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

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

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 (1878-1967). (English Poet Laureate, 1930-1967.)

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.

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.

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

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

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

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

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

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.

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.

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)

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

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.

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

Examples Br2 K+ LiF CO2 SO42- Na2O2

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?

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!

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!

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)

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?

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

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

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

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.