11: Oxidation-Reduction reactions Flashcards Preview

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Flashcards in 11: Oxidation-Reduction reactions Deck (19):

law of conservation of charge

states that electrical charge can be neither created nor destroyed... so oxidation (loss of electrons) must occur simultaneously with reduction (gain of electrons)


redox reaction

electron transfer involving oxidation and reduction


oxidizing agent

causes another atom to be oxidized and itself reduced

*the term ox/red agent is applied specifically to the atom that loses/gains electrons, but often compound as a whole is described as oxidizing or reducing agent (ie. CrO3 is compound described as oxidizing agent but Cr6+ is the actual oxidizing agent part 


reducing agent

causes another atom to be reduced and itself oxidized


common oxidizing agents

O2, H2O2

halogens: F2, Cl2, Br2, I2

H2SO4, HNO3, NaClO, KMnO4

CrO3, Na2Cr2O7



common reducing agents

CO, C, B2H6

Sn2+ and other pure metals

Zn(Hg), hydrazine, Lindlar's catalysts



biochemical redox agents

such as NAD+ and FADH act as both oxidizing and reducing agents at different times during metabolic pathways... thus they act as mediators of energy transfer during many metabolic processes


oxidation numbers 

are assigned to atoms in order to keep track of the redistributionof electrons during chemical reactions... think of ox numbers as the typical charge of an element

*assumes unequal division of electrons in bonds UNLIKE formal charge, which asumes equal division

*conventions put cation first and anion second so HCl implies H+ and NaH implies H-


assigning oxidtion numbers

  1. ox number of a free element is 0
  2. ox number for a monoatomic ion is equal to the charge of the ion
  3. group 1A elements is +1
  4. group 2A elements is +2
  5. group VIIA element is -1 except when combined witha more electronegative element
  6. hydroen is usually +1 except whenit is with less electronegative elements
  7. oxygen is usually -2 except in peroxides and compounds with more electronegative elements
  8. sum of ox numbers of all atoms in a neutral compound is 0... equals charge in polyatomic ion


half-reaction method/ion-electron method

equation is separated into 2 half-reactions (oxidation part and the reduction part) and each half-reaction is balanced seperately and then added to give overall reaction

  • add H2O and then Hto balance acidic solution
  • add OH- and H20 to balance basic solution
  • then add electrons to balance charges
  • then cancel out lectrons and terms that appear on both sides


complete ionic equations

split various species into all the ions present including spectator ions


net ionic equations

does not involve spectator ions

  • all aquoeous compounds should be split into their consituent ions
  • solid salts should be kept together as a single entity


comibination reactions

2+ species come together to form a product

ex. H2 (g) + F2 (g) → 2HF

net ionic is H2 (g) + F2 (g) → 2H+ + 2F-


decomposition reactions

one product breaks down into 2+ species

ex. (NH4)2Cr2O7 → N2 + Cr2O3 + 4H2O

net ionic: 2NH4+ + Cr2O72- → N2 + Cr2O3 + 4H2O


combustion reactioins

feul (hydrocarbon) is mixed with an oxidant (oxygen) forming CO2 and H2O

ex. CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l)

*net ionic equation is identical to the overall balanced equation because there are no spectator ions nd no aqueous species


double-displacement/methathesis reactions

involve switching of counterionsa

ex. AgNO3 (aq) + HCl (aq) → HNO3 (aq) + AgCl (aq)

net ionic: Ag+ + Cl- → AgCl

*not ox-red because all species retain same oxidation numbers


disproportionation reactions

specific type of redox reaction in which an element undergoes both oxidation and reduction in producing its products... usually uses enzymes

  • example is catalysis of peroxides by catalase, which is a critical biological enzyme
    • 2H2O2 (aq) → 2H2O (l) + O2 (g)


oxidation-reduction titrations

follow transfer of charge (electrons) to reach equivalence point rather than movement of protons in acid-base 

  • use indicators that change color at particular voltage (emf) value
  • ex. iodimetric titration which relies on titration of free iodine radicals 


potentiometric titration

form of redox titration where no inidcator is used... instead a voltemeter is used to measure electrical potential difference (voltage)

*analagous to using pH meter for acid base titration