Big Idea 14
Redox and Electrochemistry
Chemistry - The Central Science Textbook
https://sites.lps.org/sputnam/LHS_IB/IBChemistry/Chemistry_Brown_12th.pdf
The chapter for this unit is Chapter 20.
Oxidation Numbers
In Chemistry 11, we learned charge or "oxidation" numbers show the gain or loss of electrons in an ion. This is partially true.
Positive oxidation numbers show loss of electrons resulting in a net positive charge. For ionic compounds, this is a true loss of electrons. For covalent compounds where electrons are shared as opposed to lost, this charge is just assumed.
Negative oxidation numbers show gain of electrons resulting in a net negative charge. For ionic compounds, this is a true gain of electrons. For covalent compounds where electrons are shared as opposed to gained, this charge is just assumed.
REDOX Reactions
There is a whole vernacular that goes along with "REDOX" reactions - chemical reactions where electrons are gained and lost. The graphic to the right is an excellent summary of this wording.
OIL RIG
Oxidation Number and OIL RIG Practice
Oxidation Number and Redox Practice.pdf
Half Reactions with Electrons
REDOX reactions are typically split into two "half reactions". One of these reactions is gaining electrons (the negative half), while the other reactions is losing electrons (the positive half).
Half Reaction Examples and Practice
These are the half reaction examples and practice used in class.
Half Reaction Examples.pdfHalf-Reaction Practice.pdfIntro Lab - REDOX Half Reactions With Metals and Metal Solutions
This intro lab allows students to work with simple metal-metal solution REDOX reactions while gaining experience in determining half-reactions
Intro Lab Data Chart.pdfBalancing REDOX Reactions in Acidic and Basic Solutions
One of the more complex sequential processes in Chemistry 12 is balancing REDOX reactions for both mass and charge. This process can be done in either acidic or basic environments. The sequential portion of the balancing is NOT well-explained in most college chemistry courses, so we attempt to cover it slowly and in-depth in this course.
Balancing Acidic Reactions
Both the in-class example and practice reactions are on this document. The practice reaction answers are given, but not worked out. Please ask Mr. Dralle for assistance if you need it!
Balancing Acidic Rxn.pdfBalancing Acidic Rxn Notes.pdfBalancing Basic Reactions
Both the in-class example and practice reactions are on this document. The practice reaction answers are given, but not worked out. Please ask Mr. Dralle for assistance if you need it!
Balancing Basic Rxn.pdfBalancing Basic Rxn Notes.pdfBalancing Reaction Practice Equation Answers
Acidic Reaction Balance Answers.pdfBasic Balance Reaction Answers.pdfRedPot Chart.pdfStandard Reduction Potential Tables
A common reference document used in electrochemistry is the Standard Reduction Potential or "Red Pot" table. This tables shows the typical electron exchange associated with various reduction half reactions. This electron exchange is then translated to a voltage potential.
Keep in mind - everything on this table is REDUCTION. There are also standard OXIDATION tables available.
RedPot Chart Notes.pdfGalvanic Cells
Galvanic cells harness the movement of electrons in REDOX reactions to create an electrical potential (voltage). This voltage acts like a force that can move a flow of electrical charge. A common Zn-Cu galvanic cell is show to the right. The class notes for this reaction are shown below.
Galvanic Reaction Example.pdf
Galvanic (Electrochemical) vs Electrolytic Cells
The difference between electrochemical and electrolytic cells often shows up in college chemistry textbooks. Basically, they are the reverse of each other. Notice the two-way arrows in the reactions shown below.
Galvanic Reaction Full Lab
The purpose of this lab is to investigate the voltage potential associated with various galvanic combinations of metals.
Questions:
"How does the galvanic potential of metal combinations measured in lab vary from the potential predicted by standard reduction tables?"
"What effect does varying the electrolyte have on electrical potential?"
If-Then-Due-To Hypothesis: "If two metals and an electrolyte are placed together, then an electrical potential should be able to be measured due to the exchange of electrons between the metals."
Variables: (x1) metal combination, (x2) electrolyte; (y) electrical potential (V)
Constants: the same metal combinations are tested in all three electrolyte solutions
Control: the voltage potentials as predicted by the standard reduction potential table
Galvanic Corrosion
An unfortunate part of electrochemistry and galvanic cells is "galvanic corrosion". This type of corrosion occurs when two dissimilar metals come in contact with an electrolyte, and a path for electron flow is established.
Skeptical Questions In Science
The skeptical question topic for this unit involves how powerful a small battery can be. Skeptical questions are thoughtful "Why-based" questions which address biases in scientific material. This type of question is not seeking scientific facts.
The articles associated with this unit are listed below:
Learning-2-Learn and Retrieval Assignments (Required before taking the Unit Graded Test!) and Calibration Test
Copper Sulfate Reactions Intro Lab Data and Reflection
Practice (Half-Reaction Problems, Balancing Acidic and Basic Reactions Practice)
Calibration Practice Test