Water (H2O)
Method
Firstly, I will take five magnesium ribbons. Using the ruler and scissors, I will measure and cut them until they are exactly 5 cm long. Once done, I will, using a measuring cylinder, measure out the volume of hydrochloric acid and, using a second measuring cylinder, measure out the volume of water needed to produce the required concentration of hydrochloric acid. I will then proceed to pour the two liquids into the conical flask. I shall then drop a piece of magnesium ribbon into the conical flask, quickly stopper it with the tube connected to the gas syringe used for measuring gas in units of cubic centimetres, start the stop watch, and wait until 35 cc of hydrogen has been produced. I will then stop the stop watch and see how long it took to produce it. I will then repeat the experiment with varying relative quantities of hydrochloric acid and water, to produce different concentrations. To ensure this experiment is fair, I will use the same conical flask, measuring cylinders, gas syringe and stop watch. To ensure this experiment is safe, I shall wear protective goggles.
Results
Observations: The acid bubbled vigorously when the magnesium was dropped in, and the conical flask went cloudy. Afterwards, the conical flask had a sharp, tinny, strong smell to it.
Analysing evidence
I have produced a graph to show the results in the form of a line graph. The results have shown that there is not a straight line correlation between concentration of HCl and the time taken to produce 35 cc of hydrogen. The reason why I did this as a line which passes through all the plotted points instead of a line of best fit is that a line of best fit would not accurately show the results from this experiment.
The line through the plotted points shows that there was an unexpected result, in as much as lower concentrations of HCl produced a time not in proportion to that of higher concentrations suggesting that there is a minimum level of concentration required to create a baseline.
Conclusion: The first time we preformed the experiment, for 1, 1.5 and 2 moles the time it took to produce 35cm cubed of hydrogen was one second more than twice the previous result, for example 2 moles = 6 seconds, 1.5 moles = 2x6+1 seconds = 13 seconds. However, for 0.5 moles, it took 133 seconds to produce 35cm cubed of hydrogen, which proves that the relationship between reaction times does not work for all results. The second time we preformed the experiment, for 2 and 1.5 moles the relationship of the early tests in the previous experiments proved true, however for the difference between 1.5 and 1 mole, this relationship did not prove true. This suggests that either there is no exact relationship between the reaction times or that there was an error in the result. In fact, the only fixed trend we could demonstrate in the results was the lower the concentration, the longer it took to produce the desired amount of hydrogen. This is explained by the collision theory. Because there is more water in the lesser concentration of acid, the HCl ions are further apart, and so they will not collide with the magnesium as often. This matches my original prediction, which stated that the higher the concentration of the hydrochloric acid is, the shorter the time it will take to produce 35 cc of hydrogen.
Evaluation: On the whole, I think the experiment was accurately carried out. The only two areas of the experiment I feel unhappy with are the results for the tests using A) 50 cc of water and 50 cc of hydrochloric acid (1 Mole) and, B) 75 cc of water and 25 cc of hydrochloric acid (0.5 Mole). A) because the difference between the results in both experiments was out of line with the other concentrations and B) because of the change in the relationship of the time taken to produce 35 cc of hydrogen, between 1 Mole and 0.5 Moles concentration. I think that if I were to repeat the experiment, I would do more experiments between the 1 mole and 0.5 moles range, at more regular intervals e.g. 1 mole, 0.9 moles, 0.8 moles, 0.7 moles etc. I believe that by doing so I would be able to identify the huge jump in time, making it more gradual between experiment times. I could even pin point where the biggest jump is, and repeat that test to determine what makes it jump. The readings, with the exception of the test using 1 Mole in the second experiment, were, I felt, accurate, but not as accurate as they could be, as our stopwatch did not have split seconds. In future I shall use a stopwatch with split seconds to make the more reading more accurate.