oxidation reduction reactions n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Oxidation-Reduction Reactions PowerPoint Presentation
Download Presentation
Oxidation-Reduction Reactions

Loading in 2 Seconds...

play fullscreen
1 / 13

Oxidation-Reduction Reactions - PowerPoint PPT Presentation


  • 155 Views
  • Uploaded on

Oxidation-Reduction Reactions. Oxidation. Reactions in which the atoms or ions of an element attain a more positive (or less negative) oxidation state are oxidation processes. A species that undergoes a change in oxidation state in a positive direction is said to be oxidized .

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Oxidation-Reduction Reactions' - saskia


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
oxidation
Oxidation
  • Reactions in which the atoms or ions of an element attain a morepositive (or less negative) oxidation state are oxidation processes.
  • A species that undergoes a change in oxidation state in a positive direction is said to be oxidized.
  • Loss of electrons = oxidation
reduction
Reduction
  • Reactions in which the atoms or ions of an element attain a morenegative (or less positive) oxidation state are reduction processes.
  • A species that undergoes a change in oxidation state in a negative direction is said to be reduced.
  • Gain of electrons = reduction
mnemonic devices
Mnemonic Devices
  • Leo the Lion goes “ger”

Lose electrons = oxidation

Gain electrons = reduction

  • Oil Rig

Oxidation is loss (of electrons)

Reduction is gain (of electrons)

oxidation reduction reactions1
Oxidation-Reduction Reactions
  • A chemical process in which elements undergo a changeintheiroxidation number.
  • Called “redox” reactions for short.
  • Combines the two processes of reduction and oxidation into one equation.
oxidation numbers
Oxidation Numbers
  • We assign oxidation numbers or oxidation states to atoms and ions within compounds to help us “see” the movement ofelectrons when we look at the species within a redox reaction.
  • We have rules for assigning these numbers.
assigning oxidation states p 655
Assigning Oxidation Statesp. 655
  • The oxidation state of an atom in an uncombined element is 0.
  • The oxidation state of a monatomic ion is the same as its charge.
  • Oxygen is assigned an oxidation state of -2 in most of its covalent compounds. (Important exception: peroxides; in these oxygen has an oxidation state of -1.)
  • In its covalent compounds with nonmetals, hydrogen is assigned an oxidation state of +1. (When hydrogen combines with metals in a hydride, the hydrogen has an oxidation state of -1.)
  • In binary covalent compounds (2 nonmetals), the element with the greater electronegativity is assigned a negative oxidation state equal to its charge as an anion in its ionic compounds.
  • For an electrically neutral compound, the sum of the oxidation states must be zero.
  • For an ionic species, the sum of the oxidation states must equal the overall charge.
redox reactions
Redox Reactions

2 Na (s) + Cl2 (g)  2 NaCl (aq)

0 0 +1 -1

Na goes from 0 to +1 (hence gives away 1 electron) so it is oxidized

Cl goes from 0 to -1 (hence gets 1 electron) so it is reduced

half reactions
Half Reactions
  • Half Reactions divide a redox reaction into two parts: one that shows oxidation and one that shows reduction
  • Half Reactions also show the transfer of electrons.
  • Oxidation Half Reaction shows loss of electrons so they are shown as products.
  • Reduction Half Reaction shows gain of electrons so they are shown as reactants.
half reactions for synthesis of table salt
Half Reactions for synthesis of table salt

2 Na (s) + Cl2 (g)  2 NaCl (aq)

0 0 +1 -1

Ox. H.R. : 2 Na  2 Na+1 + 2 e-

Red. H.R.:Cl2 + 2 e-  2 Cl-

terminology
Terminology
  • The substance that loses electrons is said to be oxidized; we can also call it the reducing agent (because it causes the other substance in the equation to be reduced).
  • The substance that gains electrons is said to be reduced; we can also call it the oxidizing agent (because it causes the other substance to be oxidized).
slide12
2 Na (s) + Cl2 (g)  2 NaCl (aq)

0 0 +1 -1

Ox. H.R. : 2 Na  2 Na+1 + 2 e-

Red. H.R.:Cl2 + 2 e-  2 Cl-

So, in our example above,

sodium is oxidized and is the reducing agent; chlorine is reduced and is the oxidizing agent.

practice
Practice

3 Mg (s) + Al2(SO4)3(aq) 2 Al (s) + 3 MgSO4(aq)

0 3+ 6+ 2- 0 2+ 6+ 2-

Mg: 0 to 2+ Al: 3+ to 0 S and O: no change

loses e-, so oxidized gains e- , so reduced

Ox. H.R. : 3 Mg0 3 Mg2+ + 6 e-

Red. H.R.: 2 Al3+ + 6 e-  2 Al0

So,

Mgis oxidized and is the reducingagent;

Alis reduced and is the oxidizingagent.