SS2: CHEMISTRY - 1ST TERM
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Periodicity and Periodic Table I | Week 15 Topics|1 Quiz
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Quantum Numbers Orbitals & Electrical Structure | Week 26 Topics|1 Quiz
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Periodicity and Periodic Table II | Week 312 Topics|1 Quiz
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Periodic Table and Atomic Properties
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Melting and Boiling Point
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Electrical and Thermal Conductivities
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Atomic Size [Radius]
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Ionic Size [Radius]
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Atomic Volume
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Ionization Energy
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Electron Affinity
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Electronegativity
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Differences between Ionization Energy and Electron Affinity
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Summary of Trends of Atomic Properties
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Theory Questions - Periodicity and Periodic Table II
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Periodic Table and Atomic Properties
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Periodicity and Periodic Properties III | Week 411 Topics|1 Quiz
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Periodicity and Periodic Properties IV | Week 55 Topics|1 Quiz
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Mass-Volume Relationship in Reaction | Week 68 Topics|1 Quiz
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Types of Reactions: Oxidation and Reduction | Week 7 & 87 Topics|1 Quiz
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Oxidation – Reduction Reaction II | Week 93 Topics|1 Quiz
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Electrode Potential and Electrochemical Cells I | Week 106 Topics|1 Quiz
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Electrode Potential and Electrochemical Cells II | Week 115 Topics|1 Quiz
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Electrolysis I | Week 128 Topics|1 Quiz
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Electrolysis II | Week 138 Topics|1 Quiz
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 anodeAn anode is an electrode of a polarized electrical device through which conventional current enters the device. It is the positive part of electrolytes where oxidation takes place. More (Anodic region)
Metallic iron is oxidized to give Iron(II) ions
Fe(s) → Fe2+(aq) + 2e–
At the cathodeA cathode is the electrode from which a conventional current leaves the electrolyte. It is the negative part of the cell where reduction takes place. More (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.