Evaluation
The accuracy of the equipment we used in the experiment could mean our results are not as accurate as they could be.
Firstly we used a balance to weigh the beaker and milk. If the measurements we incorrect from the start, it would mean that our results would be sure to be wrong. As we used the balance more the once, the less accurate our results are.
To find the error for the equipment we use a simple calculation
Firstly you find the smallest measurement the equipment will measure, then divide it by two, this is the error. Insert this number into this equation.
We can use this equation for any measuring instrument. This finds the % error and so we know how accurate or inaccurate out results are.
Skimmed milk
Smallest reading of the balance: 0.001÷2=0.0005
Unknown milk
Smallest reading of the balance: 0.001÷2=0.0005
As the percentage error is of such a small degree, this would mean we can be sure that our results are of a small degree inaccurate but the result could be either plus or minus this value.
Procedural error could cause some degree of inaccuracy. Although we cannot calculate the percentage error of the procedural errors, they still contribute in our results been inaccurate.
Within the following procedure we lost most material
- Once the mixture was cooled a beaker was set up with muslin and filtered the protein and fat the dried between filter paper. The solid was the placed in a clean dry 250cm³ beaker
Firstly the mixture was poured into the filter and a small amount of fat and protein were left in the beaker, then again once we had filtered the mixture on the muslin. Placing the fat and protein on the filter paper results in more protein and fat been lost when placing it back into a beaker. At several other points within the experiment my mixture was transferred, even if there is only a small amount of the mixture left in each, the end result would be a considerably large amount of protein and fat been lost.
The results of our protein could be inaccurate as in the procedure
- The beaker was placed on a hot plate and ethanoic acid was added and stirred until the fat and protein in the milk began precipitate
The protein may not have coagulated as we may not have heated the mixture for long enough or we may not have stirred it.
The results for out fat could be inaccurate due to the need for the fat to stick to the protein, so if this didn’t happen fully, immediately some fat would be filtered off. Not all the fat that was stuck to the protein separated as when we used propanone to do solvent extraction, if the surface area of the protein was small if we didn’t break the protein up enough the amount of fat released was reduced as the propanone could not reach the fat that was in the centre of the large pieces of protein.
Along with the errors within the procedure, we lost a large amount of protein as when we used the reduced pressure filter we pulled the Buchner funnel out of the flask and spilt the protein. Because of this our protein value could be lower then thought.
Although there were many procedural errors, within my experiment i did carry out some actions to ensure accuracy. Firstly I used an ice bath to cool down the mixture before filtering it.
Secondly I weighed the beakers before putting the mixture in it at several points, doing this means the amount of time the mixture was transferred between beakers was reduced, resulting in less of the mixture been lost.
Also we used muslin to filter the mixture. Using muslin, instead of filter paper, ensures that is doesn’t get blocked up stopping any molecules through.
To increase the accuracy of our results there are several actions we could carry out. Firstly when we are heating the protein and fat with the acid, we could stir the mixture which would increase the rate of which they coagulate. Also we could heat the mixture for longer.
Secondly if we break the protein up once we have added the propanone then as the surface area will have been increased the rate of which the protein and fat separate will increase as the propanone will be able to reach more fat molecules within the protein.
Also to ensure the measurements of the milk and propanone are accurate use a burette, which has a larger degree of accuracy.
Conclusion
Within my experiment I found the value of skimmed milk and unknown milk. I carried out an experiment of which gave me a value for the amount of lipids and protein in each. Here is a copy of my re-sults:
Firstly I did skimmed milk in which I found the mass of protein was 2.38 making the percentage of protein remaining at the end of the experiment 2.581%. The fat of the skimmed milk was 0%.The unknown milks results were 2.318% of protein and a mass of 2.07 and the fat had a mass of 0.39 and a percentage of 0.437. The results show that that the percentage of protein in the skimmed and unknown milk is very similar with a difference of 0.263% where as the fat has a larger difference between the two.
The results I obtained need to be compared to literature values.
Literature values:
Looking at the literature results and my results I can see that both the protein and lipid values of my results are noticeably lower as my results of skimmed milk’s protein is: 2.38 where as the literature value is 3.5, so my result is closer to the literature of the full fat milk, which has a value of 3.3. The literature value of lipids in skimmed milk is 0.3 where as my results are 0, which could be as the balance wouldn’t read the small amount, but my value is considerably closer to the literature value of skimmed milk then that of the others. My results been lower than that of the literature values could be caused by both procedural error and percentage error of my equipment. Taking this into account I am able to compare the unknown milk to the literature values and decide that the unknown milk is semi-skimmed milk. I have decided this as even though the lipid values of the unknown milk is nearest to the literature values of skimmed, it is slightly larger, and as within the experiment we were likely to loose material, meaning that the value of the protein is too high, and the protein value is also a lower value. Even though the value of the protein for full fat is near to that of the unknown milk, the lipid value is too different. Meaning the unknown sample is likely to be semi-skimmed milk.
