Gravimetric Analysis Of The % Phosphorous In Miracle Gro

The purpose of this experiment was to analyze the % phosphorous in Miracle Gro. Gravimetric Analysis was used to determine the content of phosphorous in this water soluble fertilizer. The overall goal of Gravimetric Analysis is to form the precipitate MgNH4PO46H2O and isolate it from the aqueous solution by vacuum filtration. In order to obtain the precipitate, a series of dissolution reactions and vacuum filtration were performed. First, Miracle Gro was dissolved with DI water and reacted with activated copper to remove coppers ions in the fertilizer. After copper ions were filtered, approximately 15mL of .5M was added to the filtrate, which made the mixture acidic. Then, 20 mL was added into the filtrate to raise the pH of the mixture.

The black dots are sign of unfiltered activated carbon, which reduce the accuracy of the % phosphorous in the Miracle Gro. This contamination is a systemic error. Since the mass activated carbon are included in the mass of precipitate, the accuracy of phosphorous in the Miracle Gro is not accurate. This impurity is due to contamination when performing the vacuum filtration step. When the activated copper was filtered the first time, the filtrate was still blue. More activated copper was added to the filtrate and vacuum filtration was perform again. The error arrived when the filter paper was not replaced because there might have been a hole inside the paper that prevents all the activated carbon to be filter. Since the paper was pitch black, it was impossible to see if there is leakage. The filtrate was less blue after the second filtration. A third vacuum filtration was performed after adding much more activated carbon. Since the experiment procedure did not specify how much activated carbon should be added, too much activated carbon was added. This can lead to systemic errors because there was so much activated carbon on the top of funnel that won’t even wash off, which might had came back as contaminates

This was probably heat generated from the reactions of and the mixture to generate the precipitate. The precipitate was filtered out once, but the filtrate was not colorless, but still milky white. The white milky filtrate indicates the presence of . The filtrate was not reused, so some of precipitate may have been lost. There may have been some other contaminations in the funnel or filter paper that contributed to this color. Possibly, there might been some precipitate in the precipitation flask, but was not rinse with acetone and re-filter due to lack of time. For future practices, DI water should be added at reasonable proportions and not too much on precipitate that won’t wash out. This will make the vacuum filtration a quicker process by avoiding large volume of filtrate. Moreover, the filter paper should be replaced after a new vacuum