T-Test
T = [xA – xB]
√SDA2 + SDB2
n n
T = [20.01 – 21.69]
√2.772 + 1.172
5 5
T = -1.68
√1.53 + 0.27
T = -1.68
1.8
T = 0.93
Now, using degrees of freedom in relation to my results from the T test, I will calculate whether or not the difference between the two sets of results is significant. The value of ‘t’ I calculated was 0.93. Using this figure I can read from the table of ‘t distribution’, and deduce that because my figure is greater than 0.05, the difference in results is not significant.
However, the differences in individual and mean results along with the scientific knowledge I possess, suggests otherwise. The more rapid descent of the skimmed milk suggests it has a higher density than the homogenised. Using the scientific knowledge I have gathered, I can deduce that homogenised milk is less dense as it contains a lot more lipids (fat). The fat is dispersed throughout the milk in globules. These globules have a lower specific gravity and cause the homogenised milk to fall slower than the skimmed milk. Because the fat globules have a lower specific gravity, they are lighter than the milk serum. So, the globules rise to the top and skimmed milk is produced by ‘skimming’ the fat from the top of the milk. This lack of fat globules explains why the skimmed milk falls quicker through the copper(II) sulphate solution.
Evaluation
Due to my results not correlating with my use of scientific knowledge, there must be problems with this experiment. One such problem is that of being able to produce exactly one drop of milk from the syringe when required.
In addition to this particular problem, it was excessively difficult to ensure that each drop was of identical volume.
Another problem was the difficulty of judging when the drop of milk was exactly on the 100cm3 mark and the 10cm3 mark, in order to start and stop the watch.
Another problem was that I was completely inexperienced in the operating of the syringe, which meant that in was difficult to produce identical drops and this may have resulted in inaccurate results.
The limitations that I believe to be major are; producing one single drop at a time, and ensuring that all drops produced are of identical size and volume.
To overcome the both of these limitations, there are two possible solutions. The first of these is practicing the use of the syringe prior to carrying out the experiment. The second possible solution is to use a syringe of better quality and accuracy.
I encountered one result, which could be considered to be anomalous. My result of 23.53 seconds from full fat milk differs enough from the other results of full fat milk, for me to consider it to be anomalous. This result may have been caused by poor accuracy of timing, or differing drop sizes/volumes.
The full fat milk had a relatively short range (1.32 seconds, not including anomalous result), in contrast to the larger range of the semi-skimmed milk (7.21 seconds). However, the semi-skimmed milk produced no anomalous results.
To increase the accuracy and reliability of my results, there are numerous improvements that could be made. One such improvement would be to the increase repetitions of the procedure. For example, gather 10 results for each type of milk, rather than 5.
Another possible improvement would be to repeat the entire experiment numerous times and calculate mean results. This would improve the reliability of the results gathered.
Other improvements could be to use a more accurate syringe, and to ensure that I was well practiced in using the syringe before carrying out the experiment.
