Chapter 4 Oceans

1. Chapter 4 Oceans Chapter 4 Oceans 4.1 Introducing oceans and seas 4.2 Composition of sea water 4.3 Extraction of common salt from sea water 4.4 Tests for sodium and chloride ions in common salt 4.5 Tests for the presence of water in a sample 4.6 Electrolysis of sea water and uses of products Summary Concept map Chapter 4 Oceans

2. OCEANS SEAS 4.1 INTRODUCING OCEANS AND SEAS Large area of salty water Covers the Earth’s surface Enclosing its continents and islands 4.1 Introducing oceans and seas

3. 70% of it is covered by water and 97% of this water occurs in oceans and seas! Figure 4.1 The Earth is the ‘water planet’ in our solar system. 4.1 Introducing oceans and seas

4. common salt (sodium chloride) 68% 4.2 COMPOSITION OF SEA WATER magnesium chloride 14.6% ______________ ______________ sodium sulphate 11.4% calcium chloride 3.1% other salts 2.9% Figure 4.2The salt composition by weight of a typical sea water sample. 4.2 Composition of sea water

5. 4.3 EXTRACTION OF COMMON SALT FROM SEA WATER Common salt (sodium chloride) is the most abundant resource in sea water. 4.3 Extraction of common salt from sea water

6. Figure 4.3Common salt is the most important natural flavouring. 4.3 Extraction of common salt from sea water

7. Figure 4.4 Many useful chemicals can be obtained from common salt in chlor-alkali industry. 4.3 Extraction of common salt from sea water

8. EVAPORATION OF SEA WATER Evaporation salt Figure 4.5 Common salt can be obtained from sea water by evaporation. 4.3 Extraction of common salt from sea water

9. sea water evaporating basin sea water steam evaporating basin water wire gauze tripod heat heat (a) Direct heating (b) Heating with a steam-bath Figure 4.6 Getting common salt from sea water in the laboratory. 4.3 Extraction of common salt from sea water

10. TO OBTAIN PURE SODIUM CHLORIDE 1. Filtration Pure sodium chloride + 2. Crystallization 4.3 Extraction of common salt from sea water

11. Filtration Firstly, any insoluble substances such as sand should be removed from sea water by filtration. 1. Pour sea water onto filter paper 2. Use a glass rod to guide the flow 3. Small particles pass through as filtrate 4. Larger insoluble particles are retained as residue 4.3 Extraction of common salt from sea water

12. one layer three layers fold fold filter funnel filter paper Figure 4.7 A piece of filter paper is folded into a conical shape and placed in a funnel. 4.3 Extraction of common salt from sea water

13. glass rod sea water folded filter paper residue filter funnel filtrate Figure 4.8Filtration of sea water. stand 4.3 Extraction of common salt from sea water

14. Filtration of sea water. 4.3 Extraction of common salt from sea water

15. Crystallization After the removal of insoluble impurities, pure crystals of common salt can be separated out by crystallization. 1. Evaporate slowly at room temperature 2. Solution becomes more concentrated 3. Solution becomes saturated 4. Solid crystals slowly grow in size 4.3 Extraction of common salt from sea water

16. solution saturated with respect to sodium chloride sea water more concentrated solution sodium chloride crystals Water slowly evaporates at room temperature Figure 4.10 Crystallization from sea water by slow evaporation. 4.3 Extraction of common salt from sea water

17. ISOLATION OF PURE WATER FROM SEA WATER How to obtain pure water from sea water? By Distillation 4.3 Extraction of common salt from sea water

18. Distillation involves boiling of a solution followed by condensation of the vapour formed. 4.3 Extraction of common salt from sea water

19. thermometer clamp boiling tube delivery tube sea water receiver test tube heat end of delivery tube should be above distillate anti-bumping granule (to prevent ‘bumping’ of solution) water (cooling agent) pure water (distillate) Figure 4.11 Distillation of sea water using simple apparatus. 4.3 Extraction of common salt from sea water

20. Distillation of sea water (copper(II) sulphate solution) using simple apparatus. 4.3 Extraction of common salt from sea water

21. To obtain fresh water from sea water on a large scale Figure 4.13 The desalting plant at Lok On Pai had been sold to a foreign country. 4.3 Extraction of common salt from sea water

22. 4.4 TESTS FOR SODIUM AND CHLORIDE IONS IN COMMON SALT CHEMICAL ANALYSIS Composition Identification 4.4 Tests for sodium and chloride ions in common salt

23. non-luminous flame flame colour due to metal ions concentrated hydrochloric acid sample of the salt to be tested platinum wire (b) (a) (c) TEST FOR SODIUM IONS Figure 4.15 Performing a flame test to identify metal ions in a sample. 4.4 Tests for sodium and chloride ions in common salt

24. potassium (lilac) sodium (brilliant golden yellow) calcium (brick red) copper (bluish green) Figure 4.16 Flame colours of some metal ions. 4.4 Tests for sodium and chloride ions in common salt

25. Sodium compounds give a brilliant golden yellow flame in the flame test. Calcium compounds give a brick red colour. 4.4 Tests for sodium and chloride ions in common salt

26. sea water white precipitate of silver chloride TEST FOR CHLORIDE IONS add silver nitrate solution followed by excess dilute nitric acid Figure 4.17 Silver nitrate test for the presence of chloride ions. 4.4 Tests for sodium and chloride ions in common salt

27. 4.5 TESTS FOR THE PRESENCE OF WATER IN A SAMPLE Anhydrous copper(II) sulphate powder Water present? Dry cobalt chloride test paper 4.5 Tests for the presence of water in a sample

28. watch glass add a few drops of water water anhydrous copper(ll) sulphate Figure 4.18 Water turns white anhydrous copper(II) sulphate blue. Water turns white anhydrous copper(II) sulphate blue. 4.5 Tests for the presence of water in a sample

29. test paper turns pink in the presence of water Blue cobalt chloride test paper Figure 4.19 Water turns blue cobalt chloride test paper pink. Water turns blue cobalt chloride test paper pink. 4.5 Tests for the presence of water in a sample

30. 4.6 ELECTROLYSIS OF SEA WATER AND USES OF PRODUCTS ELECTROLYSIS Decomposition by electricity 4.6 Electrolysis of sea water and uses of products

31. electrolysis For example chlorine sodium hydroxide Sea water hydrogen 4.6 Electrolysis of sea water and uses of products

32. Figure 4.21 Membrane cells in ICI chlor-alkali plant in Malaysia. 4.6 Electrolysis of sea water and uses of products

33. Q4.1 In the chlor-alkali industry, brine, but not sea water, is electrolysed. Explain why. 4.6 Electrolysis of sea water and uses of products

34. A4.1 Both brine and sea water are a concentrated solution of sodium chloride. Brine is prepared by dissolving rock salt (sodium chloride) in water, so it does not contain other salts. Sea water is natural. Besides sodium chloride, it contains other dissolved salts as well. It is more suitable to electrolyse brine in chlor-alkali industry, since the concentration of sodium chloride can be increased to a high level as desired. 4.6 Electrolysis of sea water and uses of products

35. Sodium hydroxide Hydrogen Chlorine hydrochloric acid HCl MARGARINE solvents treatment of acidic effluents from factories food industry ammonia (used to make fertilizers) water treatment for sanitation aluminium extraction HCl bleach paper making plastic (e.g. PVC) chemicals (e.g. dyes & pesticides) hydrochloric acid rocket fuel soap Brine electrolysis Figure 4.22 Some uses of products from the electrolysis of brine. 4.6 Electrolysis of sea water and uses of products

36. Summary Composition of sea water 1. Sea water contains about 3.5% by weight of dissolved substances. The main solute in sea water is common salt (sodium chloride). Obtaining common salt and pure water from sea water 2. Pure common salt can be extracted from sea water by filtration and crystallization. 3. Pure water can be isolated from sea water by distillation. Summary

37. 4. Distillation involves boiling of a solution followed by condensation of the vapour formed. 5. During distillation, the pure liquid that distils over is called the distillate; the solid left behind is called theresidue. Summary

38. Test for sodium ions 6. Some metals can be identified by the flame test. Some characteristic flame colours are: Summary

39. Test for chloride ions 7. To test for chloride ions in sea water, we add silver nitrate solution, acidified with excess dilute nitric acid, to a sample. A white silver chloride precipitate forms if chloride ions are present. Summary

40. Test for water 8. Anhydrous copper(II) sulphate and dry cobalt chloride test paper can be used to detect the presence of water in a given sample. Summary

41. Electrolysis of brine 9. Electrolysis of brine produces useful chemicals: hydrogen, chlorine and sodium hydroxide. Refer to Figure to 4.22 for their uses. Summary

42. Concept map Complete the following concept map. Uses:  food industry  hydrochloric acid  rocket fuel Uses:  water treatment  plastic  bleach Uses:  paper making  aluminium  soap Sodium hydroxide Hydrogen Chlorine electrolysis Sea water Concept map

43. anhydrous copper(II) sulphate WATER Salts distillation tested with 68% 32% Sodium chloride Others Cobalt chloride test paper / ____________ ____________ ____________ Pure water Concept map

44. 1. filtration 2. crystallization ________ evaporation ______ sodium chloride Impure sodium chloride Pure consists of _______ ion _______ ion Sodium Chloride tested with acidified ____________ flame test silver nitrate Brilliant ___________ flame White precipitate golden yellow Concept map

45. END Chapter 4 Oceans