1. Chemistry SM-1232 Week 10 Lesson 3
Dr. Jesse Reich
Assistant Professor of Chemistry
Massachusetts Maritime Academy
Spring 2008

2. Class Today No class Friday Tests are graded
Quizes are not yet graded. I’ll have them sometime this week.
Only 1 wiki even started!!! GET ON IT! At least start the page.
Quote
Chapter 16- just two days, today and Wednesday
Quiz on the Wiki on Friday
Start Chapter 18 on Monday, Test next Wednesday

3. Sea Fever
I must down to the seas again, to the lonely sea and the sky, And all I ask is a tall ship and a star to steer her by, And the wheel's kick and the wind's song and the white sail's shaking, And a grey mist on the sea's face, and a grey dawn breaking. I must down to the seas again, for the call of the running tide Is a wild call and a clear call that may not be denied; And all I ask is a windy day with the white clouds flying, And the flung spray and the blown spume, and the sea-gulls crying. I must down to the seas again, to the vagrant gypsy life, To the gull's way and the whale's way where the wind's like a whetted knife; And all I ask is a merry yarn from a laughing fellow-rover And quiet sleep and a sweet dream when the long trick's over. By John Masefield ( ). (English Poet Laureate, )

4. Oxidation 2 H2 + O2  2H2O 4 Fe(s) + 3O2  2 Fe2O3
CH4 + O2  CO2 + H2O
Each chemical reacting with oxygen ends up with oxygen in the formula. Since they gain oxygen we call it an oxidation or an oxidizing reaction.

5. Reduction 2 H2O  2H2 + O2 2 Fe2O3(s)  4Fe + 3O2
CO2 + H2O  CH4 + 2 O2
The reaction produces oxygen in each case. When the reaction loses oxygen it’s called a reduction.

6. Oxydation does not need oxygen
4 Na + O2  2Na2O
2 Na + Cl2  2 NaCl
Chemists consider both to be oxidation reactions

7. A closer look 4 Na + O2  2Na2O Each Na is losing an electron
4Na  4Na+ + 4e-
Oxygen is gaining two electrons
O2 + 4e- 2O2-

8. similarly 2 Na + Cl2  2 NaCl Each Na is losing an electron
2Na  2Na+ + 2e-
Chlorine is gaining one electrons
Cl2 + 2e- 2Cl-

9. You try
Mg + Cl2  MgCl2
2Ca + O2  CaO

10. Simpler definition LeoGer Aka Leo the Lion goes Ger
Lose electrons = oxidation
Gain Electrons = reduction

11. Redox reactions happen simultaneously
As an oxidation occurs to lose electrons a reduction is happen to gain electrons.
The substance that is oxidized is called the reducing agent because it causes the reduction of the other substance.
The substance that is reduced is called the oxidizing agent because it causes the oxidation of the other substance.

12. Labels Applied
2H2 + O2  2H2O
H2 is the reducing agent because it’s reducing oxygen.
O2 is called the oxidizing agent because it’s oxidizing H2.

13. You try
Write the reactions and label which is the oxidizing agent and which is the reducing agent.
2Mg + O2  MgO
Fe + Cl2  FeCl2
Zn(s) + Fe+2  Zn+2 + Fe(s)

14. Oxydation State: keeping track of electrons
C + 2S  CS2
Let’s figure out where the electrons are!

15. Rules! 1. Pure elements have an oxydation state of 0
2. Any charged ion has an oxydation state equal to its charge
3. If a compound is neutral the sum of all oxydation states equals 0
4. If a compound is charged the sum of all oxydation states equals the charge
5. Group 1,2,3 will always be +1,+2,+3
6. Non metals get oxidation numbers on the next slide.

16. More Rules: Oxidation numbers
This is list is also in order of precedence!
Fluorine oxidation is always -1
Hydrogen is +1
Oxygen is -2
Group 7 is -1
Group 6 is -2
Group 5 is -3

17. Examples
Br2 K+
LiF
CO2
SO42-
Na2O2

18. Back to Carbon and Sulfur
C + 2S  CS2
What are the oxidation states?
What gets oxidized?
What gets reduced?
Which is the oxidizing agent?
Which is the reducing agent?

19. Balancing Redox Equations
Al(s) + Ag+(s)  Al3(aq)+ + Ag(s)
What are the oxidation numbers of each one of these?
Let’s break this down into the oxidation and the reduction!

20. Oxidation Al  Al+3 What’s the oxidation state of Al? Al+3
This isn’t balanced!
We’re missing the electrons!
Al  Al+3 + 3e-
Now we are balanced!

21. Reduction Ag+  Ag(s) What’s the oxidation state of Ag(s)? Ag+?
This isn’t balanced!
We’re missing the electrons!
Ag + + e-  Ag(s)

22. Let’s look at them together
Al(s)  Al+3 + 3e-
1 e- + Ag+  Ag(s)
How many times must Ag+ be reduced in order for 1 Al(s) be oxidized?

23. 3 Times! Al(S)  Al+3 + 3 e- 3(1e- + Ag+  Ag(s)) Al(s)  Al+3 + 3e-
If we add them the electrons can cancel out.
Al(s) + 3 Ag+  3 Ag(s) + Al+3

24. You Try Al(s) + Cu+2  Al+3 + Cu(s)
We’re looking to have charge and atom balanced!

25. Still Time?
I- + Cr2O7-2  Cr3+ + I2(s)

26. Read all of chapter 16 Work on your wikis Work on your homework
Homework due Monday
Take Home Quiz on Friday Too
Review Monday- Start Chapter 18
Quiz on Wednesday.