Oxidation and Reduction Reactions

Redox reactions involve transfer of electrons. In these reactions, one substance gets reduced (gains electrons) and the other gets oxidized (loses electrons).

  • Reduction: Gain of electrons, resulting in a lower oxidation state.

  • Oxidation: Loss of electrons, resulting in a higher oxidation state.

    Mnemonics to remember:

  1. LEO the lion goes GER: Lose Electrons Oxidation, Gain Electrons Reduction

  2. OIL RIG: Oxidation Is Loss, Reduction Is Gain.

    Real-Life Examples:

  • Silver Tarnishing: Silver spoons turn black when they react with hydrogen sulfide in the air. Silver atoms lose electrons and form silver sulfide, causing tarnish. The reaction is 2Ag+H2S<br>ightarrowAg2S+H22Ag + H2S <br>ightarrow Ag2S + H2.

  • Metal Purification: To purify copper, we add electrons to copper ions from its ores, turning them into pure copper

Examples of Reactions:

  • Oxidation:

    • Fe<br>ightarrowFe2++2e−Fe <br>ightarrow Fe^{2+} + 2e^{-}

    • 2Cl−<br>ightarrowCl2+2e−2Cl^{-} <br>ightarrow Cl_{2} + 2e^{-}

    • Fe2+<br>ightarrowFe3++e−Fe^{2+} <br>ightarrow Fe^{3+} + e^{-}

  • Reduction:

    • Cl2+2e−<br>ightarrow2Cl−Cl_{2} + 2e^{-} <br>ightarrow 2Cl^{-}

    • Na++e−<br>ightarrowNaNa^{+} + e^{-} <br>ightarrow Na

    • Fe3++e−<br>ightarrowFe2+Fe^{3+} + e^{-} <br>ightarrow Fe^{2+}

Practice Questions:

  • Be2+<br>ightarrowBeBe^{2+} <br>ightarrow Be: Reduction

  • P3−<br>ightarrowP2−P^{3-} <br>ightarrow P^{2-}: Oxidation

  • Na<br>ightarrowNa+Na <br>ightarrow Na^{+}: Oxidation

Half-Reactions:

  • Show either oxidation or reduction part of redox reactions.

  • Example of oxidation: Ag++e−<br>ightarrowAgAg^{+} + e^{-} <br>ightarrow Ag

  • Example of reduction: As+3e−<br>ightarrowAs3−As + 3e^{-} <br>ightarrow As^{3-}

Chemical Reactions and Agents:

  • In reactions, one part loses electrons (oxidation) and one gains electrons (reduction).

  • Example: 2Na+Cl2<br>ightarrow2NaCl2Na + Cl_{2} <br>ightarrow 2NaCl (Na oxidized, Cl reduced).

  • Sodium is the reducing agent, chloride is the oxidizing agent.

Reactivity of Metals:

  • Metals have different reactivities. Reactive metals are less stable.

  • Example: Gold is stable, does not corrode, whereas iron is reactive and rusts easily.

Spontaneity of Reactions:

  • A reaction is spontaneous if it happens without needing more energy.

  • For a spontaneous reaction, the reduction reaction should be above the oxidation reaction in activity series.

Non-Spontaneous Reactions:

  • These reactions do not happen easily because they require more energy to proceed.

Understanding these concepts can help in predicting how substances will react in different situations.