parts in my experiment that allowed me to get good results. I did each experiment three times so I would be able to calculate averages to get more accurate results. I recorded the results in seconds instead of minutes in order to obtain more precise results. I used a stop clock instead of a 24-hour clock so I could look at the milliseconds and round it up to the nearest second, which made the results more exact.
The experiment supported my prediction. The more concentrated the acid is, the faster the rate of reaction. In a higher concentration there are more acid particles to react with the magnesium ribbon and therefore it is eaten away faster.
The experiment was carried out in the lab, so the temperature should be roughly the same. I used magnesium ribbon for the testing to ensure that the property of the chemical wouldn't affect the results. I made sure that all the magnesium ribbons were 1.5 cm long, so they had the same surface area, therefore it is a fair testing. I used emery paper to sand off all the deposit of magnesium oxide on the surface, so the acid would not have to react with the oxide first.
However, the results are not totally reliable. There are a few rogue results highlighted in my table and on the graph. This experiment cannot produce very accurate results, due to numbers of factors. Firstly bubbles of H2 were given off when the reaction took place, which might stay around the magnesium, so it could reduces the surface area of the magnesium and so the acid cannot react properly with the magnesium. This is hard to control and it could affect the accuracy of the result. In theory, the concentration of the acid should be accurate, but due to human errors, it was not, because the concentrations of the acid were mixed by hands. It was very hard to measure out the exact number of millilitres for the acid even though I used a pipette. Every time I washed a test tube or a measuring cylinder, I did not dry it before using it. This may have affected the rate of reaction, as water would dilute the acid. Also, I stopped the stopwatch when I saw the magnesium ribbon disappear, however in reality, the reaction might not have finished, so it leads to inaccurate results.
Modification
We could have controlled factors in the investigation better such as stirring of the mixed solution because if this is not done properly it can lead to incorrect results.
To improve my results, I could dry the test tubes and the measuring cylinder after they are washed to prevent diluted acids. The size and weight of the magnesium would have affected the rate of reaction. The experiment could be improved by measuring, adjusting and weighing the magnesium ribbons so they all are the same size and weight instead of just cutting them to 1.5 cm long.
In order to improve the accuracy of my results, I should not use those concentration of acids mixed by hands, because human errors can affect the concentration of the acid. I should also stir the solution to make sure that the concentration of the acid is spread evenly in the test tube to ensure accurate results.
