Practical 2: Chemical treatment for potable water supplyIntroduction:The conventional treatment of water for potable (drinking) supply generally involves the use of chemicals to improve water quality. This is to ensure that the water is safe to drink and to ensure acceptable aesthetic quality. Some chemicals may be added to address public health needs, such as the addition of fluoride and other chemicals may be added to reduce the corrosiveness of water in the distribution system, e.g. the pH is controlled at neutral (pH 7) level by addition of lime.The use of some chemicals contributes to the water being safe to drink, as well as improving the aesthetic quality of water. In this practical, you will investigate the application of a coagulant, Alum (aluminium sulphate- Al2(SO4)3:18H20), to treat raw water that contains organics, imparts colour, contains suspended solids (turbidity) and inorganic compounds.Materials and Methods:Chemicals and equipment: Alum (5,000 ppm as Al2 (SO4)3:18H20); pH meter, raw water sample, burette, 100 mL beakers, magnetic stirrer device, magnetic flea, safety glasses, latex gloves, stop watch.Procedure: 1. Put on laboratory coat and safety glasses. 2. Pour 500 mL of water into a 1 litre glass beaker, place a magnetic flea into the beaker and place the beaker on the magnetic stirrer. 3. Measure the pH of the water sample. Ensure the pH meter is measuring accurately using the two pH standards provided. Rinse probe between tests. 4. Pour 40 mL of alum solution into a 100 mL beaker and carefully fill the burette. Place the burette outlet over the sample using the stand and clamps provided. 5. Switch on the magnetic stirrer to agitate the water rigorously and add 2.5 mL of alum solution. Stir rigorously for 2 minutes and then reduce the stirrer speed to slow speed. Continue slow stirring of the sample for 13 minutes and measure the pH. Record your observations. 6. After slow stirring, carefully pour about 100 mL of the water sample into a 125 mL beaker. After 10 minutes record your observations, including the clarity of the supernatant solution. Proceed with the next titration during this time. 7. Carefully fill a 1 cm quartz cuvette with the supernatant from the 125 mL beaker that has been standing undisturbed for 10 minutes. Note that filtration may be required; however your demonstrator will advise this. Measure the UV absorbance at 254 nm using a spectrophotometer as shown by your demonstrator. Also measure the absorbance of the treated sample at 456 nm in a 5 cm glass cuvette using the other spectrophotometer available. 8. Repeat the above using 5 mL, 10 mL and 15 mL of alum, with new water samples for each test and also measure the absorbance and colour of the raw water sample prior to any treatment with alum.Note: Colour in Hazen Units (HU) is determined from a one-point calibration, where 50 HU is equal to 0.070 O.D. absorbance at 456 nm - using a 5 cm glass cuvette.Report: In your report, address the following questions and tasks:No. 1. Prepare a table of the following data: Raw water sample, sample volume used, coagulant volume used, coagulant dose (mg L-1), UV absorbance, colour.No. 2. Draw graphs of UV absorbance vs alum dose, Colour vs alum dose, pH vs alum dose.No. 3. Discuss the selection of an alum dose for this water sample, based on the alum treated water qualities.No. 4. Which dose might be best based on the aesthetic water quality. Discuss.No. 5. Which dose might be best based on the safety considerations of this water. Discuss.No. 6. In the coagulation process, have all the UV absorbing compounds been removed? What percentages remain after alum treatment? What does the presence of UV absorbing compounds before and after alum treatment infer?No. 7. Calculate the ratios of Colour (HU)/UV and compare the ratios of the raw with the treated waters. Discuss the significance of these ratios.No. 8. Discuss your observations of the changes in the clarity of the water before and after treatment.No. 9. Write a report in the format of Title, authors, abstract, introduction, materials and methods (refer to the practical manual and detail any changes adopted), results and discussion, conclusions and references. (Answer all questions).