OXIDATION AND REDUCTION

Oxidation • Losing electrons• The higher positive oxidation number the more the atom

has loss control over the electrons, therefore the more oxidized it is.

Reduction • Gaining electrons• The higher negative oxidation number the more it has

gain electron control, therefore the more reduced it is.

Redox• Redox reaction is a chemical reaction in which changes in

the oxidation numbers occur• Oxidation and reduction always occur together

Oxidation Number• Oxidation number is a measure of the electron control that

the atom has

Redox or Not?

• 2H2 + O2 2H2O

• Mg + O2 MgO

• CH4 + O2 CO2 + H2O

• Pb(NO3)2 + 2KI PbI2 + 2KNO3

• Na2CO3 Na2O + CO2

• NaOH + KNO3 NaNO3 + KOH

Half-Equation

2Mg(s) + O2(g) 2MgO(s)

2Mg(s) 2Mg2+(s) + 4e-

O2(g) + 4e- 2O2-(s)

This redox reaction is broken down into half-equations to show the electron transfer. Magnesium loses two electrons, which means it becomes oxidized. Oxygen gains two electrons, which means it becomes reduced.

Half-Equation3Mg(s) + N2(g) Mg3N2(s)

3Mg(s) 3Mg2+(s) + 6e-

N2(g) + 6e- 2N3-(s)

This redox reaction magnesium, shown in the half-equation, losing six electrons, therefore being oxidized. Nitrogen is gaining six electrons, therefore being reduced.

Oxidizing Agent• Oxidizing agent is the reactant that accepts electrons

Reducing Agent• Reducing agent is the reactant that supplies the electrons

Oxidation Number• Number with plus or minus defining the relative charge• Predict number• H2S, S, SCl2, SO2, SO3

-2, SO3, H2SO4, Mg, O2, I2

Name using oxidation state• FeO = Iron (II) oxide• Fe2O3 = Iron (III) oxide

• Cu2O = Copper (I) oxide

• CuO = Copper (II) oxide• MnO2 = Manganese (IV) oxide

• K2Cr2O7 = Potassium dichromate (VI)

Reactivity

Reducing Agent Oxidizing Agent

Mg Strongest F2

Al Cl2Zn Br2 = O2

Fe I2

Pb

Cu

Ag Weakest

Who’s more likely to occur?• ZnCl + 2Ag 2AgCl + Zn• 2FeCl3 + 3Mg 3MgCl2 + 2Fe

• 2KI + Cl2 2KCl + I2

• 3Mg + N2 Mg3N2

• 2Mg + O2 2MgO

Voltaic Cell aka Galvanic Cell• Voltaic cell is an electrochemical cell that produces

electrical energy from redox reactions taking place within the cell.

• To generate a current each cell or electrode must have a different electric potential

• The electrode where oxidation occurs is called the anode• The electrode where reduction occurs is called the

cathode• To complete the circuit the metal plates are connected

with a wire and solutions are connected with a salt bridge

Voltaic Cell• Salt bridge completes the circuit• Zn Zn+e-

• Standard Conditions: 298K, 1 atm, 1mol dm-3

• Cell Potential is 1.10V = 0.34 – (- 0.76)• Cu ions are converted to cupper metal on the electrode• If the Zn rod was place in the Cu solution there will be a

color change and heat released