Oxidation and Reduction
Oxidation: the process by which a substance ______
Reduction: the process by which a substance ______
LEO the lion says GER: Lose Electrons, Oxidation; Gain Electrons, Reduction
Redox reactions: Chemical reactions in which electrons are ______between reactants.
Oxidation numbers: A bookkeeping tool - keeps track of ______in redox rxns.
Rules for determining oxidation numbers for elements and compounds:
1. The oxidation number of an atom in an uncombined element is always ______.
2. The oxidation number of any ion equals its ______
3. In compounds, the oxidation number of many elements corresponds to the elements position in the periodic table: a. alkali metals are always ______
b. alkaline earth metals are always ______
c. Aluminum is ______
d. Halogens are almost always ______unless with an oxianion
e. H has an oxidation # of ______when combined with nonmetals
f. Oxygen is always ______
4. The oxidation numbers of elements in compounds are written per atom
5. The ______of the oxidation numbers of all atoms in a compound must equal ______.
6. The sum of the oxidation numbers of all atoms in a polyatomic ion must equal the charge of the ion.
Oxidizing agent: substance that gets ______ by ______electrons from another substance.
Reducing agent: substance that gets ______, because it ______electrons.
So a strong oxidizing agent should have a great tendency to ______e-
A strong reducing agent should be willing to ______e- easily.
Types of Redox Reactions:
1. Combination and Decomposition Reactions: These reactions always go from “0” oxidation states to compounds with different oxidation states, or compounds with oxidations states to elements that are “0”.
2. Single replacement Reactions: Always goes from an element with a “0” to an ion with a “charge” oxidation state or the reverse. Some elements oxidize more readily than others. This is the basis for the activities series of the metals. Also includes the nonmetals ability to be reduced.
3. Combustion Reactions: These reactions involve large amounts of electrons being transferred
Balancing Redox Reactions: The fundamental principle involves electron transfer. The ______of ______MUST be the same in the reduction process and the oxidation process.
Balancing Redox Reactions in Acidic Solution:
1. assign oxidation numbers for all atoms.
2. Identify the element that is oxidized and the element reduced. (LEO says GER). Split the reaction into half-reactions (reduction, oxidation)
3. Balance all elements except hydrogen and oxygen.
4. Balance oxygen atoms by adding H2O. Balance the hydrogen atoms on the other side by adding H+.
5. Add sufficient electrons (e-)to one side of each half reaction to balance the charges. Electrons appear on the left in the reduction half reaction and appear on the right in the oxidation half reaction
6. Balance the electrons by finding a common factor for the electrons. Then multiply each half reactions by some integer so the # of electrons are the same in each half-reaction.
7. Add the two half-reactions, canceling and reducing any elements or compounds. The electrons should cancel on each side.
8. Check your work!
In Basic Solution Balance following “acidic”steps. Then two additional steps.
9. Add an equal number of OH- ions to both sides of the equation to “neutralize” H+ ions.
10. Cross out waters on each side
Standard Cell Potential
Just as the water tends to flow from a higher level to a lower level, electrons also move from a higher “potential” to a lower potential. This potential difference is called the electromotive force (EMF) of cell and is written as Ecell.
The standard for measuring the cell potentials is called a SHE (Standard Hydrogen Electrode).
Description of SHE (Standard Hydrogen Electrode)
Reaction 2H+(aq, 1M)+ 2e -à H2(g, 101kPa) E0= 0.00 V
Many different half cells can be paired with the SHE and the standard reduction potentials for each half cell is obtained. Check the table for values of reduction potential for various substances:
Metallic elements start out with a charge of ZERO, so they can only be oxidized to form (+) ions.
The higher of two metals MUST undergo oxidation in the reaction, or no reaction will happen
Some applications of Redox Reactions:
______is the oxidation of some metal caused by some substance in the environment. The common example is rusting of iron.
______A way to remove unwanted color from fabric or other materials. Color is caused by movement of electrons between different energy levels and bleaching removes these electrons. Bleaches are oxidizing agents. Two common bleaches are hypochlorite, ClO-, and hydrogen peroxide, H2O2.
______like gasoline, are oxidized by oxygen and form ______and ______
Explosives, like nitroglycerin (C3H5(NO3)3 contain both ______& ______agents.
Photography: Film processing is based on the oxidation of Bromide ions and the reduction of silver ions.
Voltaic (galvanic) / Electrolytic
Spontaneous
Anode
Cathode
# of cells
Salt bridge