Oxidation and Reduction Reactions

Theme: Stability and Change

Examples:

• Rusting, Tarnish• Spoiling, Aging• Electrochemistry and batteries

Definitions

• Oxidation: Loss of electrons by a substance.• Reduction: Gain of electrons by a substance.

• In the next animation, see if you can tell which metal is being oxidized and which is being reduced?

How does the redox reaction run the battery?

• http://content.blackgold.ca/ict/Division4/Science/Div.%204/Voltaic%20Cells/demo.htm

Can “antioxidants” prevent aging?

• Oxygen and other “free radicals” can cause the oxidation of molecules that make the body’s tissues.

• Can we prevent this?– Ex. Vitamin C is an antioxidant. Oxidation causes

the browning of cut apples. By adding lemon juice (Vit C) to cut apples, we prevent oxidation!

Writing a “redox” reaction

Balanced equation for the whole reaction:• Zn + 2HCl ZnCl2 + H2

• Since it is on both sides as a Cl-, chlorine is a spectator ion!

Half reaction showing the oxidation of zinc:• Zn0 Zn 2+ + 2e-Half reaction showing the reduction of hydrogen:• 2H+ + 2 e- H2

Why does zinc “replace” hydrogen?

• Think: stability and change

• Why might it be important to know the reactivity of metals?

Virtual Lab

• Lab Goals:– To determine the reactivity series of a set of

metals using experimental data.– To observe and balance redox reactions.

Followup check:

• Magnesium metal and aluminum chloride combine to form magnesium chloride and aluminum metal. The whole reaction is:– 3 Mg + 2 AlCl3 3 MgCl2 + 2 Al

Write the half reaction for oxidation and the half reaction for reduction.

This reaction only works one way. Aluminum cannot displace magnesium. What does this say about the stability of aluminum vs. the stability of magnesium?