Is it a redox reaction?

1. REDOX REACTIONS USING
OXIDATION NUMBERS

2. Identifying Redox Reactions
The change in oxidation number can be
used to identify whether each reaction is a
redox reaction or a reaction of some other
type.
If a reaction is a redox reaction, identify the
element reduced, the element oxidized.
a. Cl2(g) + 2NaBr(aq) → 2NaCl(aq) + Br2(aq)
b. 2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l)

3. Applying oxidation numbers to the equation
a. Assign oxidation numbers.
0 +1 –1 +1 –1 0
Cl2(g) + 2NaBr(aq) → 2NaCl(aq) + Br2(aq)
If changes in oxidation number occur, the
reaction is a redox reaction

4. The oxidation numbers have increased and decreased for
bromine and chlorine respectively
• This is a redox reaction.
• The chlorine is reduced.
• The bromide ion is oxidized.
0 +1 –1 +1 –1 0
Cl2(g) + 2NaBr(aq) → 2NaCl(aq) + Br2(aq)

5. Let us look at another example.
Assign oxidation numbers.
+1 –2 +1 +1 +6 –2 +1 +6 –1 +1 –2
2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l)

6. Calculate the change (if any) in the oxidation numbers
• There was no change in any of the elements oxidation numbers.
• This is not a redox reaction.
+1 –2 +1 +1 +6 –2 +1 +6 –1 +1 –2
2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l)

7. Which of the following are redox reactions?
1. NH3 + HCl → NH4Cl
2. SO3 + H2O → H2SO4
3. NaOH + HCl → NaCl + H2O
4. H2S + NHO3 → H2SO4 + NO2 + H2O

8. Did you get them correct?
1. NH3 + HCl → NH4Cl
2. SO3 + H2O → H2SO4
3. NaOH + HCl → NaCl + H2O
4. H2S + NHO3 → H2SO4 + NO2 + H2O