10.1: Oxidization and Reduction Objectives S1

Essential Questions What is oxidation? Reduction? How do you assign oxidation numbers? What is a half reaction? How do you write half reactions?

Oxidation and Reduction Reactions Oxidation-Reduction reactions (redox) is when electrons are being gained and lost during a chemical reaction Originally oxidation was defined as gain of oxygen while reduction was loss of oxygen

Oxidation and Reduction Reactions (cont) Definitions using oxygen were limited in scope so following definition are now used: Oxidation is loss of electrons Reduction is gain of electrons OIL RIG

Oxidation and Reduction Reactions (cont) When magnesium and sulfur are heated together, they undergo an oxidation-reduction reaction to form magnesium sulfide. Applying Concepts Where did the electrons lost by magnesium go?

Oxidation Numbers Oxidization numbers are how we keep track of what is happening to electrons Similar to charge but not exactly the same There are set rules when determining oxidation numbers

Oxidation # Rules Oxidation numbers are written per atom Oxidation number of neutral element by itself is Zero For most elements the oxidation # correlates with the charge of atom For metals it will equal the metal’s charge H is +1 when bonded to nonmetals and -1 when bonded to metals Cl, Br, and I are -1 except when bonded to F and O O is usually -2 unless bonded to F F is always -1

Oxidation # Rules Sum of oxidation # for all atoms in a compound is equal to 0 Sum of oxidation # equal the charge of the ion. Figure out what you know and use the sum to find the rest.

Assigning Oxidation Numbers Find the oxidation number for each element Na CaO N3- SrCl2 NO3- CoO Cu(NO3)2 K2Cr2O7 Cs2(SO4)3

Half Reactions Oxidation never occurs without reduction, they always occur in pairs The total formula can be written in two parts The oxidation half (where the oxidation number has increased) The reduction half (where the oxidation number has decreased/reduced)

Writing Half Reactions Cu + 2 AgNO3 → Cu(NO3)2 + 2 Ag Step 1: Determine Oxidation numbers for each atom on each side of the equation Step two: determine which two atoms have changed oxidation #s Step three: Write half reactions for those two elements Step four: Add electrons to balance charges or oxidation # Recall: Oxidation is losing electrons and reduction is gaining electrons

Balancing Half-Reactions (cont) Write balanced half reactions and identify the elements reduced and oxidized for the following: TiO2 + 2 Mg → Ti + 2 MgO Cl2 + 2 NaBr → 2 NaCl + Br2 5 CO + I2O5 → I2 + 5 CO2

Essential Questions What is oxidation? Reduction? How do you assign oxidation numbers? What is a half reaction? How do you write half reactions?

10.1 Tracked Assignment worksheet