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Redox Reactions. Chapter 18. + O 2 . Oxidation-Reduction (Redox) Reactions. “redox” reactions: rxns in which electrons are transferred from one species to another oxidation & reduction always occur simultaneously we use OXIDATION NUMBERS to keep track of electron transfers.

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Redox reactions

Redox Reactions

Chapter 18

+ O2


Oxidation reduction redox reactions
Oxidation-Reduction (Redox) Reactions

  • “redox” reactions: rxns in which electrons are transferred from one species to another

  • oxidation & reduction always occur simultaneously

  • we use OXIDATION NUMBERS to keep track of electron transfers


Rules for assigning oxidation numbers
Rules for Assigning Oxidation Numbers:

1) the ox. state of any free (uncombined) element is zero.

  • Ex: Na, S, O2, H2, Cl2, O3


Rules for assigning oxidation numbers1
Rules for Assigning Oxidation Numbers:

2) The ox. state of an element in a simple ion is the charge of the ion.

Mg2+ oxidation of Mg is +2


Rules for assigning oxidation numbers2
Rules for Assigning Oxidation Numbers:

  • 3) the ox. # for hydrogen is +1

    (unless combined with a metal, then it has an ox. # of –1)

    Ex: NaOH (H bonded to O) v. NaH (H bonded to Na)


Rules for assigning oxidation numbers3
Rules for Assigning Oxidation Numbers:

4) the ox. # of fluorine is always –1.


Rules for assigning oxidation numbers4
Rules for Assigning Oxidation Numbers:

5) the ox. # of oxygen is usually –2.

Why USUALLY? Not -2 when it’s in a peroxide, such as hydrogen peroxide:

H2O2


Rules for assigning oxidation numbers5
Rules for Assigning Oxidation Numbers:

6) in any neutral compound, the sum of the oxidation #’s = zero.


Rules for assigning oxidation numbers6
Rules for Assigning Oxidation Numbers:

7) in a polyatomic ion, the sum of the oxidation #’s = the overall charge of the ion.


Rules for assigning oxidation numbers7
Rules for Assigning Oxidation Numbers:

**use these rules to assign oxidation #’s; assign known #’s first, then fill in the #’s for the remaining elements:


Examples assign oxidation s to each element
Examples: Assign oxidation #’s to each element:

a) NaNO3


Examples assign oxidation s to each element1
Examples: Assign oxidation #’s to each element:

b) SO32-


Examples assign oxidation s to each element2
Examples: Assign oxidation #’s to each element:

c) HCO3-


Examples assign oxidation s to each element3
Examples: Assign oxidation #’s to each element:

d) H3PO4


Examples assign oxidation s to each element4
Examples: Assign oxidation #’s to each element:

e) Cr2O72-


Examples assign oxidation s to each element5
Examples: Assign oxidation #’s to each element:

f) K2Sn(OH)6


Definitions
Definitions

  • Oxidation: the process of losing electrons (ox # increases)

  • Reduction: the process of gaining electrons (ox # decreases)

  • Oxidizing agents: species that cause oxidation (they are reduced)

  • Reducing agents: species that cause reduction (they are oxidized)


To help you remember
To help you remember…

OIL RIG

  • Oxidation Is Loss

  • Reduction Is Gain


Are all rxns redox rxns
Are all rxns REDOX rxns?

  • a reaction is “redox” if a change in oxidation # happens; if no change in oxidation # occurs, the reaction is nonredox.


Examples
Examples

MgCO3 MgO + CO2


Examples1
Examples

Zn + CuSO4 ZnSO4 + Cu


Examples2
Examples

NaCl + AgNO3 AgCl + NaNO3


Examples3
Examples

CO2 + H2O  C6H12O6 + O2


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