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WATER A guide for GCSE students 2010 SPECIFICATIONS KNOCKHARDY PUBLISHING.

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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... 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 CONTENTS 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 WATER

4 PROPERTIES OF WATER GENERAL INFORMATION StructureWater consists of covalent molecules of formula H 2 O. Physicalcolourless, odourless liquid. propertiesboils at 100°Cfreezes at 0°C (if pure and at atmospheric pressure) ChemicalReacts with some metals to produce hydrogen. properties UsesEssential 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. TestTurns 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 ConclusionWater 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 Importance LIVING 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 Occurrence OCEANS 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 CycleShows 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. RAINdissolved gases from the air e.g. CO 2, SO 2 RIVERSdissolved salts from rocks and soils; also oxygen. SEAdissolved sodium and magnesium salts (e.g. NaC l ) and CO 2 water also containsman-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 usedions presentlather + ive - ive A sodium sulphateNa + SO 4 2- YES B magnesium sulphateMg 2+ SO 4 2- NO C potassium chlorideK + C l - YES D calcium chlorideCa 2+ C l - NO E sodium nitrateNa + NO 3 - YES F magnesium nitrateMg 2+ NO 3 - NO G calcium nitrateCa 2+ NO 3 - NO H sodium chlorideNa + C l - YES ConclusionsThe 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 usedions presentlather + ive - ive A sodium sulphateNa + SO 4 2- YES B magnesium sulphateMg 2+ SO 4 2- NO C potassium chlorideK + C l - YES D calcium chlorideCa 2+ C l - NO E sodium nitrateNa + NO 3 - YES F magnesium nitrateMg 2+ NO 3 - NO G calcium nitrateCa 2+ NO 3 - NO H sodium chlorideNa + C l - YES ConclusionsThe ion(s) responsible for hardness is / are... Ca 2+ and Mg 2+

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

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

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

21 HARD WATER – HOW DOES IT ARISE? DefinitionWater that does not readily form a lather with soap. Instead, it forms an unsightly scum. CausesArises from the solvation of compounds out of rocks / soils. The compounds are SOLUBLE magnesium or calcium salts. LIMESTONE (CALCIUM CARBONATE) WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO 2 ROCKS CONTAINING SOLUBLE SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS

22 HARD WATER – HOW DOES IT ARISE? DefinitionWater that does not readily form a lather with soap. Instead, it forms an unsightly scum. CausesArises from the solvation of compounds out of rocks / soils. The compounds are SOLUBLE magnesium or calcium salts. LIMESTONE (CALCIUM CARBONATE) WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS RAIN DISSOLVES THE SOLUBLE SALTS IN ROCKS LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO 2 ROCKS CONTAINING SOLUBLE SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS

23 HARD WATER – HOW DOES IT ARISE? DefinitionWater that does not readily form a lather with soap. Instead, it forms an unsightly scum. CausesArises from the solvation of compounds out of rocks / soils. The compounds are SOLUBLE magnesium or calcium salts. LIMESTONE (CALCIUM CARBONATE) WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS RAIN DISSOLVES THE SOLUBLE SALTS IN ROCKS LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO 2 ROCKS CONTAINING SOLUBLE SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS

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

26

27 SourceAtmospheric carbon dioxide dissolves in rain water making an acidic solution which reacts with limestone (calcium carbonate). Soluble calcium hydrogencarbonate is formed. CaCO 3 (s) + CO 2 (g) + H 2 O(l) > Ca(HCO 3 ) 2 (aq) LIMESTONE (CALCIUM CARBONATE) WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO 2 ROCKS CONTAINING SOLUBLE SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS

28 TEMPORARY HARDNESS SourceAtmospheric carbon dioxide dissolves in rain water making an acidic solution which reacts with limestone (calcium carbonate). Soluble calcium hydrogencarbonate is formed. CaCO 3 (s) + CO 2 (g) + H 2 O(l) > Ca(HCO 3 ) 2 (aq) RemovalBoiling the water reverses the above reaction. A white precipitate of insoluble calcium carbonate is produced. The calcium is thus removed from the water. Ca(HCO 3 ) 2 (aq) > CaCO 3 (s) + CO 2 (g) + H 2 O(l)

29 TEMPORARY HARDNESS SourceAtmospheric carbon dioxide dissolves in rain water making an acidic solution which reacts with limestone (calcium carbonate). Soluble calcium hydrogencarbonate is formed. CaCO 3 (s) + CO 2 (g) + H 2 O(l) > Ca(HCO 3 ) 2 (aq) RemovalBoiling the water reverses the above reaction. A white precipitate of insoluble calcium carbonate is produced. The calcium is thus removed from the water. Ca(HCO 3 ) 2 (aq) > CaCO 3 (s) + CO 2 (g) + H 2 O(l) plusAny method used for removing permanent hardness. REMEMBER Only water containing SOLUBLE calcium and magnesium ions causes hardness. REMEMBER Only water containing SOLUBLE calcium and magnesium ions causes hardness.

30 TEMPORARY HARDNESS SourceAtmospheric carbon dioxide dissolves in rain water making an acidic solution which reacts with limestone (calcium carbonate). Soluble calcium hydrogencarbonate is formed. CaCO 3 (s) + CO 2 (g) + H 2 O(l) > Ca(HCO 3 ) 2 (aq) RemovalBoiling the water reverses the above reaction. A white precipitate of insoluble calcium carbonate is produced. The calcium is thus removed from the water. Ca(HCO 3 ) 2 (aq) > CaCO 3 (s) + CO 2 (g) + H 2 O(l) plusAny method used for removing permanent hardness. REMEMBER Only water containing SOLUBLE calcium and magnesium ions causes hardness. REMEMBER Only water containing SOLUBLE calcium and magnesium ions causes hardness.

31 PERMANENT HARDNESS

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

33 PERMANENT HARDNESS SourceSoluble calcium and magnesium compounds which dissolve in streams and rivers as they pass over and through rocks and soils. SOLUBLEcalcium chloride CaC l 2 magnesium chloride MgC l 2 magnesium sulphate MgSO 4 INSOLUBLEcalcium carbonate CaCO 3 magnesium carbonate MgCO 3

34 PERMANENT HARDNESS SourceSoluble calcium and magnesium compounds which dissolve in streams and rivers as they pass over and through rocks and soils. SOLUBLEcalcium chloride CaC l 2 magnesium chloride MgC l 2 magnesium sulphate MgSO 4 INSOLUBLEcalcium carbonate CaCO 3 magnesium carbonate MgCO 3 REMEMBER Only water containing SOLUBLE calcium and magnesium ions causes hardness. 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. HARD WATER PURE WATER CONDENSER

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 Ca 2+ and Mg 2+ ions in the hard water swap with those on the resin The water comes out with Na + ions in it Ca 2+ and Mg 2+ ions remain attached to the resin Na + and H + ions do not cause hardness. Ca 2+ (aq) + 2Na + > Ca Na + (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. 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) Hard water contains soluble calcium (or magnesium) ions. Sodium carbonate is one of the few soluble carbonates - it is a good source of soluble carbonate ions.

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

50 PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate) The Ca 2+ and CO 3 2- ions come together to form a precipitate of insoluble calcium carbonate. The calcium ions are removed from the water so it is now soft.

51 PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate) - SUMMARY Sodium carbonate is one of the few soluble carbonates - it is a good source of soluble carbonate ions. Addition of washing soda to a solution containing magnesium ions or calcium ions results in the precipitation of insoluble carbonates. Once the magnesium, or calcium, has been removed from the water, the water is no longer hard - it is soft. equationCaC l 2 (aq) + Na 2 CO 3 (aq) > 2NaC l (aq) + CaCO 3 (s) ionic equation Ca 2+ (aq) + CO 3 2- (aq) > Ca 2+ CO 3 2- (s)

52 HARD WATER Disadvantages Furring up of pipes and boilers; the heating is not as effective blockages may lead to an explosion

53 HARD WATER Disadvantages Furring up of pipes and boilers; the heating is not as effective blockages may lead to an explosion Furring up of kettle elements;wastes electricity

54 HARD WATER Disadvantages Furring up of pipes and boilers; the heating is not as effective blockages may lead to an explosion Furring up of kettle elements;wastes electricity Wastes soap;as some is needed to remove the hardness unsightly scum is formed during washing

55 HARD WATER Disadvantages Furring up of pipes and boilers; the heating is not as effective blockages may lead to an explosion Furring up of kettle elements;wastes electricity Wastes soap;as some is needed to remove the hardness unsightly scum is formed during washing Advantagescalcium strengthens teeth and bones. better for preventing heart diseases

56 WATER POLLUTION

57 Originnitrates and phosphates in farm fertilizers animal waste products industrial chemical waste lead ions (Pb 2+ ) from old pipes

58 WATER POLLUTION Originnitrates and phosphates in farm fertilizers animal waste products industrial chemical waste lead ions (Pb 2+ ) from old pipes EffectsNitrates from fertilizers encourage plant and algae growth. When algae die they are decomposed by aerobic bacteria which need oxygen. The oxygen is thus removed from the water making the river dead and incapable of supporting fish populations. Nitrates can also be converted to nitrites (which affect haemoglobin in blood) and into carcinogenic nitrosamines. Industrial waste can be in many forms including cyanide, detergents and heavy metals and radioactive products. A build up of lead can lead to brain damage.

59 WATER POLLUTION Originnitrates and phosphates in farm fertilizers animal waste products industrial chemical waste lead ions (Pb 2+ ) from old pipes EffectsNitrates from fertilizers encourage plant and algae growth. When algae die they are decomposed by aerobic bacteria which need oxygen. The oxygen is thus removed from the water making the river dead and incapable of supporting fish populations. Nitrates can also be converted to nitrites (which affect haemoglobin in blood) and into carcinogenic nitrosamines. Industrial waste can be in many forms including cyanide, detergents, heavy metals and radioactive products. A build up of lead can lead to brain damage.

60 WATER PURIFICATION

61 Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes.

62 WATER PURIFICATION Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. Filtrationremoves insoluble organic matter; the sludge is digested to produce methane. Aerationremoves organic waste using oxygen-requiring bacteria. Chlorinationkills bacteria to allow water to be used for drinking purposes.

63 WATER PURIFICATION Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. Filtrationremoves insoluble organic matter; the sludge is digested to produce methane. Aerationremoves organic waste using oxygen-requiring bacteria. Chlorinationkills bacteria to allow water to be used for drinking purposes. IT CAN THEN BE SENT TO HOUSES THROUGH THE MAINS

64 WATER PURIFICATION Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. Filtrationremoves insoluble organic matter; the sludge is digested to produce methane. Aerationremoves organic waste using oxygen-requiring bacteria. Chlorinationkills bacteria to allow water to be used for drinking purposes. OTHER THINGS THAT CAN BE DONE FluoridationFluoride compounds are added to water in some areas to aid the prevention of tooth decay. The fluoride is only helpful to children and can be given in tablet form. Many people object to the addition of fluoride to drinking water.

65 WATER PURIFICATION Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. Filtrationremoves insoluble organic matter; the sludge is digested to produce methane. Aerationremoves organic waste using oxygen-requiring bacteria. Chlorinationkills bacteria to allow water to be used for drinking purposes. OTHER THINGS THAT CAN BE DONE FluoridationFluoride compounds are added to water in some areas to aid the prevention of tooth decay. The fluoride is only helpful to children and can be given in tablet form. Many people object to the addition of fluoride to drinking water. Water filters These contain carbon, silver and ion exchange resins and can remove some dissolved substances from tap water to improve the taste and quality.

66 WATER PURIFICATION Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. Filtrationremoves insoluble organic matter; the sludge is digested to produce methane. Aerationremoves organic waste using oxygen-requiring bacteria. Chlorinationkills bacteria to allow water to be used for drinking purposes. OTHER THINGS THAT CAN BE DONE FluoridationFluoride compounds are added to water in some areas to aid the prevention of tooth decay. The fluoride is only helpful to children and can be given in tablet form. Many people object to the addition of fluoride to drinking water. Water filters These contain carbon, silver and ion exchange resins and can remove some dissolved substances from tap water to improve the taste and quality. DistillationNeeds a lot of energy so is expensive but makes the purest water.

67 © 2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHING WATER THE END


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