Hypothesis:
I think that there will be a direct relationship between the mass of magnesium to begin with and the mass of oxygen at the end. I think that this will be the case because I believe that if there is more magnesium then there is going to be more reaction going on which in turn will mean a higher mass of oxygen in the magnesium oxide.
Apparatus:
Tripod
Heatproof mat
Bunsen burner
Crucible and lid
Scales
Pipe Clay Triangle
Diagram:
Method:
We Set up all our apparatus as above and put on our safety goggles. First of all we had to weigh our crucibles to find their mass, we recorded this and collected some magnesium ribbon, which we placed in the crucible, and then re-weighed and found the weight of magnesium we had. I did this by subtracting the weight of the crucible on its own from the new weight.
The next step was to put the crucible on top of the tripod with the lid on. We needed to leave the lid on for a while because of the fact that magnesium oxide was escaping in the form of smoke. We heated the magnesium with a roaring flame and when it stopped flaring up we took the lid off of the crucible.
After this we had to weigh the crucible and record the result, before we weighed it we had to let it cool down because heat can cause distortions on the scales. To make sure that all of the magnesium was reacted we heated it for a bit more and weighed it again, when the two masses were the same we knew that it had finished.
The whole reason for us doing this investigation is because we wanted to know the relationship between the amount of magnesium to start with and the mass of gained oxygen, to do this we took the weight of the crucible containing the magnesium oxide and subtracted the weight of the crucible containing just magnesium.
When we had done one experiment we tapped out what we could of the magnesium oxide and re-weighed the crucible. We did this process until we had a suitable set of results.
Analysis:
From my graph I have found that my hypothesis was indeed correct because there is a direct relationship between the mass of magnesium to start with and the mass of oxygen in the magnesium oxide. I found this out from my graphs. This means that the more magnesium you start with, the more oxygen is present at the end.
Using my results I worked out the ratio between the magnesium and the oxygen, my results suggest that the ratio is roughly 1 mole of magnesium to 0.8 moles of oxygen. From this result I find the formula Mg O . I worked this out by finding a point on the graph that the line of best fit goes through and using this as the ratio. Then to get the formula I turned the ratio into a fraction and took the numerator and denominator as the number of atoms.
Evaluation:
Our results are all out, but they are in correlation, which suggests that the same mistake was made over and over again. I know that the results are wrong because due to prior knowledge I already knew that the formula of magnesium oxide is MgO. The results I have obtained show that less oxygen has reacted with the magnesium than was expected. There could be many explanations for these consistent dodgy results, here are the ones which I believe we may be at fault for:
- The first possibility is that as we used magnesium ribbon, only the outer shell oxidized meaning that the core was still magnesium. This would affect the results because less oxygen atoms have bonded with magnesium atoms. If I did the experiment again then I would use the powdered form of magnesium and the results would be more accurate.
- The second thing I can think of is that when we took the lid off there was a deposit of magnesium oxide on the underside of the lid; this could have affected the results slightly. I don’t really know a way around this one because if we took the lid off then the MgO would just escape. I think that the best way to do it is to put the lid on at the start and when we take it off we could collect the deposits and put it all back in the crucible.
- I also think that we left the lid on for too long as we didn’t let much oxygen get in and the magnesium needs oxygen to oxidize. If I re-did the investigation I would take the lid off a lot sooner but also taking the above point into consideration.
Apart from these slight mistakes, which can always be altered, the investigation on a whole went reasonably well and the way we carried out the experiments was really good and efficient as we got 10 sets of results in order to give us a more accurate graph.
