CHEMISTRY FORM 4

TOPIC: METALS

SUB-TOPIC: EXTRACTION OF SODIUM METAL.

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FORM 2

SPECIFIC LESSON OBJECTIVES

By the end of the lesson you should be able to:

1. Name the ores of sodium.
2. Describe the extraction of sodium.

ORES OF SODIUM�

CONFIRMATION OF THE METAL ION IN THE ORE �

• Add water to a portion of the ore (all sodium salts are soluble) and stir, filter to remove undissolved impurities.

Flame test

• Dip a glass rod or Nichrome wire into the filtrate and burn it at the tip of a non-luminous flame.
• Yellow flame confirms presence of Na⁺ ions

• It is extracted through the downs cell process.
• Sodium is extracted by electrolysis of the fused sodium chloride.

Most used ore is rock salt because

• it is the most abundant.
• It also requires very little purification

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EXTRACTION OF SODIUM

• Sodium chloride is fed into the down cell and heated strongly to melt it. A little CaCl₂ is added to lower the melting point from 801 to 600^oC to lower the fuel cost.

EXTRACTION OF SODIUM

EXTRACTION OF SODIUM

• The electrolyte is molten sodium chloride; high current of about 30,000ampheres is passed through the electrolyte to:
• Decompose the ore .
• maintain the ore in liquid state due to resistance.
• Chlorine gas is liberated at the graphite anode while molten sodium is formed at the steel cathode.

EXTRACTION OF SODIUM

Points to note.

• Graphite is the most suitable substance to be used as anode because it is inert and does not react with chlorine gas even at high temperature.
• Role of the hood; collects chlorine gas and channels it out, where it is trapped to prevent it from being released to the atmosphere as it is poisonous gas and hazardous to environment.

• A steel diaphragm is suspended between the cathode and anode to prevent the sodium and chlorine formed from recombining at this high temperature.
• The steel cathode does not melt as its melting point is higher than that of NaCl and sodium metal.

Points to note.

• The downs cell is surrounded by iron wall filled with fire bricks forming heat resistant wall, its purpose it to maintain the high temperatures the so that the electrolyte does not crystallize .

Points to note.

state two reasons why sodium preferably

discharged instead of calcium at the cathode

• Sodium ions are lower in the electrochemical series than calcium ions.

• Sodium ions have higher concentration in the electrolyte than calcium ions.

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Points to note.

At cathode; sodium ions are discharged to form molten sodium

At anode; Chloride ions are discharged to form chlorine gas which escapes via the wood.

Molten sodium is less denser then the electrolyte hence rises to the top of cathode where is periodically removed

Equations at the electrodes .

• Sodium metal obtained has high degree of purity (99.5%).
• The starting material, sodium chloride is very cheap.
• Chlorine is obtained as a useful by-product.

Advantages of down's process

.State two properties of sodium that make it

possible to be separated from the electrolyte

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• Less denser than molten sodium chloride.
• Has lower melting point than molten sodium chloride.

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Revision exercise

State and explain pollution effect associated with extraction of sodium metal.

Assignment.