Bellwork- Redox

Which species is oxidized? Which one is reduced? What acts as the oxidizing agent?

H+ (aq) + Li(s) Li+(aq) + H2(g)

N2(g) + O2(g) 2NO2(g)

Bellwork- Redox

Which species is oxidized? Which one is reduced? What acts as the oxidizing agent?

H+ (aq) + Li(s) Li+(aq) + H2(g)

C(s) + O2(g) 2CO2(g)

Cations in compounds or solutions are reduced to elemental metals

ex. Na+ + e- Na(s) reduction half-reaction

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Metals are oxidized into cationsex. Al(s) Al3+ + 3e- oxidation half-reaction

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Combustion reactions are redox reactions.

Ex. CH3 + O2 CO2 + H2O

Carbon & hydrogen are oxidized.

Oxygen is reduced.

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The attachment of oxygen is oxidation.

Ex. C becomes part of CO2

Carbon is oxidized.

Oxygen is always reduced.

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Assign an oxidation number to each

atom using the rules:

1. Elements are 0. ex. O2(g) , H2(g), Li(s)

Monatomic ions are their charge. ex. Na+ is +1 and Cl- is -1

2. For compounds

Oxygen is -2 Hydrogen is +1

The sum of the oxidation numbers must equal the charge on the compound.

Ex.

CO2

Oxygen is -2 and there are two, so carbon is +4.

2(-2) + _____ = 0+4

Ex.

NO3-

O is -2.

3(-2) = -6

-6 + _____ = -1-5

An increase in oxidation number is oxidation

A reduction in oxidation number is reduction

An element has been oxidized if..

• Electrons are lost

• Oxidation number increases

• Oxygen is gained Ex. S SO2

• Hydrogen is lost C2H6 C2H4