ADVANCED LEARNING PACKAGES WATER QUALITY AND WATER TREATMENT

Transcription

1 ADVANCED LEARNING PACKAGES MICROSCIENCE ENVIRONMENTAL EXPERIMENTS WATER QUALITY AND WATER TREATMENT SC/BES/MCS/2006/10 December 2006 Original: English Manual for Learners - First Edition Compiled by Beverly Bell, Bina Akoobhai et al. Edited by Prof. JD Bradley 2006 RADMASTE Centre µscience United Nations Educational, Scientific and Cultural Organization The UNESCO-Associated Centre for Microscience Experiments, RADMASTE Centre

2 Prepared under UNESCO Contract No This Booklet of Environmental Microscience Experiments has been Prepared in Cooperation with UNESCO, IOCD and IUPAC UNITED NATIONS EDUCATIONAL, SCIENTIFIC AND CULTURAL ORGANIZATION INTERNATIONAL ORGANIZATION FOR CHEMICAL SCIENCES IN DEVELOPMENT INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY IUPAC IN COLLABORATION WITH µscience THE UNESCO-ASSOCIATED CENTRE FOR MICROSCIENCE EXPERIMENTS THE RADMASTE CENTRE UNIVERSITY OF THE WITWATERSRAND JOHANNESBURG, SOUTH AFRICA THE INTERNATIONAL FOUNDATION FOR SCIENCE EDUCATION JOHANNESBURG, SOUTH AFRICA SESI SCIENCE EDUCATION SOLUTIONS INTERNATIONAL P.O. BOX 681, WITS 2050, JOHANNESBURG, SOUTH AFRICA

3 Worksheets Prepared By : Ms B. Bell & Ms B. Akoobhai, et al (UNESCO-Associated Centre for Microscience Experiments, The RADMASTE Centre, University of the Witwatersrand) µscience Worksheets Edited By : Prof. J. Bradley (International Foundation for Science Education)

4 ADVANCED LEARNING PACKAGES MICROSCIENCE ENVIRONMENTAL EXPERIMENTS WATER QUALITY AND WATER TREATMENT CHAPTER SOURCES OF SUBSTANCES IN WATER...5 ACTION OF SOAPS AND DETERGENTS...7 EUTROPHICATION...8 INDUSTRIAL POLLUTION (SULPHUR DIOXIDE)...9 FACTORS INFLUENCING WATER POLLUTION BY AIR POLLUTANTS...11 PART 1 WHAT IS THE FUNCTION OF A CHIMNEY IN AN INDUSTRIAL PLANT WHICH EMITS AIR POLLUTANTS? PART 2 CAN THE EMISSION OF AIR POLLUTANTS FROM AN INDUSTRIAL PLANT BE ELIMINATED? SOLUBILITY OF GASES IN WATER...13 Part 1: PREPARATION OF SULPHUR DIOXIDE Part 2: PREPARATION OF CARBON DIOXIDE Part 3: PREPARATION OF OXYGEN Part 4: PREPARATION OF NITROGEN CHAPTER WATER TESTING...16 THE TEST FOR DISSOLVED OXYGEN...18 PART 1: HOW CAN WE TEST FOR DISSOLVED OXYGEN IN WATER? PART 2: WHAT IS THE EFFECT OF TEMPERATURE ON THE CONCENTRATION OF DISSOLVED OXYGEN IN WATER? TESTING FOR THE ACIDITY/BASICITY OF DRINKING WATER...21 THE TEST FOR NITRATE IN WATER...23 TESTING FOR PHOSPHATE IN DRINKING WATER...25 PART 1 DOES THE WATER SOURCE THAT YOU DRINK FROM HAVE AN ACCEPTABLE PHOSPHATE CONTENT? (SILVER NITRATE TEST) PART 2 DOES THE WATER SOURCE THAT YOU DRINK FROM HAVE AN ACCEPTABLE PHOSPHATE CONTENT? (AMMONIUM MOLYBDATE TEST) TESTING FOR THE PRESENCE OF HEAVY METAL IONS IN WATER...27 TESTING THE CONDUCTIVITY OF WATER...29 TESTING FOR HARDNESS IN WATER...31 CHAPTER WATER TREATMENT THE INDUSTRIAL PURIFICATION OF WATER: CHLORINATION...35 WATER SOFTENERS: WATER SOFTENERS:

5 CHAPTER 1 SOURCES OF SUBSTANCES IN WATER 5

6 SOURCES OF SUBSTANCES IN WATER ACTION OF SOAPS AND DETERGENTS EUTROPHICATION INDUSTRIAL POLLUTION (SULPHUR DIOXIDE) FACTORS INFLUENCING WATER POLLUTION BY AIR POLLUTANTS PART 1 WHAT IS THE FUNCTION OF A CHIMNEY IN AN INDUSTRIAL PLANT WHICH EMITS AIR POLLUTANTS? PART 2 CAN THE EMISSION OF AIR POLLUTANTS FROM AN INDUSTRIAL PLANT BE ELIMINATED? SOLUBILITY OF GASES IN WATER Part 1: PREPARATION OF SULPHUR DIOXIDE Part 2: PREPARATION OF CARBON DIOXIDE Part 3: PREPARATION OF OXYGEN Part 4: PREPARATION OF NITROGEN 6

7 SOURCES OF SUBSTANCES IN WATER ACTION OF SOAPS AND DETERGENTS Apparatus: Chemicals: 3 x propettes ; 1 x comboplate ; 2 x toothpicks. Tap water; cooking oil; dilute dishwashing liquid. 1. Half fill wells F1 and F2 with water using a clean propette. 2. Using a clean syringe add 5 drops of cooking oil to each of wells F1 and F2. (See Question 1) 3. With a clean propette add 10 drops of dilute dishwashing liquid to well F1. 4. Stir the solutions in wells F1 and F2 using clean toothpicks. (See Question 2) QUESTIONS Q1. What do you observe in wells F1 and F2? Q2. Describe what you observe in well F1. Q3. Explain why there is a difference in observation in wells F1 and F2. 7

8 SOURCES OF SUBSTANCES IN WATER EUTROPHICATION Apparatus: Chemicals: 1 x propette ; 2 x vials ; 1 x toothpick; 1 x microspatula, 1 x marking pen. Pond water (containing algae and plant material); Pentasodiumtriphosphate (Na 5 P 3 O 10 (s)). 1. Add pond water to both the vials using a clean propette, until each is ¾ full. Label one vial as vial 1 and the other as vial To vial 1 add 3 microspatulas of pentasodiumtriphosphate. Stir using a toothpick. 3. Place both the vials in a place with direct sunlight. Leave the vials undisturbed and observe any changes on a daily basis for 1 week. QUESTIONS Q1. What is the purpose of vial 2? Q2. Describe what you observe in vials 1 and 2 after 1, 3, 5, 7 days. Q3. Explain why there is a difference in observation in vials 1 and 2. Q4. What phenomena is occurring in vial 1? Explain in detail. 8

9 SOURCES OF SUBSTANCES IN WATER INDUSTRIAL POLLUTION (SULPHUR DIOXIDE) Focus Question: Does an industrial plant emitting sulphur dioxide acidify open water in its vicinity? Apparatus: Chemicals: 1 x comboplate ; 1 x lid 2; 1 x 2 ml syringe; 1 x plastic microspatula; 2 x propettes; 1 x plasticine. Hydrochloric acid (HCl(aq)) [5.5 M]; Anhydrous sodium sulphite powder (Na 2 SO 3 (s)); Tap water; Universal indicator solution. Introduction Air pollution has become a big problem in recent years. This experiment aims to simulate an industrial plant, which produces gaseous sulphur dioxide, and determine what factors influence the effect of the air-pollution on the water in the vicinity. The small wells of the comboplate, filled with water, will be used to represent the water supply. 1. Place the comboplate under a running water tap and fill all the small wells (wells A1 to D12) with water. 2. Use an empty propette to suck up, and then discard any water that may have got into the large wells. Use a paper towel to gently soak up any water between the small wells on the surface of the comboplate. 3. Use a propette to add one drop of universal indicator solution into each of the small wells filled with water. silicone tube connector vent 4. Using the spooned end of a plastic microspatula, add three spatulas of anhydrous sodium sulphite powder into well E3. Insert lid 2 (see figure above) into well E3 in such a way that the vent is closest to the small wells and the tube connector is pointed away from the small wells. 5. Seal the tube connector on lid 2 with a piece of plasticine (see the figure below). LID 2 water source (all small wells filled with water + universal indicator) pollution source (SO 2 (g) emitted from well E3) lid 2 with vent hole facing the small wells plasticine ball to seal tube connector on lid 2 If there are any draughts in the room, the results of the experiment may be affected slightly. If you like, you can use a shallow container such as an empty cardboard box to prevent the effect of any draughts on the experiment. This is, however, not a necessity. 6. Fill the syringe with 0,2 ml of 5.5 M hydrochloric acid. Hold the nozzle of the syringe just inside the vent in lid 2. Add all of the hydrochloric acid into well E3. Do not push the nozzle of the syringe all the way into the vent of lid 2, because the syringe will become stuck in the lid. Be careful not to drop any of the hydrochloric acid into the water. 7. Wait about three to five minutes. While waiting, answer the following questions. 9

10 INDUSTRIAL POLLUTION (SULPHUR DIOXIDE) QUESTIONS Q 1. What is the colour and ph of the aqueous solution of universal indicator at the beginning of the experiment? Q 2. Q 3. Q 4. What happens to the colour of the aqueous solution of universal indicator in the wells? What is happening to the ph of this solution? Explain your answer to question 2 using a chemical equation to represent the reaction that could be occurring. After about 1½ minutes of waiting, briefly lift the comboplate to the light and observe the colour of the aqueous solutions from underneath the comboplate. Does the colour of the aqueous solution change uniformly: a) across the surface area of the solution in each well, b) from top to bottom in each well? Q 5. Suggest a reason for your answer to question 4. Q 6. Q 7. Q 8. Q 9. Is the acidification of the solution the same throughout all the small wells of the comboplate? Explain your answer. In how many wells has the water been acidified? (Answer this no longer than 5 minutes from the time you began the experiment.) Would the number of wells showing water acidification be more or less if six microspatulas of sodium sulphite were added to well E3 instead of three, when the experiment began? Explain your answer. After counting the number of acidified wells, hold the comboplate to the light once again. How has the distribution of the acidification changed from the first time you viewed the wells from beneath the comboplate? Explain your answer. Q10. What is the answer to the focus question? Clean the comboplate thoroughly. EXTENSION QUESTIONS Q11. Use your answer to question 6 to explain why industrial areas are often located far away from residential areas. Q12. Adult fish can often survive in acidic water, but their eggs are killed by acidic conditions. Use your answer to question 9 to predict the effects of acid rain on populations of living organisms, like fish, over a prolonged period of time. Q13. During this experiment, the solutions in the small wells were not disturbed in any way. Use your answer to question 9 to explain why acid rain can have devastating effects on ecosystems located far downstream from an industry, which is built near a turbulent river. Q14. If the vent on lid 2 were sealed with plasticine and the tube connector was left open instead, predict whether the extent of acidification would increase or decrease if the experiment was repeated? Give a reason for your prediction. 10

11 SOURCES OF SUBSTANCES IN WATER FACTORS INFLUENCING WATER POLLUTION BY AIR POLLUTANTS PART 1 Focus Question 1: What is the function of a chimney in an industrial plant which emits air pollutants? Apparatus: 1 x 2 ml syringe; 2 x thin stemmed propettes; 1 x plastic microspatula; 1 x comboplate ; 1 x lid 1; 1 x piece of plasticine (5 mm x 5 mm x 5 mm); 1 x silicone tube (1.5 cm x 4 mm). Chemicals: Hydrochloric acid (HCl(aq)) [5.5 M]; Anhydrous sodium sulphite powder (Na 2 SO 3 (s)); Universal indicator solution; Tap water. 1. Place the comboplate under a running water tap and fill all the small wells (wells A1 to D12) with water. 2. Use an empty propette to suck up, and then discard any water that may have got into the large wells. Use a paper towel to gently soak up any water between the small wells on the surface of the comboplate. 3. Use a propette to add one drop of universal indicator solution into each of the small wells filled with water. 4. Using the spooned end of a plastic microspatula, add three spatulas of anhydrous sodium sulphite powder into well E3. Insert lid 1 (see figure alongside) into well E3 in such a way that the tube connector is closest to the small wells and the syringe inlet is pointed away from the small wells. 3. Fit the silicone tube over the tube connector on lid 1. This will model the chimney. The remainder of the steps may be performed in a draught-free area. 4. Fill the syringe with 0,2 ml of 5.5 M hydrochloric acid. Fit the syringe into the syringe inlet in lid 1. Add all of the 5.5 M hydrochloric acid gently into well E3. Do not add the acid too quickly as the increase in pressure in the well may force acid out through the silicone tube. Be careful not to drop any of the hydrochloric acid into the water. 5. Immediately after completing step 4, remove the syringe from lid 1 and seal the syringe inlet with a piece of plasticine. Be careful not to drop any of the hydrochloric acid into the water. pollution source (SO 2 (g) emitted from well E3) water source (all small wells filled with water + universal indicator) lid 1 with tube connector facing the small wells silicone tube connector silicone tube fitted over tube connector to model chimney plasticine ball to seal syringe inlet on lid 1 LID 1 syringe inlet 6. Wait about 3 to 5 minutes and observe. (See Questions 1, 2) Clean the comboplate thoroughly before proceeding with part 2. QUESTIONS Q1. Is the acidification of the solution the same throughout all the small wells of the comboplate? Explain your answer. Q2. In how many wells has the water been acidified? (Measure this no longer than 5 minutes from the time you began the experiment.) Q3. Is the number of wells showing water acidification greater or smaller when a chimney is present? Q4. What is the answer to focus question 1? 11

12 SOURCES OF SUBSTANCES IN WATER FACTORS INFLUENCING WATER POLLUTION BY AIR POLLUTANTS PART 2 Focus Question 2: Can the emission of air pollutants from an industrial plant be eliminated? Apparatus: 1 x 2 ml syringe; 3 x thin stemmed propettes; 2 x plastic microspatulas; 1 x comboplate ; 1 x lid 1; 1 x piece of plasticine (5 mm x 5 mm x 5 mm); 1 x silicone tube (1.5 cm x 4 mm); 1 x piece of cotton wool (3 mm x 3 mm). Chemicals: Hydrochloric acid (HCl(aq)) [5.5 M]; Anhydrous sodium sulphite powder (Na 2 SO 3 (s)); Calcium oxide powder (CaO(s)); Universal indicator solution; Tap water. 1. Repeat steps 1 to 3 in part Using the spooned end of a plastic microspatula, add three spatulas of anhydrous sodium sulphite powder into well E3. Insert lid 1 into well E3 in such a way that the tube connector is closest to the small wells and the syringe inlet is pointed away from the small wells. 3. Insert a small piece of cotton wool into the opening of one end of the silicone tube. Thereafter fit this end of the tube over the tube connector on lid Use the narrow end of a clean, plastic microspatula to add calcium oxide powder into the other end of the silicone tube. Add sufficient calcium oxide powder to fill the silicone tube up. Try to pack the calcium oxide quite tightly into the tube so that it is not forced out of the tube when the hydrochloric acid is added into the well. This will be the emission absorber. silicone tube tube connector As in part 1, the remaining steps may be performed in a draught-free area. CaO powder packed cotton wool 5. Fill the syringe with 0,2 ml of hydrochloric acid. Fit the syringe into the syringe inlet in lid 1. Add all of the 5.5 M hydrochloric acid into well E3. Do not add the acid too quickly as the increase in pressure in the well may force all the calcium oxide out of the silicone tube. Be careful not to drop any of the hydrochloric acid into the water. 6. Immediately after completing step 5, remove the syringe from the inlet in lid 1 and seal the inlet with a piece of plasticine. pollution source (SO 2 (g) emitted from well E3) water source cotton wool chimney filled with CaO emission absorber plasticine ball to seal syringe inlet on lid 1 lid 1 7. Wait about three to five minutes and observe. (See Question 1) Clean the comboplate thoroughly. QUESTIONS Q1. In how many wells has the water been acidified? (Answer this no longer than 5 minutes from the time you began the experiment.) Q2. Write down a balanced chemical equation to show the reaction between the SO 2 (g) and the CaO(s) in the chimney. Q3. What is the answer to focus question 2? 12

13 SOURCES OF SUBSTANCES IN WATER SOLUBILITY OF GASES IN WATER There are four gases that will be tested for solubility. These are sulphur dioxide, carbon dioxide, oxygen and nitrogen. Below is a procedure given for preparing each gas. The class can be divided so that each group can prepare one gas and observe the solubility collectively. For best results prepare the gases and start the solubility test on Friday with the results to be observed on Monday. Part 1: PREPARATION OF SULPHUR DIOXIDE Apparatus: Chemicals: 1 x comboplate ; 1 x lid 1; 1 x lid 2; 1 x silicone tube (4 cm x 4 mm); 1 x 2 ml syringe; 1 x plastic microspatula; 1 x piece prestik; 1 x dish for water; 1 x small sample vial marked sulphur dioxide. Hydrochloric acid (HCl(aq)) [5.5 M]; Anhydrous Sodium sulphite powder (Na 2 SO 3 (s)); Tap water; Fridge water that has been previously boiled. 1. Fill ¾ of the dish with the fridge water. Place it to one side. 2. Insert the small sample vial into well F4. 3. Using the spooned end of the microspatula, put 4 spatulas of solid Na 2 SO 3 (s) into well F2. 4. Seal well F2 with lid 2. Seal the sample vial in well F4 with lid Connect one end of the silicone tube to the tube connector on lid 2. Connect the remaining end of the silicone tube to the tube connector on lid Fill the syringe with 1 ml of 5.5 M HCl(aq) and insert the nozzle of the syringe into the inlet on lid Inject 1-2 drops of 5.5 M HCl(aq) into well F2. After a while block the opening on lid 1 on the sample vial with a piece of prestik. Now inject the rest of the 5.5 M HCl(aq) slowly. Wait 1-2 mins after all the 5.5 M HCl(aq) has been added to well F2. 8. Now remove lid 1 from the sample vial with one hand and block the opening of the sample vial with the thumb of your other hand. Quickly invert the sample vial in the water of the dish. Place to one side. inverted sample vial containing sulphur dioxide dish fridge water 13

14 SOLUBILITY OF GASES IN WATER Part 2: PREPARATION OF CARBON DIOXIDE Apparatus: Chemicals: 1 x comboplate ; 1 x lid 1; 1 x lid 2; 1 x silicone tube (4 cm x 4 mm); 1 x 2 ml syringe; 1 x plastic microspatula; 1 x piece prestik; 1 x dish for water; 1 x small sample vial marked carbon dioxide. Hydrochloric acid (HCl(aq)) [5.5 M]; Calcium carbonate powder (CaCO 3 (s)); Tap water; Fridge water that has been previously boiled. 1. Fill ¾ of the dish with fridge water. Place it to one side. 2. Insert the small sample vial into well F4. 3. Using the spooned end of the microspatula, put 4 spatulas of solid CaCO 3 (s) into well F2. 4. Seal well F2 with lid 2. Seal the sample vial in well F4 with lid Connect one end of the silicone tube to the tube connector on lid 2. Connect the remaining end of the silicone tube to the tube connector on lid Fill the syringe with 1 ml of 0.1 M HCl(aq) and insert the nozzle of the syringe into the inlet on lid Inject 1-2 drops of 0.1 M HCl(aq) into well F2. After a while block the opening on lid 1 on the sample vial with a piece of prestik. Now inject the rest of the 0.1 M HCl(aq) very slowly. Wait 1-2 mins after all the 0.1 M HCl(aq) has been added to well F2. 8. Now remove lid 1 from the sample vial with one hand and block the opening of the sample vial with the thumb of your other hand. Quickly invert the sample vial in the water of the dish. Place to one side. Part 3: PREPARATION OF OXYGEN Apparatus: 1 x comboplate ; 1 x lid 1; 1 x lid 2; 1 x silicone tube (4 cm x 4 mm); 1 x 2 ml syringe; 1 x plastic microspatula; 1 x piece prestik; 1 x dish for water; 1 x small sample vial marked oxygen. Chemicals: Manganese dioxide powder (MnO 2 (s)); Fresh hydrogen peroxide solution (H 2 O 2 (aq))[10 %]; Tap water; Fridge water that has been previously boiled. 1. Fill ¾ of the dish with fridge water. Place it to one side. 2. Insert the small sample vial into well F4. 3. Using the spooned end of the microspatula, put 4 spatulas of solid MnO 2 (s) into well F2. 4. Seal well F2 with lid 2. Seal the sample vial in well F4 with lid Connect one end of the silicone tube to the tube connector on lid 2. Connect the remaining end of the silicone tube to the tube connector on lid Fill the syringe with 1 ml of 10% H 2 O 2 (aq) and insert the nozzle of the syringe into the inlet on lid Inject 1-2 drops of 10% H 2 O 2 (aq) into well F2. After a while block the opening on lid 1 on the sample vial with a piece of prestik. Now inject the rest of the 10% H 2 O 2 (aq) slowly. Wait 1-2 mins after all the 10% H 2 O 2 (aq) has been added to well F2. 8. Now remove lid 1 from the sample vial with one hand and block the opening of the sample vial with the thumb of your other hand. Quickly invert the sample vial in the water of the dish. Place to one side. 14

15 SOLUBILITY OF GASES IN WATER Part 4: PREPARATION OF NITROGEN Apparatus: Chemicals: 1 x dish for water; 1 x small sample vial marked nitrogen. Fridge water that has been previously boiled. 1. Fill ¾ of the dish with fridge water. 2. Since the air is made up of 78 % nitrogen, the air in the sample vial will be used as a sample of nitrogen gas. Invert the sample vial in the water of the dish. Place to one side. QUESTIONS 1. Why does the water rise in some of the tubes and not in others? 2. Compare the extent to which the water has risen in each vial. 3. What does this tell you about the solubility of each of the gases? 15

16 CHAPTER 2 WATER TESTING 16

17 WATER TESTING THE TEST FOR DISSOLVED OXYGEN PART 1: HOW CAN WE TEST FOR DISSOLVED OXYGEN IN WATER? PART 2: WHAT IS THE EFFECT OF TEMPERATURE ON THE CONCENTRATION OF DISSOLVED OXYGEN IN WATER? TESTING FOR THE ACIDITY/BASICITY OF DRINKING WATER THE TEST FOR NITRATE IN WATER TESTING FOR PHOSPHATE IN DRINKING WATER PART 1 DOES THE WATER SOURCE THAT YOU DRINK FROM HAVE AN ACCEPTABLE PHOSPHATE CONTENT? (SILVER NITRATE TEST) PART 2 DOES THE WATER SOURCE THAT YOU DRINK FROM HAVE AN ACCEPTABLE PHOSPHATE CONTENT? (AMMONIUM MOLYBDATE TEST) TESTING FOR THE PRESENCE OF HEAVY METAL IONS IN WATER TESTING THE CONDUCTIVITY OF WATER TESTING FOR HARDNESS IN WATER

18 WATER TESTING THE TEST FOR DISSOLVED OXYGEN Part 1: How can we test for dissolved oxygen (O 2 (aq)) in water? Apparatus: Chemicals: 1 x comboplate ; 1 x glass sample vial; 1 x stopper to fit glass vial; 1 x 2 ml syringe; 3 x thin stemmed propettes; 1 x plastic microspatula; 1 x thermometer. Manganese(II) sulphate solution (MnSO 4 (aq)); Sodium hydroxide-potassium iodide solution (NaOH/KI(aq)); Hydrochloric acid (HCl(aq)) [11M]; Soluble starch powder; Tap water. INTRODUCTION Dissolved oxygen in the water is very important for organisms that live in the water, such as fish, frogs, and water insects. If the level of dissolved oxygen (DO) changes, the water ecosystems can be affected, eg. a decrease in the DO concentration can cause the death of one or more life stages of certain water insects. Record the location of the test site and the temperature of the water below: Place where water was collected: Temperature of water: 1. Immerse the sample vial into the water, which you are going to test. Allow the vial to fill until it is overflowing. If you are collecting water from a tap, gently fill the sample vial with the water from the tap until the vial is overflowing. Make sure that there are no air bubbles trapped in the sample vial. Do not place the stopper into the vial. 2. Carefully place the sample vial on a surface upon which you can work without upsetting the water sample. Insert the 2 ml syringe into the solution of manganese(ii) sulphate (MnSO 4 (aq)) and remove 0,5 ml of the solution. There must not be any air bubbles in the syringe! 3. Place the tip of the syringe containing the MnSO 4 (aq) about halfway into the sample vial. Carefully push in the plunger of the syringe and add all of the MnSO 4 (aq) to the water sample. Some of the sample will flow out of the vial. Do not be concerned about this. 4. Rinse the syringe with clean tap water and dry it. Insert the cleaned syringe into the sodium hydroxidepotassium iodide solution (NaOH/KI(aq)) and remove 0,5 ml of this solution. Make sure that you do not have any air bubbles in the syringe. 5. Insert the syringe about halfway into the sample vial as before and carefully add all of the NaOH/KI(aq) to the water sample. (See Question 1) 6. Once you have completed step 5, push the stopper into the sample vial. This must be done in such a way that some of the water is pushed out of the vial. This will prevent any air bubbles from entering the sample vial. 7. When the stopper is firmly in place, invert the sample vial (turn it upside down) a few times to mix the contents of the vial. 8. Allow the precipitate to settle about halfway down the sample vial and then invert the vial again to remix the contents. Allow the precipitate to settle as before. 9. Rinse the 2 ml syringe with clean tap water and dry it. Fill the syringe with 1 ml of 11 M hydrochloric acid (HCl(aq)), making sure that no air bubbles are present in the syringe. Be very careful with the hydrochloric acid. If any acid drops onto the skin, rinse immediately with water. 18

19 10. Carefully remove the stopper from the sample vial so that no air enters the water sample. Insert the tip of the 2 ml syringe about halfway into the sample vial and add all of the 11 M HCl(aq) to the sample. (See Question 2) 11. Replace the stopper in the sample vial in the same way as you did before. Carefully invert the sample vial a few times to mix the contents of the sample vial. (See Question 3) 12. Continue to mix the contents of the vial until all of the precipitate is dissolved. There should be no visible solid particles floating in the sample. The oxygen in the sample is now "fixed". The sample can be exposed to air at this stage. (If the sample has not been collected in the classroom, it can now be transported back there.) 13. Rinse the 2 ml syringe again with tap water and dry it. Insert the syringe into the sample vial and remove 2 ml of the sample from the vial. 14. Dispense the 2 ml sample from the syringe into well F1 of the comboplate. 15. Pick up the plastic microspatula. Insert the narrow end of the microspatula into the soluble starch powder and remove a little powder. The powder must not be heaped on the microspatula. Tap the microspatula gently to remove excess powder. small quantity of starch powder at end of microspatula 16. Add the starch powder to the water sample in well F1. Stir the contents of well F1 to mix in the starch indicator. (See Question 4) 17. Put the comboplate to one side. Do not throw away the sample in well F1 because you need it for Part 2. QUESTIONS Q1. What do you notice in the sample vial after adding both the MnSO 4 (aq) and the NaOH/KI(aq) to the water? Q2. What happens inside the sample vial when the HCl(aq) is added? Q3. What happens while the contents of the vial are being mixed? Q4. What happens in well F1 when the starch indicator is added? Q5. What is the answer to the focus question? Q6. Do you think more or less oxygen dissolves in warm water than in cold water? 19

20 THE TEST FOR DISSOLVED OXYGEN Part 2: What is the effect of temperature on the concentration of dissolved oxygen in water? The temperature of the water can affect how much oxygen from the atmosphere will dissolve in the water. To determine the concentration of oxygen dissolved in the water, one can observe how dark the blue black colour of the starch indicator becomes when it is added to the water sample. If the concentration of dissolved oxygen is small, the indicator is more purple in colour and if there is a larger concentration of dissolved oxygen, the starch indicator will be more black in colour. Apparatus: Chemicals: 1 x comboplate ; 1 x glass sample vial; 1 x stopper to fit glass vial; 1 x 2 ml syringe; 3 x thin stemmed propettes; 1 x plastic microspatula. Manganese(II) sulphate solution (MnSO 4 (aq)); Sodium hydroxide-potassium iodide solution (NaOH/KI(aq)); Hydrochloric acid (HCl(aq)) [11M]; Soluble starch powder; Tap water; Boiled water cooled to 30 0 C C. 1. Collect the water sample provided (30-40 C) in the same way as instructed in step 1 of Part 1. Repeat steps 2 to 7 in Part 1 using the warm water sample. (See Question 1) 2. Repeat steps 8 to 12 in Part 1 with the warm water sample. 3. Once the oxygen has been "fixed", remove the stopper from the sample vial. Clean the 2 ml syringe and use it to withdraw 2 ml of the sample from the vial. 4. Transfer the sample from the syringe into well F2 of the comboplate. 5. The sample should already be pale yellow in colour. Use the narrow end of a clean microspatula to add the same quantity of starch indicator powder to the sample in well F2 as you did to well F1 (see step 15 in Part 1). Stir the contents of well F2 with the microspatula. QUESTIONS Q1. What is the difference between the precipitate formed with the water sample in Part 1 and that formed with the warm water sample here, after the addition of the MnSO 4 (aq) and the NaOH/KI(aq)? Q2. Compare the colour of the solution you obtained with the warm water in well F2 with that from Part 1 in well F1, after the starch has settled at the bottom of the well. What is the difference between the two solutions? Q3. Examine the colour of the solid indicator at the bottom of each well by looking directly down into wells F1 and F2. What is the difference between the two solids? Q4. Is the concentration of oxygen dissolved in the water sample lower or higher at the higher temperature? Give a reason for your answer. Q5. What is the answer to the focus question? 20

21 WATER TESTING TESTING FOR THE ACIDITY/BASICITY OF DRINKING WATER Focus Question: What is the acidity/basicity of the water source that you drink from? Apparatus: Chemicals: 1 x comboplate ; 5 x thin stemmed propettes; 1 x plastic microspatula; 1 x filter funnel; 1 x filter paper. Sodium hydroxide solution (NaOH(aq)) [0.10 M]; Hydrochloric acid (HCl(aq)) [0.10 M]; Universal indicator solution; Tap water. 1. Dispense 10 drops of HCl (0.10 M) into well A1. 2. Dispense 10 drops of tap water into well A2. 3. Dispense 10 drops of NaOH (0.10 M) into well A3. 4. Add 1 drop of universal indicator solution into each well. Note the colour of the solution in each well and write this down in Table 2. (See Question 1) ** Stir the solution in each well with a cleaned plastic microspatula if you are uncertain of the colour change. 5. Dispense 10 drops of sample water into well A4. (This sample can be obtained from a river, a pond, or any other source that you'd like to test. However, make sure to filter off any solid particles (mud, sticks, grass etc.) that may interfere with this test. Use the filter funnel and filter paper for this purpose.) 6. Add 1 drop of universal indicator solution into well A4. Note the colour of this solution and write this down in Table 2. (See Question 2) ** Stir the solution in well A4 with a cleaned plastic microspatula if you are uncertain of the colour change. Rinse the wells with tap water, and then shake them dry. 21

22 TESTING FOR THE ACIDITY/BASICITY OF DRINKING WATER Q1. Construct a table like Table 2 in your books. QUESTIONS Use Table 1 to describe the acidity/basicity of the solutions in wells A1, A2 and A3 i.e. whether the solutions are very acidic, slightly acidic, neutral, slightly basic or very basic. Record your observations in the space provided in Table 2. TABLE 1 Colour of Universal Indicator Solution in Sample Tested Dark Red to Light Red Dark Orange to Yellow Light Green Dark Green to Dark Blue Light Purple to Dark Purple Description Very acidic Slightly acidic Neutral Slightly basic Very basic TABLE 2 Well Number Colour of Universal Indicator Solution Description A1 A2 A3 A4 (water sample) Q2. Use Table 1 to describe the acidity/basicity of the water sample in well A4. Record your observation in Table 2 as before. The acidity/basicity of each sample tested may be different. Thus the answers obtained for well A4 may vary. Q3. What is the answer to the focus question? 22

23 WATER TESTING THE TEST FOR NITRATE IN WATER Focus Question: Does the water source that you test have an acceptable * nitrate (NO 3 - (aq)) concentration for drinking? Apparatus: 1 x comboplate ; 1 x 2 ml syringe; 1 x thin stemmed propette; 1 x plastic microspatula; 1 x lid 1; 1 x lid 2; 1 x silicone tube; 1 x filter funnel; 1 x filter paper. Chemicals: Sodium hydroxide solution (NaOH(aq)) [5.0 M]; Devarda's alloy (5%Zn: 50%Cu: 45%Al); Magnesium nitrate solution (Mg(NO 3 ) 2 (aq)) [0.001 M]; Universal indicator solution. syringe inlet tube connectors vent syringe LID 1 LID 2 silicone tube 0.2 ml 5.0 M NaOH(aq) tap water 0.5 ml M Mg(NO 3 ) 2 (aq) 2 spatulas Devarda s Alloy 1. Fill ¾ of well F1 with water from the tap. Add one drop of universal indicator solution into the water, with a propette. Note the colour of the universal indicator. (See Question 1) 2. Using the spooned end of the microspatula, put 2 microspatulas of Devarda's alloy into well F2. 3. Use the syringe to add 0.5 ml of magnesium nitrate solution into well F2. Thoroughly clean the syringe with water before proceeding with the next step. 4. Seal well F1 with lid 2. Make sure the vent hole faces inwards (see figure above). Seal well F2 with lid Connect one end of the silicone tube to the silicone tube connector on lid 1. Connect the remaining end of the silicone tube to the silicone tube connector on lid Refill the cleaned syringe with 0.2 ml of sodium hydroxide solution (5.0 M) and connect the nozzle of the syringe into the syringe inlet on lid 1 (see the figure above for the complete set-up). 7. Inject the 0.2 ml of sodium hydroxide solution (5.0 M) very slowly into well F2. Shake the comboplate gently back and forth a couple of times to thoroughly mix the contents in well F2. Make sure the appropriate lids are placed in wells F1 and F2 or the base may be forced up through the silicone tube, making it necessary to restart the experiment. 8. Wait about 1 minute, from the time you added the sodium hydroxide, and observe what happens. (See Questions 2-5) 9. After about 5 minutes, remove the lid from well F1 and smell the contents as before to confirm your previous observation. Note the colour of the universal indicator solution. (See Question 6) 23

24 10. Clean the comboplate thoroughly, then repeat steps 1 to 9. This time use a water sample of unknown composition in step 3. (This sample may be obtained from a river, a pond, or any other water source that you'd like to test. However, make sure to filter off any solid particles (mud, sticks, grass etc.) that may prevent you from detecting a ph change. Do this first with the filter funnel and filter paper supplied.) 11. Answer Question 7. QUESTIONS Q1. Is the water acidic, basic or neutral? Q2. What do you observe happening in well F2? Q3. Can you smell anything from the vent in well F1? (Wave your hand across the vent bringing your nose close to the vent, but not directly over it.) If you can smell something, describe what you smell. Q4. What gas do you think this is? Q5. Write down a chemical formula for the gas formed in well F2. Q6. What is the colour of the indicator? Is the solution in the well acidic, basic or neutral? What do you deduce from this observation? Q7. What is the answer to the focus question? 24

25 WATER TESTING TESTING FOR PHOSPHATE IN DRINKING WATER Part 1 3- Focus Question: Does the water source that you drink from have an acceptable phosphate (PO 4 (aq)) content? Apparatus: Chemicals: 1 x comboplate ; 1 x 2 ml syringe; 3 x thin stemmed propettes; 1x plastic microspatula; 1 x filter funnel; 1 x filter paper. Disodium hydrogenphosphate solution (Na 2 HPO 4 (aq)) [0.001 M]; Silver nitrate (AgNO 3 (aq)) [0.10 M]; Dilute nitric acid (HNO 3 (aq)) [2.0 M] 1. Use a propette to half fill well F1 with the solution of disodium hydrogenphosphate (0.001 M). 2. Add 10 drops of silver nitrate solution (0.10 M) into well F1. (See Question 1) 3. Add 10 drops of dilute nitric acid (2.0 M) to well F1. (See Question 2) 4. Repeat steps 1 to 3 in well F2, with a water sample of your choice. This sample may be obtained from a river, a pond, or any other water source that you'd like to test, from which you drink. However, make sure to filter off any solid particles (mud, sticks, grass etc.) that may prevent you from detecting a colour change. Do this first with the filter funnel and paper supplied. (See Question 3) Rinse the wells with tap water, and then shake them dry. QUESTIONS: Part 1 Q1. Note what happens as the silver nitrate is added to F1. Q2. Note what happens as the nitric acid is added to F1. Q3. Observe what happens when the test is repeated with your water sample in F2. If there is no colour change when testing your sample this could mean a number of things: 1. The concentration of phosphates present in the water is lower than this test can detect. 2. No phosphates are present. Q4. What is the answer to the focus question? 25

26 WATER TESTING TESTING FOR PHOSPHATE IN DRINKING WATER Part 2 3- Focus Question: Does the water source that you drink from have an acceptable phosphate (PO 4 (aq)) content? Apparatus: Chemicals: 1 x comboplate ; 1 x 2 ml syringe; 3 x thin stemmed propettes; 1x plastic microspatula; 1 x filter paper; 1 x filter funnel. Disodium hydrogenphosphate solution (Na 2 HPO 4 (aq)) [0.001 M]; Dilute nitric acid (HNO 3 (aq)) [2.0 M]; Ammonium molybdate reagent ((NH 4 ) 2 MoO 4 (aq)). 1. Use the 2 ml syringe to dispense 0,5 ml of the disodium hydrogenphosphate solution (0.001 M) into well F1. 2. Rinse the syringe with tap water. Use the cleaned syringe to add 0,3 ml of the nitric acid to the Na 2 HPO 4 (aq) in well F1. 3. Rinse the syringe again and use it to add 1,5 ml of the ammonium molybdate reagent to the solution in well F1. (See Question 1) 4. Repeat steps 1 to 3 in well F2, with a water sample of your choice. This sample may be obtained from a river, a pond, or any other water source that you'd like to test, from which you drink. However, make sure to filter off any solid particles (mud, sticks, grass etc.) that may prevent you from detecting a colour change. Do this first with the filter funnel and paper supplied. (See Questions 2, 3) Rinse the wells with tap water, and then shake them dry. QUESTIONS: Part 2 Q1. Note what happens as the ammonium molybdate reagent is added to F1. Q2. Observe what happens when the test is repeated with your water sample in F2. If there is no colour change when testing your sample this could mean: 1. The concentration of phosphates present in the water is lower than this test can detect. 2. No phosphates are present. Q3. What is the answer to the focus question? 26

27 WATER TESTING TESTING FOR THE PRESENCE OF HEAVY METAL IONS IN WATER Focus Question: Does the water source that you test have any heavy metal ions (e.g. Cu 2+ (aq), Zn 2+ (aq), Pb 2+ (aq)) present? Apparatus: 1 x comboplate ; 1 x 2 ml syringe; 5 x thin stemmed propette; 3 x plastic microspatula; 1 x lid 1; 1 x lid 2; 1 x silicone tube; 1 x filter funnel; 1 x filter paper. Chemicals: Hydrochloric acid (HCl(aq)) [5.5 M]; Iron sulphide powder (FeS(s)); Copper nitrate solution (Cu(N0 3 ) 2 (aq)) [0.1 M]; Zinc nitrate solution (Zn(N0 3 ) 2 (aq)) [0.1 M]; Lead nitrate solution (Pb(N0 3 ) 2 (aq)) [0.1 M]; Tap water; Water sample. If any acid is spilt on the skin thoroughly rinse the affected area with water. syringe syringe inlet tube connectors LID 1 LID 2 vent silicone tube 0.5 ml 5.5 M HCl (aq) tap water 1 level spatula of FeS(s) F1 F2 1. Fill ¾ of well F1 with water from the tap. 2. Put 1 level microspatula of solid iron sulphide (FeS(s)) into well F2, using the spooned end of the microspatula. 3. Seal well F1 with lid 2. Make sure the vent hole faces inwards (see figure). Seal well F2 with lid Connect one end of the silicone tube to the silicone tube connector on lid 1. Connect the remaining end of the silicone tube to the silicone tube connector on lid Fill the syringe with 0.5 ml of 5.5 M HCl and connect the nozzle of the syringe into the syringe inlet on lid 1 (see figure above for complete set-up). 6. Inject the 0.5 ml of 5.5 M HCl very slowly into well F2. Make sure the appropriate lids are placed in wells F1 and F2 or the acid may be forced up through the silicone tube, making it necessary to restart the experiment. 7. Wait about 3 minutes, from the time you added the hydrochloric acid. Answer Questions 1-3 while you wait. 27

28 8. After 3 minutes has elapsed, use the empty propette provided to suck up most of the aqueous hydrogen sulphide solution in well F1. 9. Add 8 drops of aqueous hydrogen sulphide (H 2 S(aq)) solution into wells A1, A2 and A Add 5 drops of the copper nitrate solution (0.1 M) into well A1. Stir the solution with a clean microspatula. (See Question 4) 11. Add 5 drops of lead nitrate solution (0.1 M) into well A2. Stir the solution with a different microspatula. (See Question 5) 12. Add 5 drops of zinc nitrate solution (0.1 M) into well A3. Stir the solution with a different microspatula. (See Question 6) 13. Add 8 drops of sample water of unknown composition in wells B1, B2, B3. This sample may be obtained from a river, a pond, or any other water source that you'd like to test. However, make sure to filter off any solid particles (mud, sticks, grass etc.) that may prevent you from detecting a colour change. Use the filter funnel and filter paper provided to do this. 14. Add 5 drops of the remaining aqueous hydrogen sulphide solution into each well. (See Question 7) QUESTIONS Q1. What do you observe happening in well F1? Q2. Can you smell anything from the vent in well F1? If so, what do you think this smell is due to? Q3. Write down a chemical formula for the gas formed in well F2. Gaseous hydrogen sulphide is a weak acid. When it dissolves in water the following reaction occurs: H 2 S(g) + H 2 O(l) HS - (aq) + H 3 O + (aq) Thus well F1 contains an aqueous solution of hydrogen sulphide. Q4. Note the appearance of the mixture in well A1. Explain what you observe. Q5. Note the appearance of the mixture in well A2. Explain what you observe. Q6. Note the appearance of the mixture in well A3. Explain what you observe. We see from these observations that aqueous hydrogen sulphide reacts with heavy metal ions in solution to form insoluble metal sulphides. Q7. What is the answer to the focus question? 28

29 WATER TESTING TESTING THE CONDUCTIVITY OF WATER Focus Question: What can testing the conductivity of a water sample, tell us about that sample? Apparatus: Chemicals: 1 x comboplate ; 1 x 2 ml syringe; 1 x thin stemmed propette; 1x plastic microspatula; 1 x LED current indicator with connections; 1 x filter funnel; 1 x filter paper; 1 x 9V battery. (or Bar LED Conductivity Meter) Hydrochloric acid (HCl(aq)) [0.1 M]; Tap water; Water sample. INTRODUCTION In this experiment hydrochloric acid will be diluted in a series dilution. The aim of this experiment is to determine what effect diluting this solution will have on the conductivity, and then to compare this conductivity with a sample of water of unknown composition. 1. Use the syringe to add 0.1 ml of hydrochloric acid (0.10 M) into well E1. 2. Rinse the syringe with tap water to clean it. Add 1.9 ml of tap water into well E1. 3. Stir the solution in well E1 with the spooned end of the microspatula to mix the contents. 4. Make sure that the syringe is dry inside, then suck up 0.1 ml of the solution in well E1 with the syringe. Place this into well E2. Rinse the syringe with tap water to clean it. Dispense 1.9 ml of tap water into well E2. 5. Stir the solution in well E2 with the spooned end of the cleaned microspatula to mix the contents. 6. Make sure that the syringe is dry inside, then suck up 0.1 ml of the solution in well E2 with the syringe. Place this into well E3. Rinse the syringe with tap water to clean it. Dispense 1.9 ml of tap water into well E3. 7. Stir the solution in well E3 with the spooned end of the cleaned microspatula to mix the contents. 8. Make sure that the syringe is dry inside, then suck up 0.1 ml of the solution in well E3 with the syringe. Place this into well E4. Rinse the syringe with tap water to clean it. Dispense 1.9 ml of tap water into well E4. 9. Stir the solution in well E4 with the spooned end of the cleaned microspatula to mix the contents. 10. Push the lid with the current indicator into well E Connect the current indicator to the terminals of the 9 V battery, as shown in the diagram. 12. Connect each of the crocodile clips to a carbon rod (pencil lead) as shown in the diagram. 13. Insert the carbon rod connected to the long black wire into the solution in well E1. Insert the carbon rod connected to the long end of the red wire into the same solution in well E1. Take care that the carbon rods do not touch in the solution. black wire connected to positive terminal of the battery crocodile clips connecting wires of the LED to the carbon rods red wire connected to negative terminal of the battery carbon rods immersed in the HCl(aq) in well E1 E1 light emitting diode (LED) in E6 E6 + 9V _ BATTERY 14. Observe what happens to the red light emitting diode (LED) in the current indicator. (See Questions 1, 2) 15. Wipe the carbon rods clean and then test the conductivity of the solutions in wells E2, E3 and E4 in the same way. (See Question 3) 16. Use the clean syringe to add 2.0 ml of sample water into well E5. This water sample may be obtained from a river, a pond, or any other water source that you'd like to test. However, make sure to filter off any solid particles (mud, sticks, grass etc.) that may interfere with this test. Test the conductivity of the sample as before. (See Questions 4, 5) 29

30 TESTING THE CONDUCTIVITY OF WATER Q1. Prepare a table like Table 1 below. Table 1. Experimental observations QUESTIONS Well Concentration HCl(aq)/M LED glow: very dull, dull, bright, very bright? E E E E E5 (sample water) Q2. Enter your observations from step 14. Q3. Enter your observations from step 15. Q4. Record your results for your water sample in the table. (Note: Your answers may vary according to the water source that you tested.) Q5. What is the answer to the focus question? 30

31 WATER TESTING TESTING FOR HARDNESS IN WATER Focus Question: How can soap be used to test for hardness in water? INTRODUCTION As water flows over rocks and soil, it dissolves a large number of chemicals present in the soil and making up the composition of the rock (eg. limestone, chalk etc.) If water contains large concentrations of dissolved calcium and/or magnesium ions (Ca 2+ (aq) and Mg 2+ (aq)), it is commonly called "hard water". Other ions, such as iron(iii) ions, can also contribute to the hardness of water. In natural waters, however, the concentrations of the Ca 2+ (aq) and Mg 2+ (aq) ions exceed that of any other metal ion. As a result, when we refer to the hardness of water, we mean the total concentration of calcium and magnesium dissolved in the water. This is expressed as mg/l of calcium carbonate (CaCO 3 ). The main household problem associated with hard water is that it interferes with the cleaning action of soaps and detergents. When soap is mixed with normal, "soft" water (i.e. water containing low concentrations of Ca 2+ (aq) and Mg 2+ (aq)), it dissolves and forms a solution with a foam, or sudsy layer, on top. In contrast, a mixture of soap and hard water forms very little or no foam. The hard water cleans poorly, depositing a scum on clothes, skin and hair. If the water contains very high concentrations of calcium and magnesium ions, solid deposits of scale form inside water pipes. These deposits can become so thick that nearly all of the water flow through the pipe is cut off. Such deposits inside hot water heaters produce rock-like scales that act as thermal insulators. The heat flowing from the flame in a gas heater or from a heating element in an electric heater, is partially blocked. The heater can waste up to 25% of its energy because it requires more time to produce hot water. Extreme water hardness can also affect the metabolism of certain organisms. In our homes, we use a solution called a softener to remove the calcium and magnesium ions in the water used for washing clothes. Water supplied by wells is often very hard, and the calcium and magnesium ions are removed from the water with an ion exchange resin. The resin consists of polymer beads with sodium ions (Na + ) attached to them. When hard water flows through the resin, the calcium ions become attracted to the polymer beads while the sodium ions leave the resin and mix with the water. The ions are exchanged because the polymer beads have a greater attraction for the calcium ions than for the sodium ions. Apparatus: 1 x comboplate ; 1 x 2 ml syringe; 6 x thin stemmed propettes. Chemicals: Soap Solution [0.025%]; Calcium chloride solution (CaCl 2 (aq)) [0.1 M], [0.01 M], [0.001 M], [1 x 10-4 M]; * 'Soft' tap water. 1. Using the 2 ml syringe, dispense 0,5 ml of the 0.025% soap solution into each of wells F1, F2, F3, F4 and F5. 2. Rinse the syringe thoroughly with clean tap water. Use the clean syringe to add 0,5 ml of "soft" water to the soap solution in well F1. 3. Rinse the syringe again with tap water. Use the clean syringe to add 0,5 ml of the 1 x 10-4 M calcium chloride solution to the soap solution in well F5. Similarly, add 0,5 ml of the M calcium chloride solution to the soap solution in well F4. Add 0,5 ml of the 0.01 M calcium chloride to the soap solution in well F3. Add 0,5 ml of the 0.1 M CaCl 2 (aq) to the soap solution in well F2. If the calcium chloride solutions are added as set out in step 3, from least concentrated to most concentrated, then the syringe does not need to be rinsed between solutions. 4. Use a propette to suck up all of the solution (1 ml) in well F1. 5. Using 4 more clean propettes, repeat step 4 with the solutions in wells F2 to F5. 6. Shake each propette for about 30 seconds. Note what happens to the solution inside each propette while you are shaking it. 7. Stand the propettes in the comboplate for about 15 minutes by placing the bulb of each propette into one of the empty, large wells of the comboplate. 31

32 TESTING FOR HARDNESS IN WATER QUESTIONS Q 1. Q 2. Q 3. Q 4. Q 5. What do you notice after 15 minutes about the foam in the propette which contains the "soft" water and soap? What has happened to the foam in the propettes which contained the 0.1 M and the 0.01 M CaCl 2 (aq) solutions after 15 minutes? Have the foams of the M and 1 x 10-4 M CaCl 2 (aq) solutions changed in appearance after 15 minutes? Explain the changes, if any, in each foam. Use your answers to questions 1 to 3 to explain how hard water affects the ability of soap to form a foam. What is the answer to the focus question? 32

33 CHAPTER 3 WATER TREATMENT 33

34 WATER TREATMENT THE INDUSTRIAL PURIFICATION OF WATER: CHLORINATION WATER SOFTENERS: WATER SOFTENERS:

35 WATER TREATMENT THE INDUSTRIAL PURIFICATION OF WATER: CHLORINATION Focus Question: How can we chlorinate water? INTRODUCTION Before water can be used for human consumption, it must be purified at a water treatment plant. A combination of several procedures are used in the purification process. Some of these procedures include: Screening: A metal screen is used to prevent fish, sticks, weeds and other large objects from entering the treatment plant. Sand filtration: The screened water is passed through a number of sand filters to remove any suspended wastes. Chlorination: Chlorine has been used for decades to purify water. It has powerful disinfecting properties and kills bacteria, cysts, algae and viruses which are pathogenic (disease-causing). It also reacts with dissolved organic substances, such as phenols, to help decompose these. Sometimes, industrial wastes are chlorinated to destroy cyanides, to oxidise iron, or to reduce undesirable qualities in effluents such as colour and odour. Chlorine is added to the water at two steps in the water purification process. The pre-chlorination step involves adding chlorine to the sand filtered water. The post-chlorination step involves adjusting the chlorine concentration in the water just before it leaves the treatment plant, so that there is a small excess (residual) of chlorine in the water to destroy any bacteria that may enter the water supply after it leaves the plant. Chlorine may be added to water in three different ways. If a large quantity of water must be purified, chlorine gas (Cl 2 (g)) is used. It is stored in tanks at high pressure as a liquid. As the liquid is released from the tank, the pressure is reduced and it changes to chlorine gas, which is bubbled into the water at controlled concentrations. At smaller water treatment plants, a cheaper alternative is to introduce an aqueous solution of sodium hypochlorite (NaOCl(aq)) into the water. Dilute sodium hypochlorite solutions are available as laundry bleaches. The simplest method of chlorinating water is to add a solid substance, calcium- or sodium hypochlorite (Ca(OCl) 2 (s) or NaOCl(s)), to the water. It is available as pellets or a powder, and is commonly used to chlorinate swimming pool water. The purification of water is due to the hypochlorous acid molecule, HOCl. When either chlorine gas, aqueous sodium hypochlorite or solid calcium hypochlorite is dissolved in water, the hypochlorous acid molecule is formed. This molecule is responsible for killing the pathogenic organisms in the water. Apparatus: Chemicals: 1 x comboplate ; 1 x 2 ml syringe; 1x plastic microspatula; 1 x lid 1; 1 x lid 2; 1 x silicone tube; 2 x pieces blue litmus paper; 1 x felt-tip pen. Hydrochloric acid (HCl(aq)) [5.5 M]; Potassium permanganate powder (KMnO 4 (s)); Tap water. syringe syringe inlet tube connectors vent 1.0 ml 2.75 M HCl(aq) silicone tube LID 1 LID 2 1 microspatula KMnO 4 (s) tap water F1 F2 35

36 THE INDUSTRIAL PURIFICATION OF WATER: CHLORINATION 1. Using the spooned end of the microspatula, place 1 level spatula of solid potassium permanganate into well F1. 2. Place lid 1 on well F1. 3. Dilute the 5.5 M hydrochloric acid to 2.75 M hydrochloric acid by filling the syringe with 0.5 ml of tap water and dispensing it into well F6. Refill the syringe with 0.5 ml of 5.5 M HCl(aq) and add this dropwise to the water in well F6. You now have 2.75 M HCl(aq). Use this acid in step Fill the syringe with 1.0 ml of the 2.75 M HCl(aq) from well F6 and fit the syringe into the inlet in lid 1 covering well F1. 5. Fill ¾ of well F2 with tap water. Test the effect of the water on a piece of indicator paper. (See Question 1) 6. Cover well F2 with lid Join well F1 to well F2 by means of the silicone tubing. 8. Inject the solution of hydrochloric acid [2.75 M] dropwise into well F1 from the syringe. (See Questions 2-4) 9. After about 7 8 minutes, remove the lid from well F2. Using another piece of indicator paper, test the effect of the solution in well F2 on the paper. (See Question 5) 10. Write your initials on a strip of white paper using a koki pen. Place the paper into the solution in well F2. (See Question 6) AS SOON AS YOU HAVE COMPLETED THE TEST FOR THE EFFECT OF THE SOLUTION ON THE INK, RINSE THE COMBOPLATE THOROUGHLY OR THE BROWN SOLUTION WILL STAIN THE WELLS. IF THIS HAPPENS, ADD A FEW DROPS OF 10% H 2 O 2 (aq) TO THE STAINED WELLS AND SCRAPE THE WELLS CLEAN WITH A TOOTHPICK OR MATCHSTICK. Q 1. Q 2. Q 3. Q 4. Q 5. Q 6. Q 7. Q 8. Q 9. QUESTIONS Record the colour of the indicator paper with tap water. What happened in well F1 when you added hydrochloric acid to the potassium permanganate? What do you observe in the water in well F2 after HCl(aq) is added to the KMnO 4 (s)? Can you smell anything coming from the vent in the lid of well F2? (If you are unsure, wave your hand across the vent towards your nose.) Identify the smell. What is the colour of this second piece of indicator paper? What happens to the ink on the white paper? Explain the observations you made with the indicator paper and the ink writing on the white paper. Name the gas formed in well F1 and write its chemical formula. Write a chemical equation for the reaction occurring between the gas formed in well F1 and the water in well F2. Q10. What type of reaction occurred in well F1? (Hint: Think about the oxidation states of the different species in the reactants and the products.) Q11. Justify your answer to question 10. Q12. From your answers to questions 10 and 11, what kind of substances are required to obtain chlorine from hydrochloric acid? Q13. Examine the chemical equation you have written for question 9, as well as the following equation showing the reaction of aqueous sodium hypochlorite (bleach) with water. Identify and name the species in these equations that are responsible for the purification of water. Q14. What is the answer to the focus question? NaOCl(aq) + H 2 O(l) NaOH(aq) + HOCl(aq) EXTENSION QUESTIONS Q15. Which of the following substances would you use to produce chlorine (Cl 2 (g)) from hydrochloric acid (HCl(aq))? Explain your choice. 1. Sodium chloride (NaCl(s)) 2. Manganese dioxide (MnO 2 (s)) 3. Potassium chloride (KCl(s)) Q16. Write down a balanced chemical equation to show the reaction involved when solid calcium hypochlorite (Ca(OCl) 2 (s)) is added to swimming pool water. Use the equation to explain why it is used in pool water. 36

37 WATER TREATMENT WATER SOFTENERS: 1 Apparatus: Chemicals: 1 x propette; 1 x comboplate ; 1 x plastic retort stand ; 1 x plastic arm; 1 x microspatula; 2 x 2 ml syringes. Calcium chloride solution (CaCl 2.2H 2 O(aq)) [0.01 M]; Ammonium oxalate solution (COONH 4 ) 2.H 2 O(aq)) [1.0 M]; Amberlite (cross-linked polystyrene-divinyl benzene matrix) resin; Tap water. 1. Push the plastic retort stand into well D12 of the comboplate. Push the plastic arm onto the retort stand and orient the arms on the central stem of the retort stand so that one arm is directly above well F6. 2. Remove the plunger from the syringe. Using a microspatula add Amberlite to the syringe until it is threequarters full. Place the syringe in the arm that is directly above well F6. 3. Using a clean propette, add tap water to the syringe. If the syringe is not three-quarters full, add more Amberlite. Continue adding water until the water coming out at the bottom of the syringe into well F6, is clear. 4. Remove the plastic retort stand (with the syringe) from well D12 and push it into well D1. Orient the arm so that the arm with the syringe is directly above well F1. (See diagram below.) 5. Using a clean syringe, dispense 2 ml calcium chloride solution [0.01 M] into well F2. 6. Add 1 drop of ammonium oxalate solution to well F2. (See Question 1) 7. Using the syringe, slowly dispense 1,5 ml of calcium chloride solution [0.01 M] into the syringe containing the Amberlite. 8. Add 1 drop of ammonium oxalate solution to well F1. (See Question 2) retort stand syringe plastic arm QUESTIONS Q 1. What do you observe in well F2? Q 2. Describe what you observe in well F1. Q 3. Explain the difference in observation in wells F1 and F2. Q 4. Write a chemical equation for any chemical reactions you propose. 37

38 WATER TREATMENT WATER SOFTENERS: 2 Apparatus: Chemicals: 2 x propettes; 1 x comboplate ; 1 x glass rod; 1 x microspatula. Calcium chloride solution (CaCl 2.2H 2 O(aq)) [0.01 M]; Ammonium oxalate solution (COONH 4 ) 2.H 2 O(aq)) [1.0 M]; Pentasodiumtriphosphate (Na P O (s)) Using a clean propette, dispense calcium chloride solution [0.01 M] into well F1 and F2 until each is half full. 2. Add 1 drop of ammonium oxalate solution to both wells F1 and F2. (See Question 1) 3. To well F2, add half a microspatula of pentasodiumtriphosphate. Use the glass rod to stir the solution in well F2. (See Question 2) 4. Add a further half a microspatula of pentasodiumtriphosphate to well F2. Stir the solution again. (See Question 3) 5. Continue with step 4 until the solution in well F2 is clear. (See Question 4) pentasodiumtriphosphate calcium chloride solution + one drop ammonium oxalate solution QUESTIONS Q 1. What do you observe in both wells F1 and F2? Q 2. Describe what you observe in well F2. Q 3. Describe any further change in well F2. Q 4. Explain what you observe and write a chemical equation for any chemical reactions you propose. 38

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