Lab Procedure

SAFETY NOTES:

Part 1: Collection of Samples
	You will be collecting your own water sample for use in this laboratory. The collection should take place no more than 24 hours before lab. This is because analysis must take place within 48 hours to be valid. The sample should come from a fresh water source because there are specialized tests required to analyze salt water samples that we are not equipped to run.
	Obtain a clean and dry ~1L glass or plastic bottle. You may use a 20 oz + soda bottle if you clean it thoroughly with hot water and rinse it with vinegar. Do not use soap as this might add phosphate.
	Find a source of fresh water. Make copious notes regarding the location and condition of the source. Collect the sample by inserting the bottle upside-down into the water. Rotate the open end toward the direction of the flow, and allow the bottle to fill under the surface. Sample about 12 inches under the surface. Avoid surface scum and bottom sediment.
	Label the bottle with the sample name, location and time collected and the initials of who collected the sample. Store in a refrigerator until time for lab. (You can bring samples by the lab early in the day or keep them on ice in a small cooler until lab.)
Part 2: Analysis of pH
	Take 50 mL of your water sample and place it in 100 mL beaker that has been cleaned and rinsed with the acid wash and distilled water provided.
	Using the Orion® pH meter, take the pH of the sample and record it in your notebook (See the Appendix for Orion® pH meter instructions if needed).
Part 3: Analysis of PO₄^3-
	Turn on your spectrometer.
	Take 25.0 mL of your water sample, 25.0 mL of stock phosphate solution and 25.0 mL of distilled water and place each of them in separate 100 mL beakers that have been cleaned and rinsed with the acid wash provided.
	To the beakers containing the unknown water samples (one from each student at the bench) and to the phosphate standard beaker (only one which is shared) add 1 mL of the Ammonium Molybdate color reagent and 2 drops of stannous chloride.
	Mix the solutions for 5 minutes, allowing color to develop.
	Using the calculations from your prelab, create the four serial dilutions of your stock solution. These will be used to create the standard calibration graph to determine the concentration of your unknown so be meticulous in your technique when making the dilutions.
	*You are now ready to measure the absorbance of your samples.* Make sure your spectrometer has been on for a minimum of 10 minutes. Obtain a cuvette from the TA. Be responsible for it and return it at the end of the class.
	Wash the cuvette carefully and rinse with distilled water. Do not use brushes to wash the cuvettes, as they scratch very easily. Fill one of the cuvettes to about two-thirds (2/3) full with your distilled water blank.
	Press the A/T/C button on the spectrometer to select the absorbance mode. The current mode appears on the display.
	Using the nm (up/down) controls, set the wavelength at 543 nm.
	Insert the blank cuvette into the sample compartment and close the compartment’s lid. Observe the white reference mark on the cuvette. Align this mark with the one on the sample compartment every time a measurement is taken.
	Press 0 ABS/100%T to set the blank to 0 absorbance. Remove the “blank” cuvette and discard the blank water sample.
	Rinse the sample cuvette with a small portion of the standard stock solution (2.50g/L) and discard the rinse. Fill the cuvette to about 2/3 with the stock solution and insert into the sample compartment. Record the absorbance.
	Remove the sample cuvette, discard the stock solution in the waste jar and rinse the cuvette well with DI water. Rinse the sample cuvette again with a small portion of the your next standard solution and discard the rinse. Fill the cuvette to about 2/3 with the standard solution and insert into the sample compartment. Record the absorbance. Repeat until all the standards and all of the student’s unknown samples have been measured.
Part 4:Water Purification (Each student should purify their own water sample.)
	*Using the 100 mL of your water sample. Slowly* filter the sample using a suction filtration set-up to remove large particulates. Use 0.1 mm filter paper. After a liquid sample has been passed through a filtration system it should now be called a “filtrate”.**
	Add 1 spatula of dry lime (CaO) powder and 1 spatula of dry alum (Al₂SO₄) powder to the filtrate and stir with a clean, glass stirring rod. Allow the powders to react for ~10 minutes. Make observations.
	Using your filter funnel again, place a filter paper in the funnel and then add enough sand to cover the filter paper with ~.5cm of sand. Pass the filtrate through the sand slowly.
	Add 1 mL of sodium hypochlorite reagent to the filtrate. Stir to mix completely.
	Set up the charcoal filtration funnel. Place a filter paper in the Buchner funnel. Add a 1 cm layer of activated charcoal on the filter and then cover with a second filter. Attach a hose to the side nozzle of the water faucet in the sink and the side nozzle of a filtration flask. Use an adaptor and fit the funnel into the flask. Rinse the charcoal with distilled water until the water in the flask is clear. Make sure you discard the charcoal rinse water and dry the filtration flask before filtering your water sample. Pass your water sample through the fully rinsed charcoal filter. Make observations regarding color and clarity of the “purified” water.
Part 5: Water Quality After Purification
	Repeat the pH and phosphate test for your "purified" water sample only. You don’t need to repeat the measurement for the standards.