The purpose should include a majority of the topics and techniques covered in the experiment. The procedure section must cite the lab manual and include the location, date, and time of sample collection. Also be sure to note any changes made to the procedure.

The data section should include a data table with the phosphate concentrations and absorbance values of the 5 standard solutions and your water sample before and after purification. The concentration of phosphate in your water sample before and after purification should be reported BOTH in ppm and molarity. [ 1ppm = 1mg/L; 1 mole PO₄^-3 = 9.5 x 10⁴ mg PO₄^-3] The pH of the water sample before and after purification must also be reported. Lastly include all observations of your water sample made before and after purification. (These must match those of your lab notebook or it will be considered cheating.)

For the calculation section prepare a concentration vs. absorbance graph for PO₄^-3. (This is made using the serial dilutions/standard solution values.) All graphing guidelines apply here. Sample calculations of the concentration of the water sample before and after purification using BOTH methods: The equation of the line, plugging in y (the absorbance) and solving for x (the concentration) and using Beer’s Law (A=ebc, where A is the absorbance, e is the molar absorptivity which is equal to the slope of the line, b is 1.00 cm and c is the concentration (what you are solving for.)) Also include the conversion from ppm to molarity. Lastly you must include an example calculation of the purity of the water sample. This can be determined using the following formula.

 

The conclusion should be several paragraphs addressing the following: The location where the water sample was obtained, the anion concentration and pH of the water sample before and after purification. An explanation of the anion concentration level and pH value of the water sample before and after; in other words what might be causing these values. A discussion on how "pure" your water sample was before purification. Lastly, discuss any possible errors in the experiment.

Answer the following questions:

1. Why should we care about the amount of PO₄^3- found in a natural water source?


2. If you really wanted to be sure your water was drinkable, what further purification step(s) would you take?


3. Blue light has a wavelength between 450-495 nm. Why don't we measure the absorbance of a blue solution within this wavelength range?