Gravimetric Determination of Moisture in Fertilizer Samples

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GRAVIMETRIC DETERMINATION OF MOISTURE IN FERTILIZER SAMPLES

J.P. FERRERIA
DEPARTMENT OF COMPUTER SCIENCE, COLLEGE OF ENGINEERING
DATE PERFORMED: DECEMBER 6, 2012

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RESULTS AND DISCUSSION

In this experiment, we demonstrated the process called gravimetric analysis, where we, specifically, measured the amount of moisture in a fertilizer sample. Here, the weights of the crucibles with the fertilizer samples are measured before and after placing them in the oven. The weights obtained are subtracted to get the amount of water adsorbed in a certain sample of the fertilizer.

First, the crucibles were washed to remove any other adhering compounds. Then, they were dried by being put inside an oven at a temperature slightly above the boiling point of water, 110ºC. Other methods for drying are available such as infrared drying, halogen drying and microwave drying, but the drying oven was used because it is the most accessible, and multiple samples can be determined at once. The weights were then measured after letting the crucibles dry and cool in a desiccator. Multiple weighings are required as a constant weight is needed, where the difference between two consecutive weighings is ±0.0003 grams. The ±0.0003 constant weight allowance was set because the heat from the slightly hot crucible reacts with the very sensitive analytical balance and would therefore cause some errors. This is also why the crucibles have to be cooled in a desiccator before being weighed. A constant weight is required to minimize the errors from natural factors like air humidity. Shown below is the table of values that our group obtained for the weights of the crucibles:

Table I. Table of Values for the Crucible Weights Trial No. | Crucible weight (g) | 1 | 33.0643 ± 0.0002 | 2 | 33.0639 ± 0.0002 | 3 | 33.0648 ± 0.0002 | 4 | 33.0645 ± 0.0002 | Constant Weight | 33.0645 ± 0.0002 |

After obtaining a constant weight for the



References: [1] Institute of Chemistry (2007) Analytical Chemistry Laboratory Manual [2] Gravimetric Analysis (2012, 26 December) Retrieved January 6, 2013 from http://en.wikipedia.org/wiki/Gravimetric_analysis [3] WEIGHING BY DIFFERENCE (n.d.), Retrieved January 6, 2013 from http://www.chemistry.mtu.edu/~djchesne/classes/ch2212/Experiments/balex.htm [4] Mettler-Toledo (2002), Methods of Moisture Content Determination, Halogen Moisture Analyzer from METTLER TOLEDO, Retrieved January 6, 2013 from http://www.northshorecare.com/pdf/moisture-methods.pdf [5] Determination of Moisture in Fertilizers (n.d.), Retrieved January 6, 2013 from http://www.fertilizer.org/ifa/content/download/53893/786540/version/1/file/2011_WGMH_new_orleans_Moisture_determination_draft_recommendation.pdf

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