WATER A guide for GCSE students

1. WATER A guide for GCSE students 2010 SPECIFICATIONS KNOCKHARDY PUBLISHING

2. WATER INTRODUCTION This Powerpoint show is one of several produced to help students understand selected GCSE Chemistry topics. It is based on the requirements of the AQA specification but is suitable for other examination boards. Individual students may use the material at home for revision purposes and it can also prove useful for classroom teaching with an interactive white board. Accompanying notes on this, and the full range of AS and A2 Chemistry topics, are available from the KNOCKHARDY WEBSITE at... www.knockhardy.org.uk All diagrams, photographs and any animations in this Powerpoint are original and created by Jonathan Hopton. Permission must be obtained for their use in any work that is distributed for financial gain.

3. WATER • CONTENTS • Properties of water • Occurrence of water – The water cycle • Hardness of water – the causes • Temporary hardness • Permanent hardness • Removing permanent hardness in water • Hard water – advantages and disadvantages • Water pollution and its treatment

4. PROPERTIES OF WATER GENERAL INFORMATION Structure Water consists of covalent molecules of formula H2O. Physical colourless, odourless liquid. properties boils at 100°C freezes at 0°C (if pure and at atmospheric pressure) Chemical Reacts with some metals to produce hydrogen. properties Uses Essential for life. An important solvent. A coolant for many industrial processes (e.g. power stations) Raw material in the manufacture of ammonia. Raw material in the conversion of ethene to ethanol. Test Turns blue cobalt chloride pink... or Turns white anhydrous copper(II) sulphate blue.

5. COMPOSITION OF WATER Fill both limbs of a Hofmann Voltameter with water which has been acidified with a small amount of dilute sulphuric acid. Pass sufficient direct current through the apparatus to enable measurable amounts of gas to be collected. ANODE (+) - a colourless gas collected - the gas re-lit a glowing splint CATHODE (-) - a colourless gas collected - its volume was twice that at anode - gas exploded with a squeaky pop when a lighted splint was applied Conclusion Water can be split into its elements by passing electricity through it. water ——> hydrogen (2 vols) + oxygen (1 vol) Dilute sulphuric acid is added to improve the conductivity of the water.

6. OCCURRENCE Water is the most abundant substance on the surface of our planet.

7. OCCURRENCE Water is the most abundant substance on the surface of our planet. ImportanceLIVING SYSTEMS RESOURCE FOR INDUSTRIAL PROCESSES

8. OCCURRENCE Water is the most abundant substance on the surface of our planet. Importance LIVING SYSTEMS RESOURCE FOR INDUSTRIAL PROCESSES OccurrenceOCEANS LAKES RIVERS ATMOSPHERE - clouds and water vapour

9. OCCURRENCE Water is the most abundant substance on the surface of our planet. Importance LIVING SYSTEMS RESOURCE FOR INDUSTRIAL PROCESSES Occurrence OCEANS LAKES RIVERS ATMOSPHERE - clouds and water vapour Water Cycle Shows the inter- relationship between water in different environments.

10. THE WATER CYCLE Shows the inter- relationship between water in different environments. Water evaporates from seas, lakes and rivers and from the leaves of plants. The water vapour produced condenses to form clouds and later falls as rain, hail and snow. The rain and snow complete the cycle by flowing down streams and rivers into lakes or seas. Some water seeps through rocks and soils to join underground reservoirs.

11. PURITY OF WATER Natural water is never pure. It is such a good solvent that it contains dissolved substances whatever its origin. RAIN dissolved gases from the air e.g. CO2, SO2 RIVERS dissolved salts from rocks and soils; also oxygen. SEA dissolved sodium and magnesium salts (e.g. NaCl) and CO2 water also contains man-made chemicals such as detergents, acids, fertilizers and other pollutants.

12. WHAT IS HARDNESS? “Hard water is water which does not readily form a lather with soap”

13. WHICH IONS CAUSE HARDNESS? “Hard water is water which does not readily form a lather with soap” Method Place a sample of one of the solutions in a test-tube to a depth of about 2cm. Using a dropping pipette, place a measured amount of soap solution into the water and shake vigorously for five seconds. Record the height of the lather. Repeat with another sample; decide which ions are responsible for hardness.

14. WHICH IONS CAUSE HARDNESS? “Hard water is water which does not readily form a lather with soap” Method Place a sample of one of the solutions in a test-tube to a depth of about 2cm. Using a dropping pipette, place a measured amount of soap solution into the water and shake vigorously for five seconds. Record the height of the lather. Repeat with another sample; decide which ions are responsible for hardness. A sodium sulphate B magnesium sulphate C potassium chloride D calcium chloride E sodium nitrate F magnesium nitrate G calcium nitrate H sodium chloride A B C D E F G H

15. WHICH IONS CAUSE HARDNESS? “Hard water is water which does not readily form a lather with soap” Method Place a sample of one of the solutions in a test-tube to a depth of about 2cm. Using a dropping pipette, place a measured amount of soap solution into the water and shake vigorously for five seconds. Record the height of the lather. Repeat with another sample; decide which ions are responsible for hardness. A sodium sulphate B magnesium sulphate C potassium chloride D calcium chloride E sodium nitrate F magnesium nitrate G calcium nitrate H sodium chloride A B C D E F G H

16. WHICH IONS CAUSE HARDNESS? “Hard water is water which does not readily form a lather with soap” Method Place a sample of one of the solutions in a test-tube to a depth of about 2cm. Using a dropping pipette, place a measured amount of soap solution into the water and shake vigorously for five seconds. Record the height of the lather. Repeat with another sample; decide which ions are responsible for hardness. Solution used ions present lather + ive - ive A sodium sulphate Na+ SO42- YES B magnesium sulphate Mg2+ SO42- NO C potassium chloride K+ Cl- YES D calcium chloride Ca2+ Cl- NO E sodium nitrate Na+ NO3- YES F magnesium nitrate Mg2+ NO3- NO G calcium nitrate Ca2+ NO3- NO H sodium chloride Na+ Cl- YES Conclusions The ion(s) responsible for hardness is / are...

17. WHICH IONS CAUSE HARDNESS? “Hard water is water which does not readily form a lather with soap” Method Place a sample of one of the solutions in a test-tube to a depth of about 2cm. Using a dropping pipette, place a measured amount of soap solution into the water and shake vigorously for five seconds. Record the height of the lather. Repeat with another sample; decide which ions are responsible for hardness. Solution used ions present lather + ive - ive A sodium sulphate Na+ SO42- YES B magnesium sulphate Mg2+ SO42- NO C potassium chloride K+ Cl- YES D calcium chloride Ca2+ Cl- NO E sodium nitrate Na+ NO3- YES F magnesium nitrate Mg2+ NO3- NO G calcium nitrate Ca2+ NO3- NO H sodium chloride Na+ Cl- YES Conclusions The ion(s) responsible for hardness is / are... Ca2+ and Mg2+

18. HARD WATER – HOW DOES IT ARISE? Definition “Water that does not readily form a lather with soap”. Instead, it forms an unsightly scum. Causes Arises from the solvation of compounds out of rocks / soils. The compounds are SOLUBLE magnesium or calcium salts.

19. HARD WATER – HOW DOES IT ARISE? Definition “Water that does not readily form a lather with soap”. Instead, it forms an unsightly scum. Causes Arises from the solvation of compounds out of rocks / soils. The compounds are SOLUBLE magnesium or calcium salts. ROCKS CONTAINING SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS LIMESTONE (CALCIUM CARBONATE) WATER

20. HARD WATER – HOW DOES IT ARISE? Definition “Water that does not readily form a lather with soap”. Instead, it forms an unsightly scum. Causes Arises from the solvation of compounds out of rocks / soils. The compounds are SOLUBLE magnesium or calcium salts. RAIN DISSOLVES THE SOLUBLE SALTS IN ROCKS ROCKS CONTAINING SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS LIMESTONE (CALCIUM CARBONATE) WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

21. HARD WATER – HOW DOES IT ARISE? Definition “Water that does not readily form a lather with soap”. Instead, it forms an unsightly scum. Causes Arises from the solvation of compounds out of rocks / soils. The compounds are SOLUBLE magnesium or calcium salts. LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO2 ROCKS CONTAINING SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS LIMESTONE (CALCIUM CARBONATE) WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

22. HARD WATER – HOW DOES IT ARISE? Definition “Water that does not readily form a lather with soap”. Instead, it forms an unsightly scum. Causes Arises from the solvation of compounds out of rocks / soils. The compounds are SOLUBLE magnesium or calcium salts. RAIN DISSOLVES THE SOLUBLE SALTS IN ROCKS LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO2 ROCKS CONTAINING SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS LIMESTONE (CALCIUM CARBONATE) WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

23. HARD WATER – HOW DOES IT ARISE? Definition “Water that does not readily form a lather with soap”. Instead, it forms an unsightly scum. Causes Arises from the solvation of compounds out of rocks / soils. The compounds are SOLUBLE magnesium or calcium salts. RAIN DISSOLVES THE SOLUBLE SALTS IN ROCKS LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO2 ROCKS CONTAINING SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS LIMESTONE (CALCIUM CARBONATE) WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

24. HARD WATER – HOW DOES IT ARISE? Definition “Water that does not readily form a lather with soap”. Instead, it forms an unsightly scum. Causes Arises from the solvation of compounds out of rocks / soils. The compounds are SOLUBLE magnesium or calcium salts. There are TWO main types of hardness…

25. HARD WATER – HOW DOES IT ARISE? Definition “Water that does not readily form a lather with soap”. Instead, it forms an unsightly scum. Causes Arises from the solvation of compounds out of rocks / soils. The compounds are SOLUBLE magnesium or calcium salts. There are TWO main types of hardness… PERMANENTHARDNESS TEMPORARY HARDNESS

26. TEMPORARY HARDNESS

27. TEMPORARY HARDNESS Source Atmospheric carbon dioxide dissolves in rain water making an acidic solution which reacts with limestone (calcium carbonate). Soluble calcium hydrogencarbonate is formed. CaCO3(s) + CO2(g) + H2O(l) ——> Ca(HCO3)2(aq) LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO2 ROCKS CONTAINING SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS LIMESTONE (CALCIUM CARBONATE) WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

28. TEMPORARY HARDNESS Source Atmospheric carbon dioxide dissolves in rain water making an acidic solution which reacts with limestone (calcium carbonate). Soluble calcium hydrogencarbonate is formed. CaCO3(s) + CO2(g) + H2O(l) ——> Ca(HCO3)2(aq) Removal Boiling the water reverses the above reaction. A white precipitate of insoluble calcium carbonate is produced. The calcium is thus removed from the water. Ca(HCO3)2(aq) ——> CaCO3(s) + CO2(g) + H2O(l)

29. TEMPORARY HARDNESS Source Atmospheric carbon dioxide dissolves in rain water making an acidic solution which reacts with limestone (calcium carbonate). Soluble calcium hydrogencarbonate is formed. CaCO3(s) + CO2(g) + H2O(l) ——> Ca(HCO3)2(aq) Removal Boiling the water reverses the above reaction. A white precipitate of insoluble calcium carbonate is produced. The calcium is thus removed from the water. Ca(HCO3)2(aq) ——> CaCO3(s) + CO2(g) + H2O(l) plus Any method used for removing permanent hardness. REMEMBER Only water containing SOLUBLE calcium and magnesium ions causes hardness.

30. TEMPORARY HARDNESS Source Atmospheric carbon dioxide dissolves in rain water making an acidic solution which reacts with limestone (calcium carbonate). Soluble calcium hydrogencarbonate is formed. CaCO3(s) + CO2(g) + H2O(l) ——> Ca(HCO3)2(aq) Removal Boiling the water reverses the above reaction. A white precipitate of insoluble calcium carbonate is produced. The calcium is thus removed from the water. Ca(HCO3)2(aq) ——> CaCO3(s) + CO2(g) + H2O(l) plus Any method used for removing permanent hardness. REMEMBER Only water containing SOLUBLE calcium and magnesium ions causes hardness.

31. PERMANENT HARDNESS

32. PERMANENT HARDNESS SourceSoluble calcium and magnesium compounds which dissolve in streams and rivers as they pass over and through rocks and soils. RAIN DISSOLVES THE SOLUBLE SALTS IN ROCKS ROCKS CONTAINING SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS LIMESTONE (CALCIUM CARBONATE) WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

33. PERMANENT HARDNESS SourceSoluble calcium and magnesium compounds which dissolve in streams and rivers as they pass over and through rocks and soils. SOLUBLE calcium chloride CaCl2 magnesium chloride MgCl2 magnesium sulphate MgSO4 INSOLUBLE calcium carbonate CaCO3 magnesium carbonate MgCO3

34. PERMANENT HARDNESS SourceSoluble calcium and magnesium compounds which dissolve in streams and rivers as they pass over and through rocks and soils. SOLUBLE calcium chloride CaCl2 magnesium chloride MgCl2 magnesium sulphate MgSO4 INSOLUBLE calcium carbonate CaCO3 magnesium carbonate MgCO3 REMEMBER Only water containing SOLUBLE calcium and magnesium ions causes hardness.

35. PERMANENT HARDNESS - REMOVAL DISTILLATION

36. PERMANENT HARDNESS - REMOVAL DISTILLATION Boil the water and collect pure water as the distillate. All the dissolved solids will be left behind. This is the only method to produce pure water. However, it is an expensive method because of the energy requirements. CONDENSER PURE WATER HARD WATER

37. PERMANENT HARDNESS - REMOVAL ION-EXCHANGE RESIN

38. PERMANENT HARDNESS - REMOVAL ION-EXCHANGE RESIN • Ion-exchange resins are special compounds containing Na+ or H+ ions • Hard water contains soluble calcium and/or magnesium ions RESIN

39. PERMANENT HARDNESS - REMOVAL ION-EXCHANGE RESIN • Ion-exchange resins are special compounds containing Na+ or H+ ions • Ca2+and Mg2+ ions in the hard water swap with those on the resin • The water comes out with Na+ ions in it • Ca2+and Mg2+ ions remain attached to the resin • Na+ and H+ ions do not cause hardness. Ca2+(aq) + 2Na+ ——> Ca2+ + 2Na+(aq) in hard water on resin on resin in softened water RESIN

40. PERMANENT HARDNESS - REMOVAL ION-EXCHANGE RESIN • Ion-exchange resins are special compounds containing Na+ or H+ ions • Eventually, all the Na+ ions get used up so the resin must be replaced or flushed through with sodium chloride solution to replace the calcium. RESIN

41. PERMANENT HARDNESS - REMOVAL SOAP

42. PERMANENT HARDNESS - REMOVAL SOAP Soap molecules have two distinctly different ends; HYDROPHOBIC HYDROPHILIC “water hating” “water liking” attracts oil and grease attracts water CHAIN OF CARBON ATOMS

43. PERMANENT HARDNESS - REMOVAL SOAP Soap molecules have two distinctly different ends; HYDROPHOBIC HYDROPHILIC “water hating” “water liking” attracts oil and grease attracts water When soap is placed in hard water, it reacts with the calcium and magnesium ions to produce an unsightly, insoluble grey scum. CHAIN OF CARBON ATOMS

44. PERMANENT HARDNESS - REMOVAL SOAP Soap molecules have two distinctly different ends; HYDROPHOBIC HYDROPHILIC “water hating” “water liking” attracts oil and grease attracts water When soap is placed in hard water, it reacts with the calcium and magnesium ions to produce an unsightly, insoluble grey scum. The scum is a calcium compound and is thus removed from the water. When all the hardness has been removed, the soap can act in the normal way. CHAIN OF CARBON ATOMS

45. PERMANENT HARDNESS - REMOVAL SOAP Soap molecules have two distinctly different ends; HYDROPHOBIC HYDROPHILIC “water hating” “water liking” attracts oil and grease attracts water CHAIN OF CARBON ATOMS In HARD WATER AREAS it is better to use SOAPLESS DETERGENTS which have structures similar to soap. Detergents form a lather without forming a scum. Because of this they DO NOT REMOVE HARDNESS.

46. PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate)

47. PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate) Sodium carbonate is one of the few soluble carbonates - it is a good source of soluble carbonate ions.

48. PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate) Sodium carbonate is one of the few soluble carbonates - it is a good source of soluble carbonate ions. Hard water contains soluble calcium (or magnesium) ions.

49. PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate) Sodium carbonate is one of the few soluble carbonates - it is a good source of soluble carbonate ions. Add the two solutions in order to mix the ions. Hard water contains soluble calcium (or magnesium) ions.

50. PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate) The Ca2+ and CO32- ions come together to form a precipitate of insoluble calcium carbonate. The calcium ions are removed from the water so it is now soft.