Oxidation reduction reactions
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Oxidation - Reduction Reactions. a ka “Redox” corresponding to chapter 20 in text. Oxidation - Reduction reactions. Redox reactions involve Complete or partial transfer of electrons Change in oxidation numbers Oxidation numbers are pseudo charges. Rules for Oxidation Numbers.

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Oxidation - Reduction Reactions

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Oxidation reduction reactions

Oxidation - Reduction Reactions

aka “Redox” corresponding to chapter 20 in text


Oxidation reduction reactions1

Oxidation - Reduction reactions

  • Redox reactions involve

    • Complete or partial transfer of electrons

    • Change in oxidation numbers

      • Oxidation numbers are pseudo charges


Rules for oxidation numbers

Rules for Oxidation Numbers

  • Usually is the charge the atom would have if it was an ion

  • Monatomic ion = ionic charge

  • H is always 1+ unless bound to metal (1-)

  • O is always 2- unless in peroxide (1-)

  • Free elements are always 0 (HONClBrIF too)

  • Σ of neutral compounds constituent oxidation numbers = 0

  • Σ of polyatomic constituent oxidation numbers = charge


Assigning oxidation numbers

Assigning Oxidation Numbers

NaClOH2SO4

H2ONaCl

NaCrO2NaOH

H2O2Na2CrO4

OH-1 Ag

HNO3 AgNO3

NOCa(OH)2

Cl2CaCl2

Ca(ClO3)2KNO3


Leo the lion says ger

LEO the lion says GER

  • Can’t have a growl without a lion

    • Can’t have oxidation without reduction

    • Paired reaction


Leo the lion

LEO the lion…

  • L = Lose

  • E = Electrons

  • O = Oxidation

  • Oxidation: Loss of electrons


Leo the lion1

LEO the lion…

  • Fe+2 Fe+3 + e-

    • Oxidation number becomes more positive

    • Gained oxygen

    • Shifts electrons away


Says ger

…says GER

  • G = Gain

  • E = Electrons

  • R = Reduction

  • Reduction: Gain of electrons


Says ger1

…says GER

  • Fe+3 + e-  Fe+2

    • Oxidation number becomes more negative

    • Loss of oxygen

    • Shifts electrons towards


Why do lions growl

Why do Lions Growl?

  • Oxidation and reduction occur together

    • Why?

      • Presence of oxidizingand reducing agents


Agents

Agents

  • Oxidizing Agent

    • Substance that is being reduced

      • Hence, causing the oxidation

  • Reducing Agent

    • Substance that is being oxidized

      • Causing the reduction


Balancing redox reactions

Balancing Redox Reactions

  • 2 methods

    • Half reaction

      • (preferred by chemists)

    • Oxidation number change

      • (preferred by lazy students and can lead you astray)


Half reaction from book

Half Reaction (from book)


Half reaction basics

Half Reaction (basics)

  • Separate the equation into the oxidation portion and the reduction portion

  • Balance both separately for e- gained or lost

  • Multiply each ½ rxn to yield a balanced overall e- shift

  • Put coefficients back up into the original eq

  • Balance “spectators” for atoms


Try it

Try It!

  • Write the balanced redox reaction for the following:

  • Na(s) + FeCl2(aq)  NaCl(aq) + Fe(s)


Oxidation number change method

Oxidation Number Change Method

  • Step 1: assign oxidation numbers

  • Step 2: ID atoms being oxidized and reduced

  • Step 3: use brackets to connect the oxidation (loss of e-) and reduction (gain in e-)


Same eq but using ox number change method

Same eq… but using ox number change method

0+2-1 +1 -1 0

  • Na(s) + FeCl2(aq)  NaCl(aq) + Fe(s)


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