Now that I was satisfied with my preliminary results I decide to start taking some more accurate measurements using the results from my preliminary experiment. The apparatus is drawn below.
When heating the experiment I discovered my next problem. Whilst heating the experiment in a water bath, the Pyrex beaker cracked at 74°C. As Pyrex beakers are made to withstand high temperatures I decided that the crack must have been due to (mechanical). I then discovered that as the experiment was being heated there was a bubble of energy forming under the dome shaped bottom of the jar. When the bubble became big enough it lifted the jar in the water bath and dropped it in the bath, causing the crack. I therefore decided to heat the water bath to boiling first, turn of the flame, then slowly hold the jar in the bath until it was warmed, and then slowly lowered the jar into the bath. I left the jar until the temperature of the syrup was about the same as the temperature of the water, which took around 5-10 minutes. I repeated this until the syrup was 75°C. I then rolled the jar down the slope and recorded the times taken at 2°C intervals. The results are shown below in table and graph form.
As I expected, the jar rolled faster at higher temperatures and slower at lower temperatures. At 0°C, the syrup was solid across one side of the jar. At this point the jar would not roll at all (this result is not shown on the graph so as not to effect the line of best fit). This was again because of the centre of gravity and the affect it has on the turning force. As the syrup cannot flow the centre of gravity settles directly above the contact point of the slope and the jar and will not move. The quicker the mass changes from one side of the jar to another the quicker the jar will role down the slope. This is shown in the diagram below.
The Boltzmann Factor: The Boltzmann factor explains why the syrup flows quicker when warmer. It tells us that if a molecule is given enough energy (in this case by the heat energy) then it can break free from its surrounding molecules and flow. The more energy the flame gives the molecules the quicker they can flow into new positions. The formula for this is E/kT where E is the activation energy required to break the bonds between two molecules and kT is a constant (k)(depending on the liquid) and T the temperature in Kelvin’s. The formula shows that if kT is greater than E then the liquid will flow. As we do not know the constant we cannot work out the activation energy. Despite this the results still show that this is what is happening. This is relevant to this experiment as the higher the temperature the more energy the molecules will flow, so the syrup will flow easier.
Anomalies: There were many places in my experiment where errors could have occurred. For example, when measuring the temperature of the syrup I removed some that was stuck to the thermometer. I scraped of as much as possible, but still some remained on the thermometer. Because of this I think my results are accurate to the nearest gram of syrup. The two most obvious places where inaccuracies could have occurred were, the constantly changing temperature and timing using my reactions. I think that these inaccuracies are minor and did not affect the results of the experiment in an important way. The results that I feel show this are the 64 and 66°C results where the jar appears to go faster as the temperature decreases. Because of this I have decided to ignore these results. Another major inaccuracy is in the grains of the slope, as it was not perfectly smooth. I think that although the grains may have slowed the jar down at some points, the jar then accelerated rapidly after this, so the average speed was about the same. However I cannot prove this so I will repeat some of the experiment on a metallic surface to see if I get the same results.
Repeat: To repeat the experiment I shall use a metallic runway to stop friction from the slope affecting my results. Having one some preliminary rolls, I realised that the slope I was using, which was thinner than the other slope, meant that the jar repeatedly got jammed against the edges. I therefore decided to roll the jar 20cm, and use average velocities to compare my original results with my new results. I also decided to only repeat the experiment between 30-50°C, as these seemed a particular place of interest in the experiment. My results from the repeats are shown below.
Conclusion: Despite these errors I still feel my results are/Are not accurate (I will repeat exp. Using metallic surface. The points between 30-50°C Show a clear change from a low velocity to a high velocity. I therefore concluded that this is comparable to activation energy. Activation energy is where a molecule has enough energy to perform a reaction. In this case the molecules have enough energy to change state from a very viscous liquid to a much less viscous liquid.
