Dependent Variable: Gas produced as a result of the reaction measure over 10 second time period.
Controlled: Temperature, Amount of Magnesium (and also surface area), Hydrochloric acid (1mol dm-3), Sulphuric acid (1mol dm-3), Hydrochloric acid (1mol dm-3).
Apparatus and Chemicals:
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Conical flask (100 cm3)
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Rubber bung and delivery tube to connect conical flask to 100cm3 gas syringe
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Measuring cylinders (100 cm3)
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Clamp stand, boss and stand
- Stop watch
- Graph paper
- Magnesium ribbon, cut into 3cm pieces and coiled
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Hydrochloric acid, 1 mol dm-3
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Hydrochloric acid, 2 mol dm-3
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Sulphuric acid, 1 mol dm-3
Procedure
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Measure 50 cm3 of 1 mol dm-3 hydrochloric acid using a measuring cylinder. Pour the acid into the 100 cm3 conical flask.
- Set up apparatus as shown in the diagram.
- When you are ready, add a 3 cm strip of magnesium ribbon to the flask, put the bung back into the flask as quickly and you can and start the stop watch.
- Record the volume of hydrogen gas given off at suitable intervals (e.g. 10 seconds). Continue timing until no more gas appears to be given off.
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Clean the conical flask and repeat with 50 cm3 of 2 mol dm-3 Hydrochloric acid.
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Clean the conical flask and repeat with 50 cm3 of 1 mol dm-3 sulphuric acid.
Results
Hydrochloric acid (1 mol dm-3)
Hydrochloric acid (2 mol dm-3)
Sulphuric acid (1 mol dm-3)
Analysis:
Initial rate of reaction of magnesium and the rate halfway through the experiment:
Hydrochloric acid (1 mol dm-3)
Trial 1
10 cm3/10 sec = 1.1cm3/sec
55 cm3/50 sec = 1cm3/sec
Difference:-.1 cm3/sec
Trial 2
26 cm3/10 sec = 2.6cm3/sec
66 cm3/50 sec = 1.320cm3/sec
Difference: -1.28cm3/sec
Hydrochloric acid (2 mol dm-3)
Trial 1
50 cm3/10 sec = 5cm3/sec
71 cm3/30 sec = 2.367cm3/sec
Difference: -2.633 cm3/sec
Trial 2
55 cm3/10 sec = 5.5cm3/sec
87 cm3/30 sec = 2.9cm3/sec
Difference: -.2.6cm3/sec
Sulphuric acid (1 mol dm-3)
Trial 1
26 cm3/10 sec = 2.6cm3/sec
69 cm3/50 sec = 1.3cm3/sec
Difference: -1.3 cm3/sec
Trial 2
27 cm3/10 sec = 2.7cm3/sec
69 cm3/50 sec = 1.3cm3/sec
Difference: -.1.4 cm3/sec
Looking at the results from the experiment and the calculations done to figure out what the rate of reaction was per second, we are able to see that the starting rate of reaction is greater than the rate of reaction halfway through the experiment. This is so due to the fact that in the beginning of the experiment there is more surface area and mass of magnesium, then halfway through the experiment which is lower. We are also able to come to the deduction that a concentration of 2 moles of Hydrogen Chloride is far more effective at reacting with Magnesium (in terms of time), then a 1 mole concentration of the same. Increasing the concentration will in turn increase the frequency of the collisions between the two reactants.
Sulphuric acid although a more powerful acid then Hydrochloric acid, is not able compete with 2mol dm-3 of Hydrochloric acid. Thus making it the second fastest reactant with Magnesium.
Conclusion: After analysing the results it is possible to understand where I went wrong in the hypothesis. After reading the hypothesis I have come to the conclusion that my hypothesis was correct to an extent, that it can be considered correct. It is not very clear in my hypothesis the explanation of why Sulphuric acid is not going to have a better reaction than Hydrochloric acid, the reason for this is because I did not understand why it would be like so. But after completing the experiment I have come to realise that 2mol dm-3 Hydrochloric acid is much faster at reacting, because 2 molar concentration means that there is double the molecules than a 1 mol concentration of Sulphuric acid. This means that there will be double the crashes than that of Sulphuric acid. Taking all of this into account and the difference between Trials 1 and 2 I would say my Hypothesis is averagely reliable.
In terms of validity, I would say that this experiment was not very accurate, there were many mistakes made during the experiment. One of which was the fact that the surface area of the Magnesium and the mass were not the same for every coil of Magnesium used, another variable we were not controlling was the temperature. As the experiment was unfoldingwe could see that the temperature of the substance was increasing, not able to think about what to do at the moment we decided to proceed with the experiment and then rule out temperature. We came to the conclusion that the temperature would not alter the results of the experiment, but it turns out it did. Another variable that was nearly impossible to control was the time it took for us to cap the bong so that none of the gas was leaked. I was able to recognise that the second member of the group that was in charge of capping the bong, was faster than the other member that was in charge of doing this in the first trials. What we should have done to create a more valid experiment was to use the same member for the job; this would still change the time, but would insure a better result.
Evaluation: The main weakness of my experiment was the temperature change and the gas leakage. These were the most important changes that altered the results, although there really nothing we could do to improve the leakage we could have had a time of about 5 seconds after we dropped in the magnesium coil to closing the bong. This would not mislead the experiment and then we would have much better results (even though there was some leaking gas in the 5 second period). To control the temperature we should have used a Bunsen burner and heat the substance, thus having a temperature that would remain stable throughout the experiment, and also improve further our results.
To make the experiment more interesting we could have Sulphuric acid of 2mol dm-3 this we would then be able to pose the question of which acid is stronger. Doing this can improve our knowledge of whether; an acid with a bigger molecular mass has a faster rate of reaction then an acid with a lower molecular mass. To further improve this investigation, we could also add another acid with an increased molecular mass.
