Runny Oils Coursework

There will only be one controlled variable in this experiment and that is the chain length of the oils we use. For accurate results we will be using 5 different oils, these are: C6, C8, C10, C12, and C16. We are unable to use a C14 oil but hopefully the graphs plotted from the results will allow us to see what result we would have gained from a C14 oil.

Everything else in the experiment will be kept a constant. That is the angle of the tube, the ball bearings, and the same person stopping and starting the clock. To ensure that our results are even more accurate and reliable we will run the test through once before we actually start to take any results. This is because when the ball bearings have been in the oil once it is extremely difficult to remove all the particles of oil, there will always be an oily residue left on the ball. So the only way to solve this would be to ensure that before taking any results the ball already has this thin layer of oil over it for every different test on each of the oils. In addition to this it is important that the ball is placed into the tube right at the top and left to roll down - pushing the ball down into the tube will provide inaccurate results.

Prediction:

I predict that as the chain length of an oil increases, the runniness of the oil will decrease, (the ball bearing will take longer to travel through the oil). If you compare a hexane molecule (C8 H12) to an octane molecule (C8H18) it is clear that the octane molecule has more carbon atoms and hydrogen atoms:

The difference between them is to do with the overall size of the molecule. Therefore, as there are altogether more atoms, and the molecule is bigger (longer chain length) the oil will be denser and thicker. This proves that as the chain length increases, so does the density of the oil and so the ball bearing will take longer to travel through it.

Keeping all of the above points in mind about fairness we will carry out our experiment as accurately as possible. Firstly, we will ensure each ball bearing we use has a thin coated layer of oil on it. Then we will once by one test the runniness of each oil by dropping the ball down the tube and timing how long it takes to reach the finish point. This will be done 5 times for each oil to obtain accurate results from which we can take averages from.

Results:

In gathering the results we encountered no major problems. The equipment was set up as we had planned, (as we found out from our preliminary work) and the results we obtained initially seemed to fit with the prediction. We ensured that each one of us kept the same job throughout the whole experiment. For example: Myself measuring amounts of oil, Matthew timing the run of the ball and Mark recording the results. We realised that to obtain accurate results the person timing the run of the ball would also have to be the one watching the run of it. We found that it wouldn't be as accurate if one person timed and one person called out when it passed the start and stop point. We realised this from doing our preliminary work.

Also as we had to take the tube out of the clamp stand each time for a different oil we made sure that the angle wasn't adjusted each time in removing and replacing the tube. To ensure this we also had a mark on the tube showing us how far to slide it back into the clamp, thus making sure the angle was kept the same. We had to take it out each time for the new oil as we found it difficult to squirt the oil in with the pipette when the tube was at a 15° angle. It wasn't impossible but throughout the preliminary work little droplets of oil were often spilled when trying to get it into the tube. In addition to this we found it a lot more accurate dropping the oil in when the tube was vertical. When dropping it in at the angle the oil left a thick residue along the bottom of the tube, this is where the ball was rolling. This would have made obtaining our evidence far less accurate if we had done it this way as each time the oil would have been laying along the bottom of the tube from top to bottom. This would have stopped the ball from picking up a small pace which is what we planned for it to do. We managed to complete the whole experiment within one lesson, this made the results that more accurate for many reasons. If we had had to set the equipment up all over again it is very unlikely that we would have got it set up identically to the first time. Below are the results we obtained:-

Oil

Average Time Taken For Ball Bearing To Reach Finish (seconds)

C6

.34

C8

.94

C10

3.31

C12

4.49

C16

8.69

When carrying out the experiment we only had time in that one lesson to record 3 sets of results for each oil, instead of the original plan to do 5. However, we felt that it would be more accurate if we just left it at 3 in the one lesson that doing each one 5 times over 2 lessons. If we had done this it is extremely likely that the results from the second lesson would not have fit the trend we were seeing from lesson 1. And also the results we got from doing each one 3 times were still far more accurate than we first thought they would be - an obvious trend was apparent that we didn't think we would have initially seen in only doing it 3 times.

In addition to simply timing how long it takes for the ball bearing to hit the finish line we also took into account the speed of the ball. This is why we made the distance of the ball to travel 10cm - a round number that would make working out the speed more accurate. Using the formula: SPEED = DISTANCE we calculated these results: TIME

Oil

Average Speed Ball Bearing Travelled At Through Tube (cm/s)

C6

7.46

C8

5.15

C10

3.02

C12

2.23

C16

.15

Conclusion:

From this experiment there is conclusive evidence to prove that as the chain length increases the runniness of the oil decreases. The two values are inversely proportional to each other, as one increases the other decreases. We can see from looking at the results and graphs that as the oil gets thicker it takes longer and longer for the ball to pass through the oil, not only does it take longer but the increments increase too. It is clear on the graph (especially the speed graph) that the curve is becoming more and more horizontal as it gets to the bottom. This shows that if we went on and on testing oils of greater chain length the ball bearing eventually wouldn't even move through it.

My results have shown and proven my prediction to be correct. As the chain length increases it does make the oil thicker and less runny. This is because the molecules get bigger and therefore there is much less space for the ball bearing to slide between down the tube:

e.g.

The oil becomes a lot more dense as the chain length increases, thus slowing down the ball as results show. This explains why eventually the ball would stop if we were to continue testing using a greater range of chain lengths. However this is only the case with using the 15° angle, the ball wouldn't stop as easily if the angle was increased, but we chose this angle for the range of chains we were using and it worked effectively.

Evaluation:

For this particular apparatus and the way this apparatus is set up it can be said that the results obtained are very accurate. The method I used has proved to give far more reliable results than method 1 (dribbling the oil down a slide). The results from this experiment that we have gained are for more accurate than we had planned from doing the preliminary work. We thought we would have had to done the experiment more times to get reliable readings, but as our results show, 3 was a sufficient amount of times to test each oil.

However if we were to do this experiment again it is unlikely to obtain the same results, I believe that they would still be fair but not the same. There are so many fixed variables that if altered slightly would change the outcome of the results. For example: if the 15° would be hard to measure out again, the way I dropped the oil into the tube could affect the results and so could many other factors. Although this is the case if the angle wasn't exactly the same as long as it was at that throughout the experiment and everything else was correctly kept constant then the results should be just as accurate as the results we obtained, but each actual individual result would be different.

There is one anomalous result that is clearly shown in every graph and chart drawn. It becomes apparent that the C10 oil doesn't fit the curve of the graphs. It is most clearly shown on the speed graph that this is an anomaly. There are few possible explanations for this, the simple obvious one being that the experiment was done enough times. But looking at the rest of the results it's fair to say the experiment was carried out enough times. Another more likely explanation is that we had to test the C10 after we had tested the C16 oil. We couldn't help but do it this way as we had to share the oils around the class. In doing the C10 after an oil with greater chain length it showed clearly in our results which we didn't think it would. The C16 would have left a residue just like all the oils do, but as it's a thicker residue than the oil we were actually testing this would have been what slowed the ball down. From the speed graph we can see that the C10 speed isn't quick enough to fit in with the trend.

From the results and graphs it is possible to work out what values C14 would have given us. Here are the tables with the estimated value of what C14 is likely to be:

Oil

Average Time Taken For Ball Bearing To Reach Finish (seconds)

C6

.34

C8

.94

C10

3.31

C12

4.49

C14

6.41

C16

8.69

Oil

Average Speed Ball Bearing Travelled At Through Tube (cm/s)

C6

7.46

C8

5.15

C10

3.02

C12

2.23

C14

.55

C16

.15

Just by looking at the results tables we can see that the C14 oil fits in, and these are the values we would be very likely to obtain if we did C14.

Much more further work can be done on this experiment to improve the accuracy of the results and to support a more firm conclusion. Firstly investigating how the angle of the tube affects the speed the ball travels through the oil would be necessary. This needs to be done accurately, we did not have enough time to do this as we soon found a suitable angle through the preliminary work. However it is important to research this as a different angle may give more reliable results.

If we could repeat the experiment I would ensure to do each oil in an ascending order, rather than testing which ever one is available. When we did this we realised that it may have some affect but not to the extent that it produced such an obvious anomalous result. There is little point in just testing C10 again as neither the tube or the ball bearings will have oily residues on them. The only way to do it is to do the experiment again, but making sure to do each oil in ascending order C6 - C16. It is obviously important that each oil is done in order starting with C6. As well as this if we did it again we could test how reliable the results actually are by testing for C14. We would then be able to see how accurate and precise not only our results are but our graphs too.

Our results may also be unreliable as we left the ball bearings we rolled at the bottom of the tube each time. As we only did it 3 times for each oil there were only 2 ball bearings laying at the bottom of the tube instead of 4 which we had originally planned. We realised that if we left the ball bearings in the bottom each time it would increase the level of oil in the tube - therefore when the ball rolled down it hit the oil at an earlier stage:

Although this was the case we felt that this would give more accurate results than tipping the oil out each time to get the ball from the bottom. The only way we could have made this more accurate and reliable is to find some way of getting the ball bearing out without disturbing the oil in the tube. We new from the outset that this would be a problem, and from preliminary work we found that the way we did it was the best we could do with the apparatus available.