CHEMISTRY LAB ABSTRACT

A. Student

CH 227

6/23/17

Experiment 5: Determination of Phosphate in Water (Example of proper abstract)

Phosphates in surface water have been implicated in accelerating eutrophication of bodies of water.1 Phosphates enter waterways from human and animal wastes, phosphate-rich bedrock, laundry, cleaning, and fertilizer runoff. If too much phosphate is present in water, algae and weeds may grow rapidly, choke the waterway, and consume large amounts of oxygen resulting in the death of fish and other aquatic species. The purpose of this experiment was to determine the phosphate content in a water sample collected from Lithia Park in Ashland, OR. According to Beer's Law, shown in Equation 1, the spectrophotometric absorbance of a species is directly proportional to the concentration of the species in solution.

A = abC

(1)

The absorbance of a series of six phosphate standard solutions, which ranged from 7 x 10-4 M to 1 x 10-5 M, was measured at 880 nm on a Spectrum SP-1105 spectrophotometer versus a blank and a line was fit to the absorbance vs concentration data. A sample of water obtained at the upper duck pond in Lithia Park, Ashland, OR on June 22, 2007 was prepared in the same way as the standard solutions and its absorbance was also determined. More detailed procedures may be found in the course lab manual.2 From the measured absorbance of the water sample (0.041 at 880 nm) and the equation of the best-fit line (y = 1439.5x+ 0.0334), the phosphate concentration of the water sample was calculated to be 5.7 x 10-6 mol/L or 0.57 parts per million (ppm). The quality of the reported phosphate concentration is dependent upon the quality of the absorbance measurements and concentrations of the standard solutions used to construct the calibration curve. Some scatter among the data is noted, although the scatter about the best-fit line appears to be random in nature, it is noted that the intercept (0.0314) differs significantly from the intercept of zero as predicted by Equation 1. The concentration of phosphate in the water sample (0.57 ppm) exceeds the United States Public Health Service standard of 0.3 mg phosphate/L as the maximum allowable amount for drinking water.3 This result is indicative of significant animal impact from the ducks that frequent the pond.

References

1. Brown, T. L.; LeMay, H. E., Jr.; Bursten, B. E.; Murphy, C. J. Chemistry: The Central Science, 11th ed.; Pearson; Upper Saddle River, NJ, 2009; p 754.

1. Determination of Phosphate in Water; General Chemistry Experiments: A Manual for Chemistry 204, 205, and 206, Department of Chemistry, Southern Oregon University: Ashland, OR, 2016; pp 25-28.

1. USGS NAQWA CIRC1136 Nutrients in Nation’s Waters. http://pubs.usge.gov/circ1136/circ1136.html (Accessed June 16, 2011)