Oxidation and Reduction Chapter 20

INTRO TO REDOX Day 1

 A reaction in which electrons are transferred from one substance to another  Oxidation cannot occur without reduction  Oxidation: 1.Losing of electrons 2.Increasing the oxidation charge (0 to +1 or -2 to -1)  Reduction 1.Gaining of electrons 2.Reducing the oxidation charge (-1 to -2 or 1 to 0) Definition

 Number of charges the atom would have in a molecule if electrons were transferred completely  Rule #1 Oxidation number of a free element is zero Example: Mg, H 2, Na, P 4, S 8, K  Rule #2 Oxidation number of an ion is the charge of the ion Example: Mg 2+, O 2−, Al 3+, Br − Oxidation Numbers

 Rule #3 Oxidation number for H is +1 when bonded to a nonmetal *Exception: when bonded to a metal it is −1 Example: HCl, HF, LiH, H 2 O, NaH, MgH 2  Rule #4 Oxygen’s oxidation number is −2 *Two Exceptions: peroxides and fluorine Example: H 2 O 2 OF 2

1.HNO 3 2.NO 3 − 3.MgCl 2 4.CO 3 2− 5.NH 3 6.K 3 PO 4 7.CaSO 4 8.SiCl 4 Practice

1.Give the oxidation # of the nitrogen atom: 2.Determine the oxidation # of the sulfur atom 3.Indicate the oxidation # of phosphorus in each: Whiteboard Practice a.N 2 b.NO c.N 2 O 4 d.N 2 O 5 e.NO 2 − f.NH 4 + a.H 2 S b.S c.H 2 SO 4 d.S 2 2− e.HS − f.SO 2 a.HPO 3 b.H 3 PO 2 c.H 3 PO 3 d.H 3 PO 4 e.H 4 P 2 O 7 f.H 5 P 3 O 10 g.SO 2

½ REACTIONS Day 2

 2 Mg + O 2 2 MgO Redox Reaction

 When an electron is lost (electrons appear as products)  X 0 X +1 + e −  Oxidation # goes up Oxidation ½ Reaction  When an electron is gained (electrons appear as reactants)  e − + Y +1 Y 0  Oxidation # goes down Reduction ½ Reaction

LEO goes GER Ways to Remember OIL RIG OSEOSE LECTRONSLECTRONS XIDATIONXIDATION AINAIN LECTRONSLECTRONS EDUCTIONEDUCTION XIDATIONXIDATION S OSINGOSING EDUCTIONEDUCTION SAININGAINING

 Ex1 Na 0  Na +1  Ex2 Fe +3  Fe +2  Ex3 N +1  N +2  Ex4 Mg +2  Mg 0 Examples :

REDOX REACTIONS Day 3

HCl + Zn  ZnCl 2 + H 2 Example 1:

Example 2: Mg + N 2  Mg 3 N 2

Example 3: H 2 S + Cl 2  HCl + S

Example 4: Fe + O 2  Fe 2 O 3

Assign oxidation numbers for each element. Then, for the following balanced redox reactions answer the following questions: 1)Fe(aq) + H 2 O 2 (aq)  Fe +2 (aq) + 2 OH -1 (aq) a.Write all the oxidation numbers (identify what changes) b.Write the ½ reactions on the lines _______________________ ________________________ (oxidation or reduction)(oxidation or reduction) c.Add the electrons to each ½ reaction d.Identify each ½ reaction as oxidation or reduction Classwork

2) Zn(s) + HCl(aq)  H 2 (g) + ZnCl 2 (aq)

3) SbCl KI  SbCl 3 + I KCl