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EXPERIMENT 25:

The Fertilizer Project – Analysis of Phosphorus in Fertilizer

The Significance of Phosphate Phosphorus is necessary for many of life’s processes to take place. It is present in compounds such as DNA and ATP (adenosine tri-phosphate) which most cells cannot live without. In fact, “phosphorus is often a limiting nutrient in many environments.”1 Due to this fact, it is of particular environmental significance the world round. Phosphates are used as one of the main ingredients in fertilizers and are extracted by many plants from the soil through the help of phosphate transfer proteins.2 Under normal conditions it is difficult for plants to get easily usable phosphate directly from the soil; it is usually lacking in soil due to over use or is present as inorganic phosphorus and must be converted—by bacteria or the plant itself—before use.3 Fertilizers allow plants ready access to vast amounts of water-soluble phosphates, potash and nitrogen all of which aid in promoting enhanced plant growth.4 While water soluble phosphate use is a boon to the agriculture side of things, making sure that the amounts in the system are within a normal range is also a concern. Phosphorus does not have a gaseous form under the climate conditions usually found on earth, which means that it can build up and cause more harm than good if proper levels are not maintained. This becomes especially problematic after fertilizers have been used and the water soluble ions are swept into rivers and lakes.5 Efforts are being made to find a solution to this problem, but a clearly sustainable answer does not yet seem apparent. In the not so distant past, little or nothing was done to limit the problem of fluoride pollution which was caused during the industrial process of producing fertilizer. Now, there are steps in place to limit the release of these compounds into the 1

http://en.wikipedia.org/wiki/Phosphorus http://uc.library.ingentaconnect.com/content/klu/plso/2003/00000248/F0020001/05094403?crawler=true 3 http://www.idrc.ca/en/ev-5458-201-1-DO_TOPIC.html 4 http://www.thegardenhelper.com/fertilizer.html 5 http://www.ext.colostate.edu/ptlk/1620.html 2

environment.6 Hopefully this will also happen and a solution to the water shed problem will be found. Phosphates are very significant when one looks at the operations of the environment, but it impacts so many processes which are constantly occurring each day that it would be impossible to describe them all here. Above an attempt has been made to touch on some of the most important systems affected, both for humanity and science as a whole.

6

http://fluoridealert.org/phosphate/overview.htm

Introduction The purpose of this experiment was to investigate the phosphorus content of soluble fertilizer and get a team of four people to do the experiment. Each team was required to develop two protocols; The concepts of concentration, absorbance, volume of solution, and calibration curve are related to the material covered in the Chemistry 101 and 102 lectures. I was able to use some of the laboratory techniques I did in previous experiments involving calibration curves.

Experimental Procedure The procedure was given in the Laboratory Experiments for First Year Chemistry; Fifth Edition 2006;

Results The summary of the experimental data is given and attached in the end of this report. Also see the calculation page at the end of this lab report.

Overall Conclusion and Error Discussion The gravimetric method is less accurate than the spectrometric method. In the gravimetric method we are required to transfer the solid collected after filtration and make sure the entire solid is transferred to the watch glass; however, the watch glass is shallow and any material spills causes the results to be lower than expected. Drying the solid took a long time and I was never really sure if the solid was completely dry. The procedure and calculations for this method are

easier than the spectrometer method; however, exact measurements are required for this method (See calculation page at the end of this lab report). Although the group average was good related to the expected value, the precision part of the experiment was somewhat limited. Although we have the same protocol to follow, the measurement made during the experiment was not standardized. For example, we did not standardize the way to read the pipette during the experiment or the time for the solid collected in the gravimetric method to dry; therefore, our result present inaccurate precision. The spectrometric method is more complex than the gravimetric method, but it provides a more accurate value than the Gravimetric method. This is because the chances of spilling the liquid after filtration are remote. More calculations are required for this method (See calculation page at the end of this lab report). Considering the overall result, the spectrometric method is better for the analysis of phosphorus in fertilizer because it provides more accurate results and less room for error. Our average percent of P2O5 was 22.17 % in the Gravimetric Method and 23.49% in the spectrometric method when the expected result was 24.00%. . Questions (pp. 25-6 to 25-10)  If the beaker is not dry it would affect the concentration of the fertilizer or KH2PO4.  The original sample must be dry since any unknown amount of water in the sample will contribute to the original weight taken by making it heavier than it actually is.  The exact volume will not make a difference because it will evaporate and we are interested in the precipitate.  The precipitate will get lighter because the water and the alcohol will evaporate.

 The insoluble substance will affect the result by adding to the final sample weight making it heavier.

Table 1: Summary of KH2PO4 Analysis Data for Gravimetric Method Name KH2PO4 Mass of Sample Trial 1 Trial 2 Mass of Mg(NH4)PO4 x 6H2O Trial 1 Trial 2 Mass of P in Mg(NH4)PO4 x 6H2O Trial 1 Trial 2

.444 g .444 g

.414 g .441 g

.720 g .735 g

.724 g .760 g

.0908 g .0927 g

.0913 g .0959 g

%P2O5 in Sample Trial 1 Trial 2 Average Group Average

46.87% 47.86% 47.36% 47.84%

47.14% 49.48% 48.31% 47.84%

Expected % P2O5

52%

52%

Table 1.1: Summary of Fertilizer Analysis Data for Gravimetric Method Name Fertilizer Mass of Sample Trial 1 Trial 2 Mass of Mg(NH4)PO4 x 6H2O Trial 1 Trial 2 Mass of P in Mg(NH4)PO4 x 6H2O Trial 1 Trial 2

.962 g .963 g

.933 g .919 g

.965 g .955 g

.964 g .963 g

.773 g .745 g

.685 g .637 g

.764 g .704 g

.801 g .790 g

.0925 g .0940 g

.0864 g .0804 g

.0963 g .0888 g

.101 g .099 g

%P2O5 in sample Trial 1 Trial 2 Average Group Average

22.02% 22.34% 22.17% 22.17%

21.22% 20.03% 20.62% 22.17%

22.90% 21.30% 22.13% 22.17%

23.80% 23.70% 23.75% 22.17%

Expected %P2O5

24%

24%

24%

24%

Table 2: Calibration Curve for the Spectrometric Method Concentration of (PO4)3 - stock solution = 5.00*10-3 M (PO4)3Volume of Working Solution (ml) Concentration of P in 10ml flask 5 4 3 2 1

ml ml ml ml ml

3.0 2.4 1.8 1.2 6.00

x x x x x

Absorbance

10^-5 10^-5 10^-5 10^-5 10^-6

0.653 0.547 0.472 0.320 0.154

Table 3: Summary of Fertilizer Analysis Data for Spectrophotometric Method Fertilizer g of fertilizer Absorbance of 5 ml solution 4 ml solution 3 ml solution 2 ml solution 1 ml solution M of P in

.2992 g

.2992 g

.2810g

.2992 g

.538 g .378 g

.511 g .422 g

.745 g .659 g

.214 g .352 g

.303 g .206 g .118 g

.386 g .288 g .189 g

.598 g .231 g .092 g

.540 g .631 g 1.223 g

5 ml solution 4 ml solution 3 ml solution 2 ml solution 1 ml solution g of P from Fertilizer %P2O5 from Fertilizer Group % Average Expected % P2O5

1.88 x 10-5 1.32 x 10-5 1.08 x 10-5 7.22 x 10-6 4.13 x 10-6

1.78 x 10-5 1.4781 x 10-5 1.3520 x 10-5 1.0087 x 10-5 6.6199 x 10-6

3.71 x 10-5

5.26 x 10-5

2.84 x 10-5

2.72 x 10-5

2.57 x 10-5

2.32 x 10-5

9.94 x 10-6

1.52 x 10-5

3.96 x 10-6

9.21 x 10-6

.0237 g

.0302 g

.0413 g

.116 g

18.12% 23.49%

23.17% 23.49%

14.70% 23.49%

38% 23.49%

24%

24%

24%

24%...