Vitamin Water Experiment

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For this experiment the amount of zinc in vitamin water had to be determined. To do this, three methods were applied. The first was by a calibration plot method, where zinc standards were prepared and from the absorbance of those standards a calibration curve was plotted, which in turn was used to determine the amount of zinc in vitamin water.
The second method was standard addition. For this method, an un-spiked and spiked solution were prepared. The un-spiked solution only contained the vitamin water, while the spiked contained the vitamin water and a standard zinc spike. From the absorbance of those solutions, the amount of zinc in vitamin water was determined using the standard addition formula:[X]i/([S]f+[X]f)=Ix/(Is+x)
The third
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In the second method it was 0.86 ppm and in the third 7.31 ppm. Comparing these data, we see that the concentrations using the different methods, do differ a lot from one another. One of the reasons for this huge difference, was the use of a serological pipette instead of volumetric pipettes. For all transfer of solutions where a pipette was needed, a serological pipette was used. Now this could be one of the main causes of error in the data, because a serological pipette is not accurate, however a volumetric pipette is. This mistake may have also caused a correlation coefficient that’s not close to 1 or -1. And the concentration of zinc in method 2 differs a lot from the ones calculated for method 1 and 3 because a mistake was made here. Instead of using the vitamin water that was prepared for the un-spiked solution, the vitamin water that was filtered was used. This caused a huge error in the zinc concentration …show more content…
The 3 methods were calibration plot method, standard addition and standard addition by graphic procedure. The 3 methods are generally good methods to determine the amount of an analyte in sample. But there were a couple huge mistakes made in this experiment. The first was, using a serological pipette instead of volumetric pipettes. Serological pipettes are not as accurate as volumetric pipettes, and will not deliver exactly the same volume as indicated. The other mistake was, using the wrong vitamin water. The diluted vitamin water that was made for the un-spiked solution was supposed to be used, instead the mistake was made of using the filtered vitamin water. From these mistakes we cannot conclude precisely which method was best, but looking at the data we see that from the first and third method we get the most precise data for the zinc concentration in vitamin water. In the first method the zinc concentration was 6.025 ppm and in the third it was 7.31 ppm, however in the second it was 0.86

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