Oxidation & Reduction

Oxidation & Reduction

Definition of Redox Reaction

} Oxidation Reduction Reaction (Redox):

A reaction in which electrons are ______from one substance to another.

Definition of Redox Reaction

} Oxidation cannot occur without ______

} Definition of Oxidized:

1. Losing of ______(LEO)

2. Increasing the oxidation charge, ie: 0 to +1

-2 to -1

3. Gaining ______

} Definition of Reduced:

1. ______of electrons (GER)

2. Reducing the oxidation charge, ie: -1 to -2

1 to 0

3. Losing ______

Example of an electron transfer reaction

} 2Mg + O2 à 2MgO

} Mg atom ______two electrons to each oxygen atom.

} As a result 2 Mg atoms become Mg2+ and two oxygen atoms become ______

} Mg ______two electrons

} O ______two electrons

Examples of Oxidation Reduction

} When an electron is ______ (An electron is found on the product side) there is ______

◦ X0 à X+1 + e-

} When an electron is ______ (An electron is found on the reactant side) there is ______

◦ e- +Y+1 à Y0

Examples:

start finish Oxidation or Reduction

} Ex5 Na0 à Na+1 ______

} Ex6 Fe+3 à Fe+2 ______

} Ex7 N+1 à N+2 ______

} Ex8 Mg+2 à Mg0 ______

Vocabulary

} Whatever is ______is called the reducing agent

} Whatever is ______is called the oxidizing agent

} Real Examples:

start finish Oxidizing agent or reducing agent

} Ex5 Na0 à Na+1 ______

} Ex6 Fe+3 à Fe+2 ______

} Ex7 N+1 à N+2 ______

} Ex8 Mg+2 à Mg0 ______

Redox Homework #1:

What is a redox reaction?

Can oxidation occur without reduction? Explain.

Define oxidation and reduction in terms of the gain or loss of oxygen.

Define oxidation and reduction in terms of the gain or loss of electrons.

How is a change in oxidation number related to the process of oxidation and reduction?

Half-Reactions for Oxidation/Reduction

A half-reaction is an equation just showing just the oxidation or just the reduction reaction that takes place in a redox reaction.

State whether the half-reaction is oxidation or reduction.

K+ +e- à K ______
Ca à Ca2+ + 2e- ______
2Br - à Br2 + 2e- ______
S + 2e à S2- ______
F2 + 2e- à 2F- ______

Write where the electron(s) is lost or gained. Then determine if each equation is oxidation or reduction.

Na à Na+ ______
Mg2+ à Mg ______
K à K+ ______
Fe2+ à Fe3+ ______
Ag+ à Ag ______
I 2 à 2I- ______
Zn2+ à Zn ______
2F- à F2 ______
Al3+ à Al ______
Cl2 à 2Cl- ______

Redox Rules:

Redox Rules to Learn for Ionic and Covalent Bonds

Electronegativity and Redox Rules

} Definition: Electronegativity is the atom’s ability to ______electrons.

} ______is the most electronegative element

Electronegativity Trend

Rule #1

Oxidation number of an ______atom = zero (no compounds or ions)

i.e . Mg, H2, Na

ie. All H2 O2 N2 Cl2 Br2 I2 F2 ’s ox. # are zero

Rule #2

Oxidation number of a ______ion = charge of the ion

i.e. Mg2+ , O2- , Al3+ , Br –

Rule #3

The sum of the oxidation numbers of a ______compound = 0

i.e. H2O CO2 CO NaCl

Rule #4

The oxidation number for H is ______

Exception: when bonded to a ______electronegative element (metal), then it is ______.

i.e. LiH NaH MgH2

i.e. HF Cl

Rule#5

Oxygen’s oxidation number is ______, in a compound

Two exceptions: peroxides and fluorine

in H2O2 where O is ______

with OF2 where O is ______

Rule#6

Oxidation number of

polyatomic ______= 0 (same as rule #3)

polyatomic ______= the charge of the ion

i.e. compounds:

NH3 SiCl4 K3PO4

i.e. ions:

NH4+ CO32- SO42- NO3-

Rule#7

Oxidation numbers for ______in:

Group 1A metal compound +1

2A metal compound +2

3A Aluminum compound+ +3

i.e. NaCl MgSO4 AlPO4

Rule#8

The most electronegative element ______ALWAYS has an oxidation number of -1 when it is bonded to another element. i.e. HF

Question Time

Assign oxidation numbers to each element

1. Cl2 2. Cl- 3. MgCl2 4. NaH

5. HCl 6. K3PO4 7. CaSO4 8. KF

Classwork: Redox Rules

1. Give the oxidation numbers of all the elements in the following molecules and ions:

a. N2O b. NO c. N2O4 d. N2O5 e. NO2- f. NO3-

2. Determine the oxidation number of the sulfur atom:

a. H2S b. S c. H2SO4 d. S2- e. HS- f. SO2 g. SO3

3. Indicate the oxidation number of phosphorus in each of the following compounds:

a. HPO3 b. H3PO2 c. H3PO3 d. H3PO4 e. H4P2O7 f. H5P3O10

Redox Homework #2: Oxidation Numbers and Rules Worksheet

The oxidation number of an atom is the apparent charge assigned to it in a particular molecule, ion or compound. Certain rules are followed in assigning oxidation numbers. Use rules at the right to assign oxidation numbers to each element in each of the given formulas.

Example

OXIDATION NUMBER

H2O H=+1, O= −2

N2 N=0

OXIDATION NUMBER

1. Cl2 ______

2. Cl− ______

3. Na ______

4. Na+ ______

5. KCl ______

6. H2S ______

7. CaO ______

8. H2SO4 ______

9. NO3− ______

10. Cr2O72- ______

11. NH4Cl ______

12. NH3 ______

13. NO2 ______

14. CaH2 (calcium hydride) ______

15. Na2O2 (sodium peroxide) ______

Cw: Give oxidation numbers for the underlined atoms in these molecules and ions:

a. Cs2O

b. PtCl62-

c. CaI2

d. SnF2

e. Al2O3

f. ClF3

g. H3AsO3

h. SbF6-

i. TiO2

j. P4

k. MoO42-

l. MnO4-

m. PtCl42-

n. O2

o. O3

Redox Homework #3: Oxidation Numbers Worksheet

Directions: Use the Rules for Assigning Oxidation Numbers to determine the oxidation number assigned to each element in each of the given chemical formulas.

Formula / Element and Oxidation Number / Formula / Element and Oxidation Number
1. / Cl2 / Cl / 16. / Na2O2 / Na / O
2. / Cl- / Cl / 17. / SiO2 / Si / O
3. / Na / Na / 18. / CaCl2 / Ca / Cl
4. / Na+ / Na / 19. / PO43- / P / O
5. / O2 / O / 20. / MnO2 / Mn / O
6. / N2 / N / 21. / FeO / Fe / O
7. / Al+3 / Al / 22. / Fe2O3 / Fe / O
8. / H2O / H / O / 23. / H2O2 / H / O
9. / NO3- / N / O / 24. / CaO / Ca / O
10. / NO2 / N / O / 25. / H2S / H / S
11. / Cr2O72- / Cr / O / 26. / H2SO4 / H / S / O
12. / KCl / K / Cl / 27. / NH4Cl / N / H / Cl
13. / NH3 / N / H / 28. / K3PO4 / K / P / O
14. / CaH2 / Ca / H / 29. / HNO3 / H / N / O
15. / SO42- / S / O / 30. / KNO2 / K / N / O

NT: Using the Rules (Last Lesson of the Year!)

Oxidation Number

} If oxidation number goes ______it is ______.

Using the Rules

Balance the reactions, write the oxidation numbers for each atom and write the oxidizing and reducing agents.

Ex1 HCl + Zn à ZnCl2 + H2

Ex2 Mg + N2 à Mg3N2

Ex3 H2S + Cl2 à HCl + S

Ex4 Fe + O2 à Fe2O3

Summary of Oxidation/Reduction

There are three definitions of oxidation and reduction:

Oxidation Reduction

1.______1.______

2.______2.______

3.______3.______

Two ways to remember oxidation/reduction is:

L E O goes G E R or O I L R I G

Classwork: Using Rules to Balance Equations

Assign oxidation numbers for each element. Then, for the following balanced redox reactions answer the following questions:

1) Fe(aq) + H2O2(aq) à Fe+2(aq) + 2 OH-1(aq)

a. What is the oxidation state of oxygen in H2O2?

b. What is the element that is oxidized?

c. What is the element that is reduced?

d. What is the oxidizing agent?

e. What is the reducing agent?

f. How many electrons are transferred in the reaction as it is balanced?

2) 4NaOH(aq) + Ca(OH)2(aq) + C(s) + 4ClO2(g) à 4NaClO2(aq) + CaCO3(s) + 3H2O(l)

a. What is the oxidation state of Cl in ClO2(g)?

b. What is the oxidation state of C in C(s)?

c. What is the element that is oxidized?

d. What is the element that is reduced?

e. What is the oxidizing agent?

f. What is the reducing agent?

g. How many electrons are transferred in the reaction as it is balanced?

3) 16 HCl(aq) + 5 SnCl2(aq) + 2 KMnO4(aq) à 2 MnCl2(aq) 5 SnCl4(aq) + 8 H2O(l) + 2 KCl(aq)

a. What is the oxidation state of Mn in KMnO4(aq)?

b. What is the oxidation state of Sn in SnCl2(aq)?

c. What is the element that is oxidized?

d. What is the element that is reduced?

e. What is the oxidizing agent?

f. What is the reducing agent?

g. How many electrons are transferred in the reaction as it is balanced?

Redox Homework #4: Using Rules to Balance Equations

Balance each equation. Assign oxidation numbers to each atom. Determine what is oxidized/reducing agent and what is reduced/oxidizing agent. Tell the number of electrons transferred.

1. Na + Cl2 à NaCl Oxidized (Reducing Agent)______

Reduced (Oxidizing Agent) ______