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 ___________________________eA 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 halfreactions (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 - 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.
A voltaic cell converts chemical energy from a
______________________________ redox reaction into electrical
energy.
A reaction is spontaneous if the metal with higher
reduction potential (______________________ on activity series)
is made the cathode.
Higher on activity series = (-) anode
(lower reduction potential)
Lower on activity series = (+) cathode
(higher reduction potential)
An ______________________________ cell uses electricity to
force a ________________________________ redox reaction to
take place.
Voltaic
(galvanic)
Spontaneous
Anode
Cathode
# of cells
Salt bridge
Electrolytic