Pilot Apparatus
- 2 100ml Beakers
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1 25cm3 measuring cylinder
- 1 Stopwatch
- 2m Hydrochloric acid
- Safety Goggles
- Distilled water
Pilot Method
- Collect all equipment
Cut 5, 1cm stripes of magnesium ribbon
Clean them thoroughly using sand paper
Measure 25cm3 of 2M Hydrochloric acid in a measuring cylinder
Poor the acid in to a beaker
Put a piece of magnesium ribbon in to the acid, at the same time starting the stopwatch
Stop the stopwatch.
Write down the results in seconds.
Diagram
Pilot Results
Pilot Analysis
I think that my pilot went quite well, because I have managed to get three results that show me that rate is affected by concentration. I decided to modify my pilot to make my results more accurate, I have decided to stir the solution, with a glass rod, so that the weaker concentrations do not take as long to finish reacting, because I found that the concentrations were taking far to long, and I will cut the magnesium up in to smaller pieces so there is more surface area for the reaction to take place. I will still use the same concentrations as before 2M, 1.6M, 1.2M, 0.8M and 0.4M. In my pilot I found that the main thing that did not go well was the length of time that it took for the lower concentrations to finish reacting, so I have decided that I will stir the reaction and to cut the magnesium in to three pieces. Apart from that the rest of my experiment went well and I have now modified my pilot.
Key Variables
To make a fair test I must only change one variable at a time, the one I am investigating. I must keep all the other variables the same.
Dependant – The dependant variable is the thing that you are measuring, in this experiment it is the time taken for a 1cm stripe of magnesium to disappear.
Independent – The independent variable is the thing that you are going to investigate, in this experiment I am investigating what effect concentration has on the rate of a reaction, I am going to do this by using different concentrations of hydrochloric acid from 2M to 0.4Mwith an interval of 0.4.
Controlled - To make a fair test I must only change one variable at a time, the one I am investigating. I must keep all the other variables the same.
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Temperature – I will not be able to control this variable because this reaction is exothermic. I will not be able to control this variable because it is impossible for me to control. I need to control this factor because temperature does also increase rate of reaction.
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Length Of Ribbon – I will have to keep the length of magnesium ribbon the same length because otherwise the experiment will take longer, if the ribbon is longer, or less time, if the ribbon is shorter. I will I need to keep the same volume of acid whatever the concentration otherwise I will
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Same Volume Of Acid - I need to keep the same volume of acid whatever the concentration otherwise I will increase or decrease the rate because there will be more particles of acid for the magnesium to collide with.
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Stirring – I will keep this variable the same by stirring all the concentrations because then I will be decreasing the time taken for the magnesium ribbon to disappear. I will also stir the reaction in the same method, by holding the magnesium to the bottom of the beaker; otherwise the reaction may be speeded up or slowed down, this way I know it will be all the same. This variable may also affect the surface area.
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Same Apparatus – I have to use the same apparatus because otherwise I could pick a different size beaker, which could make it look like there was more acid than if it was in a larger beaker. I will keep this variable by using the same apparatus.
Prediction
I predict that when concentration increases so will the rate of reaction. This is because in a solution with a stronger molarity there is more surplus energy to break bonds therefore the magnesium will disappear, in less time than if it is in a solution with a weaker concentration, this has less available energy to break bonds. In a more concentrated solution the particles of the solution are closer together because there are more particles in the same amount of solution and are therefore more likely to make successful collisions. However in a solution with a lower molarity the rate of a reaction, or time it takes for the Magnesium to disappear will be slower because the particles in the solution are further apart because there are less of them because there is more water in the acid. I have seen, by using my pilot, that what I have said in my prediction is true. But if I don’t I will know that my readings were not accurate enough. I am also going to draw a graph of time taken against concentration:
Time Taken (S)
Concentration
In my 1/time graph I will expect to see a straight line because the rate of a reaction is directly proportional to the concentration:
Rate
Concentration
Rate of Reaction = Amount of Substance
Time (S)
The Amount Of Magnesium Chloride Produced = A Constant Amount
This is because there is a fixed amount of magnesium and Hydrochloric acid
I predict that the rate at 2M will be twice as fast than at 1M because as concentration doubles so does rate. I know this will happen because the collision theory states that when reactions occur reactant particles have to collide with sufficient energy, the activation energy.
Diagram
Apparatus
- 2 100ml Beakers
-
1 25cm3 measuring cylinder
- 1 Stopwatch
- 2m Hydrochloric acid
- Safety Goggles
- Glass rod
- Distilled water
Method
- Collect all equipment
Cut 5, 1cm stripes of magnesium ribbon
Clean them thoroughly using sand paper
- Cut the ribbon in to 3 smaller pieces as this creates surface area
Measure 25cm3 of 2M Hydrochloric acid in a measuring cylinder
Poor the acid in to a beaker
Put a piece of magnesium ribbon in to the acid, at the same time starting the stopwatch.
- While the reaction is taking place stir the mixture
Stop the stopwatch.
- Write down the results in seconds.
- Repeat the experiment 3 times and more if the results are not close enough, within 10% of each other.
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Repeat the same process except with a different concentration of acid, to dilute the acid add a smaller amount of acid and add water to make the volume up to 25cm3.
Analysis
In this experiment I had some anomalous results, I will show these by putting a purple background on them. I have decided that I will make a result anomalous if they more that 10% away from the others, in either direction, I found that I had lots of these, and therefore had to repeat my experiment more than before, this was because there were so many errors of the method. When I calculated my average I did not include my anomalous results, this was because they were inaccurate results and therefore made my average wrong. Anomalous results are results that are more than 10% away from the other results; in higher concentrations the results need to be closer together because the time is much less whereas for higher concentrations the results can be further apart.
In my graph (Rate against concentration) I found that I had a straight line that did not go through the origin or 2 points. I think that this was because my method had lots of areas where errors could appear. For the graph which showed Average time against concentration was a curve which I had expected, it was also in the direction that I expected, although some of my results were more or less than double, which is what I had predicted in my prediction. This is because when concentration increases time decreases, I know this because the collision theory sates that a chemical reaction can only happen when particles collide with sufficient energy. The minimum energy for a successful collision is called the activation energy. The more frequent the faster the reaction. Although both my graphs are not totally what I expected I can see which points are wrong.
In my graph (rate against concentration) most of my results were close to double the previous:
At 1M rate is 2.
At 1.4M rate is 4, which is exactly double the previous reading.
At 1.8M rate is 6, which is again exactly double.
This shows that there is a doubling relationship between each point. In my experiment there were many limiting factors that could have changed my results, such as: - the molarity of the HCL (before dilution), whether the water was distilled or not, how well the magnesium ribbon was cleaned or the equipment I used
Evaluation
In my experiment I found that I could not say that any result was not anomalous with in 10 seconds, although this would have been correct for the first readings I would have had to repeat the lower concentrations lots because 10 seconds is a very short time in 300seconds. So I decided to say 10% because this is a wider band a low concentrations and close for high concentrations. In my results there were quite a few result that I did not expect. Some were much higher than the rest and some were much lower. I found that I had to repeat many of my results. I think that these errors were due to the fact that this experiment has many errors in it and there is not much anyone can do to eradicate them. On my graphs there was no other possible line or trend that I could have drawn using my results and the line I have draw already uses the results to the greatest advantage. In my experiment I had to try and keep as many of the variables the same as I possibly could.
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Temperature – I could not control this variable what so ever, because the reaction is exothermic and there was no chance of me doing anything to prevent it occurring, the reason that temperature would effect my results is because temperature speeds up the rate of reaction.
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Length of Ribbon – I was able to keep this variable the same all the way through because I measured every piece of magnesium with the same ruler, then I cleaned in the same way each time.
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Same Volume Of Acid – I used the same volume all the way through me experiment, to measure the amount I used a measuring cylinder, this was the most accurate piece of equipment that was sensible to use.
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Stirring – In my experiment I stirred all of them to get the results in the same way so I have definitely kept this variable the same.
Same Apparatus – I could not use the same apparatus all the time because there was not enough for everyone to have there own, so I could have some error there, although I did clean the it all before I used and I used the same sized beaker for my experiment.
The largest area where error did occur in my experiment is that the experiment was exothermic (created heat), other areas where error could have occurred if I did not take, as much time was the apparatus and the length of the ribbon. All of these errors made my test very inaccurate so the results I have collected are almost the best I could have collected in the circumstances. I could reduce the amount of errors by weighing magnesium granules so that I could weigh them more easily. For this experiment I could also use an inverted burette in water:
This would improve my investigation because you can take much more accurate Burette readings, but it would mean collecting time amount of gas lost and concentration which is quite hard to organise.