Determination of Dissolved Oxygen in Water Using the Winkler Method
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Water Resources In Egypt: Future Challeges and Opportunities
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Kolhapur city is one of the major cities in Maharashtra and well source of water bodies available in the western region of Maharashtra. But still facing the water scarcity in summer days due to the polluted water is unfit to use. Kolhapur district an
Quality of Water Level- B.E. Course - Civil Engineering
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Physico “Chemical analysis of surface and well water samples collected from eight sampling stations in the vicinity of Anandapuram, Visakhapatnam Dt. for three months during February to April 2017. The analysis consists of parameters such as pH, tota
Experiment 5
Analysis of Phosphate in Water General Discussion In the present experiment, we will analyze a series of natural water samples for their phosphate content. Detergents are among the greatest contributors to phosphate content in rivers and lakes because phosphate containing compounds are used in detergent formulation as water softeners (builders). Phosphate is not toxic to animals or plants. In fact, it is a plant nutrient which stimulates the growth of aquatic Weeds and algae. This may cause lakes and rivers to become clogged and overrun with plants. The principle of this method involves the formation of molybdophosphoric acid, which is reduced to the intensely colored complex, molybdenum blue. This analytical method is extremely sensitive and is reliable down to concentrations below 0.1 mg phosphorus per liter. Apparatus The Spectronic 20spectrophotometer will be employed in the measurement of color intensity of the blue solutions. A wavelength of 650 nanometers will be used in these analyses. Reagents a.
Ammonium molybdate reagent: (prepared reagent: (prepared by instructor) The solution is prepared
by dissolving 25g of (NH4)6Mo7O24·4H2O in 175 mL purified water. Cautiously, 280 mL of concentrated H2SO4 is added to 400 mL of purified water. The acid solution is cooled, the molybdate solution is added, and the entire mixture is diluted to 1 liter. b.
Stannous chloride reagent: (prepared reagent: (prepared by instructor) 2.5 g of SnCl2•2H2O is dissolved in 100 mL of glycerine. The mixture is gently heated to hasten dissolution.
c. Stock 20.0 mg/L phosphate solution: (prepared solution: (prepared by instructor) To prepare this solution, 0.286 g of KH2PO4 is dissolved in 1.0 liter of water. This is a 200 mg/L stock solution. Then dilute 100 mL of this solution to 1.0 liter. Then dilute 100 mL of this solution to 1.0 liter. Then dilute 100 mL of this solution to 1.0 liter. Procedure Note: Glassware should be washed thoroughly with hot water followed by rinsing with purified water. Do not use phosphatecontaining detergents to clean equipment for this experiment.
Prepare the following standard phosphate solutions: a.
1.0 mg/L standard: Place 2.00 mL of 20.0 mg/L phosphate solution in a 100-mL graduated cylinder and dilute to 40 mL with purified water. (Save exactly 25 mL in an erlenmeyer flask for analysis with the spectrophotometer.)
b.
2.0 mg/L standard: Place 4.00 mL of 20.0 mg/L phosphate solution in a 100-mL graduated cylinder and dilute to 40 mL with purified water. (Save exactly 25 mL in an erlenmeyer flask for analysis with the spectrophotometer.)
c.
3.0 mg/L standard: Repeat the directions for the 1.0 mg/L standard using 6.00 mL of 20.0 mg/L phosphate. (Save 25 mL)
d.
4.0 mg/L standard: Repeat the directions for the 1.0 mg/L standard using 8.00 mL of 20.0 mg/L phosphate. (Save 25 mL)
e.
5.0 mg/L standard: Repeat the directions for the 1.0 mg/L standard using 10.00 mL of 20.0 mg/L phosphate. (Save 25mL)
f.
Blank: Set aside 25 mL of purified water which will be treated with the color
developing reagent to serve as a blank. These five standard solutions and the blank should now be treated according to the following "color development" procedure. After measuring the absorbance of these solutions, make a plot of absorbance versus concentration as described by your instructor. Color development in sample: This procedure is used for the five standard solutions and for any river, lake, or sewage water samples
which are to be analyzed for phosphate.
Place in an erlenmeyer flask 25 mL of the water sample to be analyzed. Put 1.00 mL (using a pipet) of ammonium molybdate solution into the flask and swirl to mix. To the flask add 2 drops of stannous chloride solution and mix by swirling. If phosphate is present, a blue color will develop to a maximum in 5 minutes. Note: The time period is somewhat critical. Measurements should be taken anywhere from 5 to 15 minutes after addition of stannous chloride. While you are waiting for the blue color to develop, set the wavelength to 650 nm on the spectrophotometer. Use the blank solution to set it to read zero absorbance. Using 650 nanometers wavelength, measure the absorbance (after 5-10 minutes color development) of the blue sample.* Waste Disposal All solutions may be rinsed down the drain with water.
Calculations From the concentration and the absorbance of the five standards and the blank, make a plot of absorbance as a function of concentration (a "standard curve" or "Beer's Law plot"). Use the plot and the absorbance of each river, lake, sewage, or unknown solution to determine the concentration in milligrams phosphate ion per liter (mg/L 3-
PO4 ) in that sample. We sometimes use concentration units of parts per million (ppm) synonymously with mg/L because 1.0 liter of water at room temperature weighs 1000 grams (to two significant figures). Thus 1.0 mg is one millionth of the weight of one liter. For the sake of consistency in this manual we use units of mg/L and related units such as µg/mL and µg/L. *Should one of your samples produce a very dark blue color which can not be read with the spectrophotometer, dilute the original water sample 100 fold. This is accomplished by placing 1.0 mL of the water sample in a 100-mL graduated cylinder and then adding enough purified water to bring the volume up to 100 mL. Now 25 mL of this diluted sample may be analyzed according to directions for color development in sample, previously given. Remember that the concentration which you ultimately obtain from this sample will have to be multiplied by 100 because of the 100 fold dilution.
Report the following data: Sources of Water Samples 1. 2. 3. 4.
Absorbance of Standards: Blank 3-
1.0 mg/L PO4
3-
2.0 mg/L PO4
3-
3.0 mg/L PO4
3-
4.0 mg/L PO4
3-
5.0 mg/L PO4 Note:
Prepare a standard curve and turn it in with the report sheet.
Absorbance of Water Samples
Dilution Factor (if any)
1. 2. 3. 4.
Concentration of Phosphate in Water Samples 1.
3
2.
4
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Discussion Identify those aspects of the procedure which may have introduced some error into the final results. In each case indicate whether the error would cause the measured value to be too high, too low, or either.
