Redox reactions
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Redox Reactions. What is oxidation? What is reduction?. What is REDOX?. chemical reactions in which atoms have their oxidation state changed family of reactions that are concerned with the transfer of electrons between species. Rusting is an example of a redox reaction. REDOX.

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Redox Reactions

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Redox reactions

Redox Reactions

What is oxidation?

What is reduction?


What is redox

What is REDOX?

  • chemical reactions in which atoms have their oxidation state changed

  • family of reactions that are concerned with the transfer of electrons between species

Rusting is an example of a

redox reaction.


Redox

REDOX

  • term comes from the two concepts of reduction and oxidation

  • Oxidation is the loss of electrons or an increase in oxidation state

  • Reduction is the gain of electrons or a decrease in oxidation state

  • Oxidation State = the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic


Assigning oxidation numbers

Assigning Oxidation Numbers

#1. All free, uncombined elements have oxidation number of 0.

  • Includes diatomic elements such as O2

#2. All monoatomic ions have the same oxidation # as the charge on the ion.

Mg = +2Cl = -1

#3. All combined Hydrogen has oxidation # = +1. (except hydrides)


Assigning oxidation numbers1

Assigning Oxidation Numbers

#4. All combined Oxygen has oxidation # = -2. (except peroxides)

#5. Polyatomics = sum of oxidation numbers of elements in ion equals the charge on that species

Ex. Sulfate SO42¯

O = -2. There are four oxygens for -8 total.

Since -2 is left over, the S must = +6.

#6. Group I = +1Group II = +2


Examples

EXAMPLES

H2SO4

H =O =S =

MoO4 -2

Mo = O =

+1

-2

+6

-2

+6


Determining redox species

Determining REDOX Species


4 fe 2 fe 2 1 e

4 Fe  2 Fe2 + 1 e-

Was an electron gained or lost?

An electron was produced or lost by Fe.

LEO .. Losing electrons is oxidation.

Fe was oxidized.


1 e 3 o 2 2 o 3

1 e- + 3 O2 2 O3

Was an electron gained or lost?

An electron was gained by O2.

GER .. Gaining electrons is reduction.

Oxygen was reduced.


Redox reactions

Oxidation and Reduction ALWAYS occur together.

One cannot occur without the other.


How does this occur

How does this occur?

By oxidizing and reducing agents

  • Oxidizing Agent = substance that removes an electron from another species

    • Ex . oxygen

  • Reducing Agent = substance that donates an electron to another species

    • Ex. Iron, metals

Full Rxn:4Fe + 3O2 → 2Fe2O3

Half Rxn: Fe0 → Fe3+ + 3e−

Half Rxn: O2 + 4e− → 2 O2−

Iron is the reducing agent

Oxygen is the oxidizing agent


Full rxn 4fe 3o 2 2fe 2 o 3 half rxn fe 0 fe 3 3e half rxn o 2 4e 2 o 2

Full Rxn:4Fe + 3O2 → 2Fe2O3

Half Rxn: Fe0 → Fe3+ + 3e−

Half Rxn: O2 + 4e− → 2 O2−

  • Iron (Fe) has been oxidized because the oxidation number increased. (0  +3)

  • Iron (Fe) is the reducing agent because it gave electrons to the oxygen (O2).

  • Oxygen (O2) has been reduced because the oxidation number has decreased. (0  -2)

  • Oxygen (O2) is the oxidizing agent because it took electrons from iron (Fe).


Cl 2 g 2nabr aq 2nacl aq br 2 g

O

+1

-1

-1

+1

Cl2 (g) + 2NaBr (aq)  2NaCl (aq) + Br2 (g)

O

1. Assign Oxidation Numbers

2. Is it REDOX? Did oxidation numbers change?

3. LEO goes GER

Who is oxidized?

Who is reduced?

Who is the oxidizing agent?

Who is the reducing agent?

Bromine

Chlorine

Chlorine

Bromine


Example

Example


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