Oxidation – Reduction Mr. Chan Northwestern University To insert your company logo on this slid From the Insert Menu Select “Picture” Locate your logo file Click OK To resize the logo Click anywhere inside the logo. The boxes that appear outside the logo are known as “resize handles.” Use these to resize the object. If you hold down the shift key before using the resize handles, you will maintain the proportions of the object you wish to resize.

Defining Redox Oxidation - reduction  Originally combining with oxygen  Reduction – originally meant loss of oxygen Oxidation – loss of electrons Reduction – gain of electrons  OILRIG Oxidizing and Reducing Agents  Red. Agent – loses electrons, gets oxidized  Ox. Agent – gains electrons, gets reduced Practice 1-2 Corrosion – some metals corrode faster than others

Determining Oxidation Numbers Oxidation number – pos. or neg. number assigned to an atom Metals - often just the ionic charges Other elements – what ionic charge it would have if it were a metal

Rules of Assigning Oxidation Numbers 1) Monatomic ions = charge 2) Hydrogen = +1 (except hydride) 3) Oxygen = -2 (peroxide O 2 2- ) 4) Pure element = 0 5) Neutral compound – sum of ox. Numbers = 0 6) Polyatomic ion – sum of ox. Numbers = ionic charge of ion Practice 9-10

Changes in Oxidation Numbers Redox reaction  Oxidized – increase in ox.number  Reduced – decrease in ox. Number Practice 11

Identifying Redox Reactions Look at oxidation numbers Look for changes in Ox. Numbers Identify Ox. Substance, Red. Substance, Ox./Red. Agents

Balancing Redox Reactions Multiplying oxidation numbers Use least common multiples and balance Practice 19-20

Using Half Reactions Method Write unbalanced equation in ionic form Write separate half-reactions Balance atoms in half reactions  Balance Oxygens by adding water  Balance Hydrogens by adding hydrogen ions Add electrons – balance charges Multiply each reaction – make total numbers of electrons equal Add half reactions Add spectator ions Practice 21-22