Hypothesis – The idea I aim to test in this experiment is the relationship between the mass of magnesium and mass of oxygen once the magnesium has been heated and reacted with the oxygen. There will be 3 variables in this experiment. The independent variable will be the mass of magnesium ribbon as different measurements will be taken and used for each trial.
The dependant variable will be the mass of Magnesium Oxide, this is a measured variable as the mass of oxygen can be calculated and will enable us to determine the formula for Magnesium Oxide. The controlled variable is that the Magnesium used is possibly from the same ribbon and after being cut into lengths was stored in the same way in plastic containers. Preliminary – I originally did a preliminary test with Iron wool where we used a similar method but Testthe iron wool was held over the flame by tongs and not contained within a crucible.
We learnt from this experiment the importance of the crucible to contain all of the metal for an accurate test because the iron wool broke off as it heated and we were left with a lot of the iron wool on the bench mats around the Bunsen burner so our calculation of the mass of iron oxide was not accurate as we had not contained all the wool and couldn’t accurately collect the pieces around that had come away, therefore no giving a true mass of Iron Oxide. Prediction – I predict that when the magnesium and the Oxygen combine and react together the magnesium will oxidise and become heavier.
I expect to see a straight line pattern from these results as I believe the more Magnesium there is the more Oxygen it will take on to form the Magnesium Oxide and so believe the results should gradually get heavier and heavier as the Magnesium gets heavier and heavier. The equation for this investigation would be Mg + O2 ?MgO which would balance as 2Mg + O2 ? 2MgO. This is done as the Oxygen has two molecules which would need two Magnesium molecules to balance it out. The physical changes I expect to take place are heat and light as I expect the Magnesium to change colour as it is heated up and reacts with the Oxygen.
The Chemical changes I expect to take place are that a new substance will be made and a new formula will be formed. A new substance will be made in the form of smoke and the new formula will be MgO. Apparatus – *Goggles*Crucible and Lid *Bench Mat*Tongs *Tripod*Varied lengths of Magnesium ribbon *Bunsen burner*Scales *Pipe-clay triangle*200g weight Method – All the apparatus was set up to ensure that the experiment was carried out safely. Goggles were worn and the bench mat was put in place in case any sparks or parts of the experiment went wrong to protect our eyes and the work surface.
The tripod and pipe clay triangle were used to keep the crucible safely above the heat. The Bunsen burner was used to heat the magnesium and was set to a fierce blue flame. The crucible held the Magnesium above the Bunsen burner, and the lid contained as much smoke as possible to help the reaction to take place. The crucible lid and tongs were used to occasionally let in the oxygen and then replace the lid safely. The apparatus was set up as above and as per the diagram to being the experiment. I first checked the scales using a 200g weight to check their accuracy.
When I weighed the 200g weight on the scales prior to the experiment the scales weighed in at 1. 038kg however, as this was a large weight by comparison to my crucible I didn’t account for this slight measurement in my results as I decided it would make the calculations too low as my crucible was only a fraction of the weight of 200g and so for the purposes of this experiment wouldn’t alter my results enough to justify it. I then measured the crucible without the lid to find out its mass (22. 27g), once recorded I then measured the Magnesium ribbon (0. 9g) I then measured the two together to check the accuracy and got a mass of 22. 56g which meant my previous measurements were reliable. The next step was to put the crucible with the magnesium inside and the lid on onto the pipe clay triangle above the fierce blue flame of the Bunsen burner. The lid remained on only except for occasionally lifting it and quickly replacing it to let more oxygen into the magnesium but to try and keep as much smoke in as possible. Once the Magnesium Oxide stopped smoking when the lid was lifted the experiment was complete and I turned off the flame and left the crucible to cool.
Once cooled I weighed the crucible with the newly formed Magnesium oxide (22. 72g) and then was able to subtract my previous figure of 22. 56g from this to give a difference of 0. 16g. This 0. 16g was my mass of Oxygen. Results – It can be seen from the results that there is a direct relationship between the mass of Magnesium to start with and the mass of Oxygen in the Magnesium Oxide. Using my results I worked out the ratio between Magnesium and Oxygen, from these results it suggests that the ratio is 1. 2 moles of Magnesium to 1 mole of Oxygen. However you cannot have 1. of an atom and so these results can be rounded up to a ratio of 1:1 which would reflect the equation I had predicted of MgO. Conclusion – The mass of Magnesium got heavier in my experiment by 0. 16g because the Magnesium joined with the Oxygen. Other students’ result ranged from 0. 09 – 0. 46 and apart from one anomalous result the heavier the Magnesium was the higher the mass of Oxygen was. Each measure of Magnesium was only tried once and each measurement was done by an individual and so this may account for the random errors in our findings as shown on the graph, but overall our results were fairly evenly spread.
From the results I was able to plot a straight line graph by using a line of best fit; which ran parallel to the theoretical line of best fit. My predictions for this experiment were right as the results show that the more Magnesium ribbon that was used the more oxygen was needed to react with it and so the gradient was steady at about a 450 angle gradually increasing in mass as the Magnesium mass increased. I would say there was one anomalous result as it was significantly below the line of best fit but this can be put down to a number of things such as different scales being used, different people doing each result or simple human error.
Our line of best fit was slightly below the theoretical line of best fit for this experiment and I mainly believe this could be due to a systematic error such as the scales we used not being precisely accurate. This may however account for the systematic error of the line of best fit being lower than the theoretical line as that slight change along with random errors may have lowered the results; but the results were still valid as the line of best fit was parallel to the theoretical line meaning we had a constant of the scales being slightly light. As can be seen from the results of our Spearman’s rho and Chi Tests our results were within % of the theoretical results and so this suggests we did an accurate and valid test. We did the Spearman’s rho test as this is a measure of the linear relationship between the two variables and shows us that there is a connection between our results and the theoretical ones. The Spearman’s Rho test shows the accuracy of our results and our calculation came in at 98. 7% so it proves our results were very accurate. We did the Chi squared test as this determined whether there was a significant different between the theoretical frequencies and the observed/practical frequencies comparing the validity of the results.
At least 95% result in the Chi-squared test would prove to be valid and our result was 99. 99% so it shows our results were definitely valid according to the chi-squared test. We did the Spearman’s and Chi-squared tests via the Excel calculations as shown on the table of results. Evaluation – Overall our results were very accurate but there were some random and systematic errors which could be reduced or resolved if we did further experiments. We could have done re-tests for all the Magnesium masses and taken a mean average of those results to get a more accurate reading this would possibly have reduced any systematic errors.
I made the test fair by taking the measurements of the crucible and lid and keeping them the same so that I can compare the results between the Magnesium and Oxygen. Also if the same person had carried out each experiment instead of each student doing a different measurement it may have been more accurate as the method may have changed slightly between each student, for example, one person may have lifted the lid a lot more frequently of for longer periods than another.
The difference in the scales will also account for the systematic error as shown on the graph. Also the amount of smoke which was let out during each experiment will have varied between each student as the results were being gathered individually and the amount of smoke which escaped may account for some random errors within our results which is why our results are not all as in line as the theoretical results.
And e had to find a line of best fit rather than a clear line which went through each individual result as the theory would suggest. If I were to do this experiment again I would repeat the tests with each mass of Magnesium and take a mean average so as to achieve a more accurate result I would also ensure that each mass of magnesium was the same; as in our experiment some students coiled the Magnesium up in the crucible and others ripped it into little strips.
By placing the Magnesium in the crucible in different ways it may affect how much oxygen can get to the ribbon, if it is coiled up for example it may need to be prodded and moved to allow all the Magnesium to have exposure to the Oxygen whereas the smaller strips may be more exposed without as much intervention. On both accounts though if you do need to prod the magnesium in that time you may be letting a lot of smoke out as the lid would obviously need to be off the crucible and so this would also need to be taken into consideration.
This is why if the magnesium was placed in the crucible in exactly the same way it would make the results more accurate. To take it one step further you could time the lifting of the lid to make it more accurate, for example, lifting it every 30 seconds for a period of say 2 seconds would mean that each mass of Magnesium would be getting the same time exposed to the oxygen and so a more accurate reading of the amount of Oxygen it gains would be achieved if this was carried out with a stop watch.
Also if I were to improve the investigation for next time I would increase the number of Magnesium Masses used to gain a more accurate result and having more results would also make any anomalous results stand out and also expose more random and systematic errors which could be dealt with.