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SS3: CHEMISTRY - 2ND TERM

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  1. Quality of Petrol (Octane Number)| Week 1
    1 Topic
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    1 Quiz
  2. Natural Gas | Week 2
    3 Topics
    |
    1 Quiz
  3. Introduction to Metals | Week 3
    3 Topics
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    1 Quiz
  4. The Alkali Metals | Week 4
    4 Topics
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    1 Quiz
  5. Alkaline Earth Metals | Week 5
    4 Topics
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    1 Quiz
  6. Aluminium & Tin | Week 6
    3 Topics
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    1 Quiz
  7. Transition Metals of the First Series | Week 7
    4 Topics
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    1 Quiz
  8. Ethical, Legal & Social Issues | Week 8
    3 Topics
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    1 Quiz
  9. Fats & Oils - Soaps & Detergents | Week 9
    4 Topics
  10. Giant Molecules | Week 10
    6 Topics



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sodium

Sodium: Occurrence:

Sodium is the eighth most abundant element by weight in the earth’s crust. NaCl occurs in large amount in oceans, salt lakes and seas. Rock salt (NaCl) is the major source of sodium. It also occurs as soda feldspar (NaAlSi3O8), borax (Na2[B4O5(OH)4]·8H2O), chile saltpeter (NaNO3) and Glauber’s salt Na2SO4.10H2O.

Extraction of Sodium (Downs Process):

Sodium metal is extracted by Down’s process. This involves the electrolysis of fused sodium chloride. The anode is graphite and the cathode is a ring shaped iron. The two electrodes are separated by a wire gauge partition to avoid the mixing of sodium and chlorine formed.

Due to high melting point of sodium chloride (about 800oC), a small amount of calcium chloride is added to the sodium chloride to lower its melting point to about 600oC.

Chlorine is liberated at the anode and escapes through the dome shaped steel hood outlet. 

\( \scriptsize 2Cl^-_{(aq)} \: \rightarrow \: Cl_{2(g)} ^+ \: + \: 2e^-_{(aq)} ….(reduction)\)

At the cathode, sodium ion is attracted to the electrode where they accept electrons and form sodium metal. 

\( \scriptsize 2Na^+_{(aq)} \: +\: 2e^-_{(aq)} \: \rightarrow \: 2Na_{(s)}….(oxidation) \)

Overall reaction

\( \scriptsize 2Na^+ \: + \: 2Cl^-\: \: \rightarrow \: 2Na^+_{(s)} \: + \: Cl_{2(g)} \)

Sodium metal being lighter than the electrolyte, floats on the surface of the molten NaCl and flows into a separate container.

downs cell
Extraction of Sodium (Downs Cell)

Advantages of Down’s Process:

1. Sodium metal obtained has high degree of purity (99.5%).
2. The raw material, sodium chloride is very cheap.

Physical Properties of Sodium:

i. Sodium is a silvery-white metal.

ii. It is quite malleable and soft.

iii. It is a good conductor of heat and electricity.

iv. Its melting point is 97°C.

v. It has the density of 0.97 g/cm3

Chemical Properties of Sodium:

i. In air, sodium is swiftly oxidized to sodium oxide.

4Na + O2 → 2Na2O

ii. Reaction of sodium with dilute acids

2Na + 2HCl →  2NaCl + H2(g)

iii. Reaction with water: Na reacts vigorously with water to liberate hydrogen gas 

2Na(s) + H2O → 2NaOH(aq) + H2(g)

iv. Reaction with ammonium gas: Sodium reacts with ammonia to form sodamide and hydrogen gas.

2Na + 2NH3 → 2NaNH2 + H2

v. Reaction with halogens: Sodium reacts with halogens to form salts.

2Na + Cl2 → 2NaCl 

2Na + Br2 → 2NaBr 

vi. Sodium reacts poorly with nitrogen to form sodium nitride.  

6Na + N2 → 2Na3N

Uses of Sodium:

sodium lamps
Sodium vapour lamps, often used for illuminating highways.

1. Sodium vapour lamps are used for lightening highways and airports.

2. Liquid sodium is used in nuclear reactors as a coolant.

3. Sodium is used in the manufacture of many compounds such as sodium peroxide, soda-lime, and sodium cyanide.

Sodium Peroxide
Sodium Peroxide.

4. It is a good reducing agent for some chemical processes, like the extraction of titanium.

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