Card Set Information
chem redux reactions
Oxidation Reduction Reaction
Reactions involving the transfer of electrons
must have a metal and a non-metal for electrons to transfer
Cumbustion reactions are also "Oxidization"
Describes how many electrons have been lost or gained by an atom
we must use oxidation numbers to keep track of the partial gain or loss of electrons by an atom in a molecular compound
Oxidation Number Rule 1-2
Oxidation numberes are assigned according to seven rules:
1. a metal or a non metal in the
has an oxidation number of 0
2. A monoatomic ion has an oxidation number equal to it's ionic charge
3. A hydrogen atom is usually assigned an oxidation number of 1+
4.An oxygen atom is ALWAYS assigned an oxidation number of -2
5. For the
molecular compouind (covalent/non-metal),
the more electronegative element is assigned a negative oxidation number equal to it's sharge as an anion (tricky
compound, the sum of the oxidation numbers for each of the stoms in the compounds is equal to 0
for a polyatomic ion, the sum of the oxidation number for each of the atoms in the compound is equal to the iconic charge on the polyatomic ion
For each molecule, the sum of the oxidation numbers for each of the atoms in the compound is equal to 0
Rules 6,7,8 all the same rule.
Note: If there is a conflict in these rules, the rule with the lowest number has priority!
Free state of elements - rule 1
Seven non metals occur naturally as diatomic molecules
they are: hydrogen (H
), Oxygen (O
A chemical reaction that involves the transfer of electrons in an oxidation reducyion reaction.
Iron loses electrons
The sulfur gains electrons and is
is the loss of electrons and
is a substance that causes oxidation by accepting electrons. The oxidating agent is reduced
Is a substance that causes reduction by donating electrons. The reducing agent is oxidized
Ways to rememebr What oxidation and reduction mean
"LEO the lion says GER
, one substance must be oxidized and one substance must be reduced (these always happen simutaneously)
number of electrons lost is equal to the total electrons gain
•Redox reactions in aqueous solution are most often shown in the ionic form because ionic equations easily show us the change in oxidation number.
Ionic Equations Continued
•We map out the reaction to show the oxidation and reduction processes and to determine the oxidizing and reducing agents.
•We can easily tell that the oxidation number of iron changes from +2 to +3; iron is oxidized.
•Manganese is reduced from +7 in MnO4- to +2 in Mn2+; manganese is reduced.
Balancing Redox Reactions
When we balance redox reactions, the number of electrons lost must always equal the number of electrons gained
There are two ways to balance redox reactions:
1. The oxidation Number Method
2. Half-Reaction Method
Balancing Redox Reactions
Oxidation Number Method three steps
1. Inspect the reaction and the substances undergoing a change in oxidation number
a) Write the number above each element
b) Diagram the number of electrons lost by the oxidized substance and gained by the reduced substance
Oxidation Number Method
2. Balanc each element in the equation using a coefficient. Remember , that the electrons lost must equal the electrons gained. If they are not the same, balance the electrons as follows
how to balance electrons
a)In front of the oxidized substance, place a coefficient equal to the total number of electrons gained by the reduced substance.
b)In front of the reduced substance, place a coefficient equal to the total number of electrons lost by the oxidized substance.Balance the remaining elements by inspection
Oxidation Number Method
3.After balancing the equation, verify that the coefficients are correct.
a)Place a check mark above the symbol for each element to verify that the number of atoms is the same on both sides.
b)For ionic equations, verify that the total charge on the left side of the equation is the same as the total charge on the right side of the equation.
Half- Reaction Method
an alternative method for balanching redox reactions is the
a half reaction
shows the oxidation or reduction process of redox reaction separately
the oxidation half of the reaction is balanced forst then the reducation half of the reaction is balanced second
5 steps to balance
1. write the half reaction for both the oxidation and reduction processes separately
a) identify the reaction that is oxidized and its product
b) Identify the reactant that is reduced and its product
Half-Reaction step 2
Balance the atoms in each half-reaction using coefficients
a)balance all elements except O andH
b) balance O using H
c) balance H using H
d) for reactions in a basic solution, add one OH-
to each side to neutralize each H
Step 3 half reaction
Multiply each half-reaction by whole number so that the total # of e
's lost by oxidation equal the total# e
s gained by reduction
Step 4 Half reaction
4.Add the two half-reactions together and cancel the identical species, including electrons on each side of the equation.
Step 5 half reaction
5.After balancing, verify that the coefficients are correct by making sure there are the same number of each atom on each side of the reaction and that the overall charge is the same on both sides.
•A redox reaction is a reaction involving the transfer of electrons from one substance to another.
•The oxidation number describes how many electrons have been lost or gained by an atom.
•Oxidation is the loss of electrons.
•Reduction is the gain of electrons.
•An oxidizing agent is a substance that causes oxidation by accepting electrons. The oxidizing agent is reduced.
•A reducing agent is a substance that causes reduction by donating electrons. The reducing agent is oxidized.
In redox reactions, the number of electrons lost must equal the number of electrons gained
•There are two methods to balance redox reactions:
–The Oxidation Number Method
–The Half-Reaction Method