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SS2: CHEMISTRY - 1ST TERM

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  1. Periodicity and Periodic Table I | Week 1
    5 Topics
    |
    1 Quiz
  2. Quantum Numbers Orbitals & Electrical Structure | Week 2
    6 Topics
    |
    1 Quiz
  3. Periodicity and Periodic Table II | Week 3
    12 Topics
    |
    1 Quiz
  4. Periodicity and Periodic Properties III | Week 4
    11 Topics
    |
    1 Quiz
  5. Periodicity and Periodic Properties IV | Week 5
    5 Topics
    |
    1 Quiz
  6. Mass-Volume Relationship in Reaction | Week 6
    8 Topics
    |
    1 Quiz
  7. Types of Reactions: Oxidation and Reduction | Week 7 & 8
    7 Topics
    |
    1 Quiz
  8. Oxidation – Reduction Reaction II | Week 9
    3 Topics
    |
    1 Quiz
  9. Electrode Potential and Electrochemical Cells I | Week 10
    6 Topics
    |
    1 Quiz
  10. Electrode Potential and Electrochemical Cells II | Week 11
    5 Topics
    |
    1 Quiz
  11. Electrolysis I | Week 12
    8 Topics
    |
    1 Quiz
  12. Electrolysis II | Week 13
    8 Topics
    |
    1 Quiz
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Topic Content:

  • Corrosion as an Electrochemical Process

Corrosion is the conversion of metals into their oxide as a result of contact with moisture and air. The corrosion of iron is known as rusting

Iron rusts when it comes into contact with air and water because electrochemical cells are set up at the surface of contact.

At the anode (Anodic region)

Metallic iron is oxidized to give Iron(II) ions 

Fe(s) →  Fe2+(aq) + 2e

At the cathode (Cathodic Region)

Oxygen from the air is dissolved in water since oxygen concentration in water is higher. The oxygen is reduced by the electrons from the anode to hydroxide ion OH

\( \frac{1}{2} \scriptsize O_{2(aq)} \: + \: H_2O_{(l)} \: + \: 2e^- \: \rightarrow\: 2OH^-_{(aq)} \)

The Fe2+(aq) from the anodic region combine with OH(aq) from the cathodic region to form iron(II) hydroxide [(Fe(OH)2]

Fe2+(aq) + 2OH(aq) →   Fe(OH)2

Fe(OH)2 undergoes further oxidation with oxygen to form brown hydrated iron(III) oxide, Fe2O3.xH2O, or rust.

\( \scriptsize \underset{Iron(II)\: hydroxide}{4Fe(OH)_2} \: + \: \underset{oxygen}{O_2} \: \rightarrow \: \underset{hydrated \: Iron(III)\: oxide}{2Fe_2O_3.4H_2O} \)

Rust is soft and breaks off easily and the metal below continues to rust.

The essential conditions for rusting are moisture and oxygen (air) which act together on iron.

There are many preventive methods against the rusting of iron. The basic principle of the method is the prevention of water and air from coming into direct contact with iron.