Warmup 2/23/16
What is an oxidizer again?
Oxidizers are usually very reactive. Why do you think this
is?
Objective
Tonight’s Homework
To learn how to identify redox
reactions
Finish Worksheet
Notes on Identifying Redox Reactions
With the last lesson or two, we’re more
equipped to identify redox reactions.
Let’s review the rules we’ve said and do a bit of
practice as a class.
Notes on Identifying Redox Reactions
With the last lesson or two, we’re more
equipped to identify redox reactions. Let’s
review the rules we’ve said and do a bit of
practice as a class.
1) An oxidizing agent: This is the substance in
the reaction that will gain electrons.
2) A reducing agent: This is the substance in
the reaction that will lose electrons.
These are always reactants, not products.
We can tell if something has lost or gained
electrons based on oxidation number before and
after the reaction.
Notes on Identifying Redox Reactions
Example: Determine whether the reaction below
is redox or not. If it is redox, identify the
oxidizing and reducing agents.
C H4(g) + 2O2(g)  C O2(g) + 2H2 O(g)
Notes on Identifying Redox Reactions
Example: Determine whether the reaction below
is redox or not. If it is redox, identify the
oxidizing and reducing agents.
C H4(g) + 2O2(g)  C O2(g) + 2H2 O(g)
-4 +1
0
+4 -2
+1
-2
Rule 4 for hydrogen,
Rule 6 for carbon
Rule 1
Rule 3 for oxygen,
Rule 6 for carbon
Rule 3 for oxygen,
Rule 4 for hydrogen
Notes on Identifying Redox Reactions
C H4(g) + 2O2(g)  C O2(g) + 2H2 O(g)
-4 +1
0
+4 -2
+1
-2
Ok. So is this redox?
Let’s look at carbon.
On the left side, C has an oxidation of -4.
On the right side, C has an oxidation of +4.
This is redox because something changed.
- CH4 is the reducing agent. It lost electrons.
- O2 is the oxidizing agent. It gained electrons.
Notes on Identifying Redox Reactions
A few last things to note:
1) We can have one chemical be both the
oxidizing agent AND the reducing agent. We see
this sort of thing in a synthesis reaction.
2) We can also gain or lose partial charges.
Technically, it just means electrons are being
split unevenly between atoms, but the math will
come out to show fractions of electrons. It’s ok.
3) If the number of atoms of a redox element
changes from reactant to product, the number
of electrons needs to be multiplied or divided to
make sure we get the same overall charge.
Practicing Identifying Redox Reactions
Let’s practice redox reactions.
For each of the reactions on the worksheet, do the
following:
- Identify whether or not the reaction is redox
- List the oxidation number for each element
- Identify the oxidation and reduction agents
Mr. C. will go over a few of these, even if we need to spill
into tomorrow a bit.
Practicing Identifying Redox Reactions
1)
2Na + FeCl2  2NaCl + Fe
2)
2C2H2 + 5O2  4CO2 + 2H2O
3)
2PbS + 3O2  2SO2 + 2PbO
4)
2H2 + O2  2H2O
5)
Cu + HNO3  CuNO3 + H2
6)
AgNO3 + Cu  CuNO3 + Ag
Exit Question
What is the oxidizing agent?
a) The substance that will lose electrons
b) The substance that will gain electrons
c) The substance that has lost electrons
d) The substance that has gained electrons
e) It depends on the reaction
f) None of the above