Lecture 5 Reduction-Oxidation Reactions Redox Reduction-Oxidation Reactions Redox

What is a redox reaction?  ==> When in the reaction, electrons are being transferred from one substance to another.  What has to happen? Something has to be gaining e - (becoming negative) and something has to be losing e - (becoming positive).  ==> When in the reaction, electrons are being transferred from one substance to another.  What has to happen? Something has to be gaining e - (becoming negative) and something has to be losing e - (becoming positive).

How do you tell? Need to assign each individual element an oxidation number.  Rules: 1) When atoms are by themselves (including diatomics) they have an oxidation # of 0. Ex: Na, N 2, Cl 2, O 2, Fe, Mg  Rules: 1) When atoms are by themselves (including diatomics) they have an oxidation # of 0. Ex: Na, N 2, Cl 2, O 2, Fe, Mg

How do you tell? Need to assign each individual element an oxidation number.  Rules: 1)When atoms are by themselves (including diatomics) they have an oxidation # of 0. 2)Monatomic ions have an oxidation # equaling their charge. Ex: Cl -1, Na +1, N -3, O -2, Fe +3, Mg +2  Rules: 1)When atoms are by themselves (including diatomics) they have an oxidation # of 0. 2)Monatomic ions have an oxidation # equaling their charge. Ex: Cl -1, Na +1, N -3, O -2, Fe +3, Mg +2

How do you tell? Need to assign each individual element an oxidation number.  Rules: 1)When atoms are by themselves (including diatomics) they have an oxidation # of 0. 2)Monatomic ions have an oxidation # equaling their charge. 3)Compounds are neutral. Sum of oxidation # must be 0  Rules: 1)When atoms are by themselves (including diatomics) they have an oxidation # of 0. 2)Monatomic ions have an oxidation # equaling their charge. 3)Compounds are neutral. Sum of oxidation # must be 0

How do you tell? Need to assign each individual element an oxidation number.  Rules: 1)When atoms are by themselves (including diatomics) they have an oxidation # of 0. 2)Monatomic ions have an oxidation # equaling their charge. 3)Compounds are neutral. Sum of oxidation # must be 0 4) Polyatomic ions must have the sum of oxidation # equal their charge.  Rules: 1)When atoms are by themselves (including diatomics) they have an oxidation # of 0. 2)Monatomic ions have an oxidation # equaling their charge. 3)Compounds are neutral. Sum of oxidation # must be 0 4) Polyatomic ions must have the sum of oxidation # equal their charge.

How do you tell? Need to assign each individual element an oxidation number.  Rules: 5) Oxygen in a compound usually has a charge of -2. Exception: peroxide where it equals -1  Rules: 5) Oxygen in a compound usually has a charge of -2. Exception: peroxide where it equals -1

How do you tell? Need to assign each individual element an oxidation number.  Rules: 5) Oxygen in a compound usually has a charge of -2. Exception: peroxide where it equals -1 6) In covalent compounds, hydrogen is +1.  Rules: 5) Oxygen in a compound usually has a charge of -2. Exception: peroxide where it equals -1 6) In covalent compounds, hydrogen is +1.

How do you tell? Need to assign each individual element an oxidation number.  Rules: 5) Oxygen in a compound usually has a charge of -2. Exception: peroxide where it equals -1 6) In covalent compounds, hydrogen is +1. Application: NO 2 NO NO 3 l- HC 2 H 3 O 2 SO 4 -2  Rules: 5) Oxygen in a compound usually has a charge of -2. Exception: peroxide where it equals -1 6) In covalent compounds, hydrogen is +1. Application: NO 2 NO NO 3 l- HC 2 H 3 O 2 SO 4 -2

How do you tell? Need to assign each individual element an oxidation number.  Rules: 5) Oxygen in a compound usually has a charge of -2. Exception: peroxide where it equals -1 6) In covalent compounds, hydrogen is +1. 7) If else fails use the periodic table. Group 1 = 1+ Group 2 = 2+ Group 7 = 1-  Rules: 5) Oxygen in a compound usually has a charge of -2. Exception: peroxide where it equals -1 6) In covalent compounds, hydrogen is +1. 7) If else fails use the periodic table. Group 1 = 1+ Group 2 = 2+ Group 7 = 1-

More Practice  Try these brain busters!  KMnO 4  H 2 CO 3  PH 3  MgC 4 H 4 O 6  Try these brain busters!  KMnO 4  H 2 CO 3  PH 3  MgC 4 H 4 O 6

Remember!  Oxidation can be all sorts of numbers, even fractions :] Fe Oxygen is -2, so what does Fe have to be?  Oxidation can be all sorts of numbers, even fractions :] Fe Oxygen is -2, so what does Fe have to be?

Remember!  Oxidation can be all sorts of numbers even fractions :] Fe Oxygen is -2 so what does Fe have to be? Iron is + 8/3  Oxidation can be all sorts of numbers even fractions :] Fe Oxygen is -2 so what does Fe have to be? Iron is + 8/3

Characteristics of Redox reactions:  1) Oxidation-substance losing electrons

Characteristics of Redox reactions:  1) Oxidation-substance losing electrons  2) Reduction-substance gaining electrons  1) Oxidation-substance losing electrons  2) Reduction-substance gaining electrons

Characteristics of Redox reactions:  1) Oxidation-substance losing electrons  2) Reduction-substance gaining electrons  1) Oxidation-substance losing electrons  2) Reduction-substance gaining electrons

Lots of Ways to Remember!  Oil Rig O I L R I G  Oil Rig O I L R I G

Lots of Ways to Remember!  Leo goes Ger L E O goes G E R  Leo goes Ger L E O goes G E R

Lots of Ways to Remember!  Olé! O L E !  Olé! O L E !

2 Na(s) + Cl 2 (g) ==> 2NaCl(s)  What’s being oxidized? Reduced?

Na(s) + Cl 2 (g) ==> 2NaCl(s)  What’s being oxidized? Reduced? Oxidized: Na Reduced: Cl 2  What’s being oxidized? Reduced? Oxidized: Na Reduced: Cl 2