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Comparing the Density of Skimmed and Homogenised Milk

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Introduction

Comparing the Density of Skimmed and Homogenised Milk Results Skimmed Milk Sample x (x - x) (x - x)2 1 21.75 1.74 3.03 2 16.6 -3.41 11.69 3 23.81 3.8 14.44 4 19.31 -0.7 0.49 5 18.97 -1.04 1.08 Mean 20.01 30.73 Homogenised Milk Sample x (x - x) (x - x)2 1 21.94 0.25 0.06 2 21.57 -0.12 0.01 3 23.53 1.84 3.39 4 20.78 -0.91 0.83 5 20.62 -1.07 1.14 Mean 21.69 5.43 Analysis The mean results were; 20.01 seconds for skimmed milk, and 21.69 seconds for homogenised milk. This indicates that skimmed milk may have a higher density than that of homogenised milk, as it falls faster through the copper(II) sulphate solution. To attempt to verify this, I will find the standard deviation of both sets of results. This will make it more certain to establish whether or not the densities are significantly different. Standard Deviation Skimmed milk V?(x - x)2 N - 1 V30.73 4 = 2.77 (2 d.p.) ...read more.

Middle

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. ...read more.

Conclusion

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. Dean Armstrong ...read more.

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