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

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

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

4.2 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

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

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

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

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

(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

+ 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

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

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

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

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

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

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

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

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

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 4.11 Distillation of sea water using simple apparatus. 4.3 Extraction of common salt from sea water

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

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

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

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 4.15 Performing a flame test to identify metal ions in a sample. 4.4 Tests for sodium and chloride ions in common salt

(brilliant golden yellow) 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

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

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 4.17 Silver nitrate test for the presence of chloride ions. 4.4 Tests for sodium and chloride ions in common salt

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

Water turns white anhydrous copper(II) sulphate blue. 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

Water turns blue cobalt chloride test paper pink. in the presence of water test paper turns pink 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

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

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

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

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

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

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 4.22 Some uses of products from the electrolysis of brine. 4.6 Electrolysis of sea water and uses of products

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

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

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

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

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

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

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

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

________ 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

END Chapter 4 Oceans