These factors will affect the rate of reaction. This is because of the collision theory. The collision theory shows us that it is necessary for the reacting particles to collide with each other particles. This is so there is enough energy to form or break bonds between the particles. If however, the particles do not have enough energy then the particles will bounce back not causing a collision. The minimum amount of energy needed for a collision to take place between the particles is called the activation energy. Source - (GCSE chemistry revision guide, by Ian Lee)
The Maxwell Boltzmann curve is a graph that predicts the probability that the different particles will collide with each other at different temperatures. On the graph shown below the dark shaded area shows the particles that have enough energy to collide with each other. The very light shaded area is the particles that do not have enough energy to collide because they do not have enough energy. The line on the graph showing the activation energy is the minimum amount of energy that is needed for the particles to collide. This Maxwell Boltzmann curve can be related to the reaction between magnesium and hydrochloric acid because the graph shows us how much energy is needed for the particles to make and break new bonds.
The equation K[a] shows the number of variables that are acting on the reaction between magnesium and hydrochloric acid.
K = rate constant
A = the reactant
M = the order of the reaction
The rate constant is the amount of hydrochloric acid this is 25 ml. The reactant used is the concentration of the hydrochloric acid. The order of reaction is calculated by the number of variables that the reaction uses. In this, case the order of reaction is one. This is because the only variable in the reaction is concentration.
Apparatus
- Hydrochloric acid (0.1 molar, 0.5 molar, 1 molar, 3 molar, 2 molar, 5 molar)
- Measuring cylinder - to measure the amount of hydrogen gas given off
- Water - used in the experiment
- Magnesium strips - Used to react with the hydrochloric acid
- Stop watch - to measure the time of how long the reaction takes place
- Water basin - to put the water in
- Beaker - to put the solution in
Fair Test
-To make this a fair test I have to take a number of precautions. The first precaution I will take will be to keep the temperature of the hydrochloric acid the same. This will ensure that the rate of reaction is not increased by the temperature.
- I will also keep the volume of hydrochloric acid the same. This will make the test fair because then the volume of the acid will not affect the rate of reaction.
- I will also try to keep the surface area of the magnesium the same. This will make the test fair because it will then not speed up the rate of reaction in the experiment.
Safety
- To ensure safety I will also check that the tube containing the hydrogen gas will contain no leaks. This is so it does not make the test unfair if the hydrogen gas leaks.
- Wear safety goggles so that if the reaction spits you definitely will not get acid in your eyes
- Hold the acid bottle by the label so that if the acid spills down the side of the bottle it wont be the label side it will always be the other side
- Wipe it up immediately if the corrosive acid spills
Method
1) To start the experiment we will gather all the equipment that is needed in the experiment. We will then cut a 4 cm piece of magnesium ribbon to be used in the experiment.
2) We will then measure the 50 cm of 1 mol dm hydrochloric acid. I will then measure this using the measuring cylinder. I will then pour the hydrochloric acid in to the flask.
3) I will then arrange the equipment in the way shown in the diagram of the experiment. When I have set the equipment appropriately, I will add the 3 cm piece of magnesium to the flask. The magnesium strip should now start to react rigorously with the hydrochloric acid. I will then replace the bung as quick as possible to avoid the loss of hydrogen gas. At this point I will start the stopwatch.
4) When the magnesium has totally stopped reacting, I will stop the stopwatch. I will then record the time and the volume of hydrogen gas given off in the reaction.
5) I will then repeat the experiment using different molars of hydrochloric acid. The different molars I shall use are 0.1, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0. For each molar, I will the experiment 3 times.
6) After completing the experiment, I will clear up the work area. I will also wash up the dirty glass area and wash up the water basin.
Results
To work out the rate of reaction, I will use the following equation -
Rate of Reaction = Average Volume
Average Time
The rates of reactions are shown on the following page -
Rates of Reaction results
0.1 Concentration
Rate of Reaction - 3427.3 = 0.0067
23.4
0.5 Concentration
Rate of Reaction - 532.3 = 0.0823
39.5
1.0 Concentration
Rate of Reaction - 70.6 = 0.7875
41.6
2.0 Concentration
Rate of Reaction - 23.22= 3.5223
57.2
3.0 Concentration
Rate of Reaction - 11.81 = 6.1102
68.3
4.0 Concentration
Rate of Reaction - 7.53 = 8.5684
72.9
5.0 Concentration
Rate of Reaction - 3.84 = 9.958
83.5
Analysis
I conclude that my 1st prediction was correct as the higher the concentration of hydrochloric acid, the faster the rate of magnesium reacting. This is shown in the line graph (fig 1).
I also conclude that the 2nd prediction was also correct because when the concentration of the hydrochloric acid was high, a higher rate of hydrogen was given out. This is proved in (Fig 2).
The 3rd prediction was also correct because when there was a high concentration of hydrochloric acid, there was a higher rate of reaction. This was shown in the graph (Fig 3).
However, my 4th prediction was not correct. This was unexpected because I thought when the concentration was doubled I thought that the rate of reaction would also double. However, this was not true, because when the concentration was at 1.0 and the concentration doubled the result should have been roughly 1.56, this was not true because the actual rate of reaction was 3.5223. This was also proved when I looked at 3.0 molar results. When the concentration was doubled to 4.0, the rate of reaction did not double. The result should have been calculated at 12.22, this was not true as the actual rate of reaction was 8.5684.
The general trend on the line graph (Fig 3) shows that as the concentration of the hydrochloric acid increased the rate of reaction also increased. This was because as the concentration increased the number of particles colliding with each other also increased. Concentration molar 5.0 was the fastest concentration because the rate at which the magnesium dissolved was quickest for the concentration.
The concentration with molar 5.0 had the highest rate of reaction. This meant that the 0.1 concentration had the lowest rate of reaction.
The reaction between hydrochloric acid magnesium is an exothermic reaction, which means that this reaction gives out heat. As this reaction gives off heat, this process will affect the rate of reaction. This should affect the rate of reaction graph (Fig 3) but I found out that my rate of reaction graph was unaffected.
The conclusion I have made is based on the collision theory. The collision theory shows us that when there is enough energy in the particle the reactant can break or form bonds. In this case, the concentration increased the speed at which the particles collide. This means that as the concentration increased the speed of particles colliding increased because the particles had more energy.
Evaluation
To improve this reaction between magnesium and hydrochloric acid I could have used more reliable equipment that measured more accurately. This would have improved the accuracy of the results.
We could have also used precise measuring equipment to measure the hydrochloric acid and the magnesium. This would have given us results that are more accurate.
To improve the accuracy of the experiment we could have repeated the investigation more times than 3 times. This would have given us results that are more accurate.
To further improve the investigation we could have used different rates of concentration. This would have given a wider range of results.
To enhance the experiment further we should keep the room temperature constant. This would help the accuracy of the experiment because if the temperature were constant the rate of reaction would not be affected by the temperature.
To improve our investigation in the future we could have used a more accurate stopwatch or used a better device of checking if the magnesium had fully dissolved.
To improve our investigation in the future we could have used a logiests data logger. This would have helped us to achieve more accurate results in the investigation.
In my investigation, there were a few abnormal results when compared to the overall average. For the 0.1 concentration the result was 3325.8, however the average time for 0.1 concentration was 3427.3. This means that the result is abnormal because the reading is not equal to the average time.
For the 0.5 concentration the result was 510.4, however the average time for the 0.5 concentration was 532.3. This means that the result is abnormal because the findings are not equal to the average time.
For the 1.0 concentration the result was 79.2, however the average time for 1.0 concentration was 70.69. This means that the result is abnormal because the reading is not equal to the average time.
For the 3.0 concentration the result was 12.5, however the average time for 3.0 concentration was 11.81. This means that the result is abnormal because the findings are not equal to the average time.
I think that the abnormal results were caused by either wrong measurements of hydrochloric acid or the inability to view when the magnesium strip had dissolved. This would mean that the results would be higher or lower than the average time result.
When we completed our experiment, we could have investigated further by experimenting with different concentrations of hydrochloric acid or different lengths of magnesium. This would have given us a wider range of results.
Bibliography
Text Books
GCSE Chemistry Science– Written by Alain Anderton, Second Edition
GCSE Bitesize - Science Chemistry revision guide, written by David Smith
OCR Chemistry Text book - Written by David Lee
People
Deepak Tailor - The designer of this brill coursework
Shila Tailor - this person helped me with this investigation.
Mrs Kemp - my Science, Biology teacher
Mrs Zanab - this teacher helped me with this investigation
Electronic
Electronic services also helped me with my report. This included the use of the internet. The websites used to get the information included: -
www.Sciencerevision.co.uk
www.Bitsize.com/Chemistry
www.ChemistryInfo.co.uk
www.OCR-Chemistry.co.uk
In this investigation, I also used e-mail to help with my investigation.
And of course www.corseworkinfo.co.uk
Deepak Tailor
Beal High School
