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. 4.2 COMPOSITION OF SEA WATER
magnesium
chloride 14.6%
______________
common salt
(sodium chloride) 68%
sodium
sulphate 11.4%
calcium
chloride 3.1%
other salts 2.9%
Figure 4.2 The 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 4.3 Common 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
salt
Figure 4.5 Common salt can be obtained from sea water by evaporation.
4.3 Extraction of common salt from sea water

9. (b) Heating with a steam-bath
sea water
evaporating
basin
sea water
steam
evaporating
basin
water
wire gauze
heat
tripod
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. + 1. Filtration Pure sodium chloride 2. Crystallization
TO OBTAIN PURE SODIUM CHLORIDE
1. Filtration
Pure sodium
chloride +
2. Crystallization
4.3 Extraction of common salt from sea water

11. Filtration 1. Pour sea water onto filter paper
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 filter funnel filter paper fold
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 4.8 Filtration 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 Crystallization from sea water by slow evaporation.
4.3 Extraction of common salt from sea water

17. How to obtain pure water from sea water?
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. end of delivery tube should be above distillate receiver test tube
pure water
(distillate)
end of delivery tube should be
above distillate
receiver test tube
delivery tube
water (cooling agent)
heat
anti-bumping granule (to prevent ‘bumping’ of solution)
sea water
boiling tube
clamp
thermometer
Figure 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 The desalting plant at Lok On Pai had been sold to a foreign country.
4.3 Extraction of common salt from sea water

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

24. (brilliant golden yellow)
potassium
(lilac)
sodium
(brilliant golden yellow)
calcium
(brick red)
copper
(bluish green)
Figure 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. TEST FOR CHLORIDE IONS add silver nitrate solution followed by
sea water
white precipitate of silver chloride
add silver nitrate solution followed by
excess dilute nitric acid
Figure Silver nitrate test for the presence of chloride ions.
4.4 Tests for sodium and chloride ions in common salt

27. Water present? 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. Water turns white anhydrous copper(II) sulphate blue.
watch glass
add a few drops of water
water
anhydrous copper(ll) sulphate
Figure 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. Water turns blue cobalt chloride test paper pink.
in the presence of water
test paper turns pink
Blue cobalt chloride test paper
Figure 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. ELECTROLYSIS Decomposition by electricity
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. Sea water chlorine sodium hydroxide hydrogen For example electrolysis
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. Figure 4.22 Some uses of products from the electrolysis of brine.
Hydrogen
Chlorine
Sodium
hydroxide
HCl
hydrochloric acid
solvents
treatment of acidic effluents from factories
ammonia (used to make fertilizers)
aluminium extraction
MARGARINE
food industry
bleach
water treatment for sanitation
rocket fuel
soap
HCl
hydrochloric acid
paper making
plastic (e.g. PVC)
chemicals (e.g. dyes & pesticides)
Figure 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 the residue.
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. Sodium hydroxide
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. WATER Salts Sodium chloride Others Cobalt chloride test paper /
68%
32%
tested with
distillation
Sodium
chloride
Others
Cobalt chloride
test paper /
____________
Pure water
anhydrous
copper(II)
sulphate
Concept map

44. ________ 1. filtration 2. crystallization ______ sodium chloride
evaporation
______ sodium
chloride
Pure
Impure sodium
chloride
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