Gravimetric Analysis Lab

The purpose of this lab was to practice the skill of gravimetric analysis to determine the concentration of an analyte in a solution. The objective of this lab was to determine the amount of phosphorus in a sample of plant food compare that to the amount labeled on the container, which was 30%. In order to get the mass of phosphorus by itself, 2.5 grams of 10% liquid MgSO4 and 25 mL of ammonium was mixed with the liquefied form of the plant food in order to create a precipitant. This precipitate was the analyte that was needed to be extracted from the solution. After waiting 45 minutes for the phosphorus to settle to the bottom, the solution was filtered through a filtering paper and excess water was collected in the cup. When filtration was

Compared that to the reported amount, there was only a 1.3% error, while the class had an average error of 6.35%. These results are quite impressive because the percent errors were quite low for a high school lab. Errors could have occurred during this lab that would have affected the accuracy of the gravimetric analysis. Some errors could include not waiting for a complete filtration of the solution which could have led to a decrease in phosphorous collected or a spill could have occurred. During the last filtration process, it was highly possible that a lost of product could have occurred if the precipitate was able to flow through the filtration paper. In order to prevent this in future investigations, a better filtration paper could be used or the excess water collected in the cup could be refiltered to collect any extra analyte that seeped through. Although the result collected from our group was very close to the reported amount, averaging the result helped other groups who had a high percent error, such as 12%, get a closer mass value and percentage of