1. Redox reactions involve the transfer of electrons from one reactant to another. The substance that loses electrons is oxidized and is the reducing agent, while the substance that gains electrons is reduced and is the oxidizing agent. 2. To determine if a substance is reduced or oxidized, ask if it gains or loses electrons. Gaining electrons means it is reduced, while losing electrons means it is oxidized. 3. An example reaction of ethane burning in oxygen is worked through to assign oxidation numbers, determine which substances gain or lose electrons, and identify the reducing and oxidizing agents.

1. Tutorial and Practice
Redox Reactions

2. Review
 Redox reactions involve the transfer of electrons
from one reactant to another
 When there is oxidation, there is also reduction
 The substance that loses electrons= oxidized and
is reducing agent
 The substance that gains electrons= reduced and
is oxidizing agent

3. 2 questions to ask
 Does one gain electrons? If yes, then it has been
reduced
 Does one lose electrons? If no, then it has been
oxidized

4. Example
Ethane burns in oxygen:
C2H6 + O2  CO2 + H2O
Steps:
1. Assign oxidation numbers (in red)
C2
-3H6
+1 + O2
0  C +4O2
-2 + H2
+1O-2

5. Steps continued
2. Write down which ones gain and which ones lose
electrons
 Oxygen gained electrons (0 charge to -2 charge)
 C lost electrons (-3 charge to +4 charge)
3. Determine which one is reduced and is the oxidizing
agent
 Oxygen is reduced and is the oxidizing agent
4. Determine which one is oxidized and is the reducing
agent
 Carbon is oxidized and the reducing agent

6. Practice
Try out the 4 steps on the reaction below:
Cl2 + 2KI  I2 + 2KCl
Go to next slide to see if you are correct!

7. 1. Assign Oxidation numbers:
Cl2
0 + 2K +1I -1  I2
0 + 2K +1Cl -1
2. Which ones gain and which ones lose electrons:
 Cl gains electrons
 I loses electrons
3. Determine which one is reduced and is the
oxidizing agent
 Cl is reduced and is the oxidizing agent
4. Determine which one is oxidized and is the
reducing agent
 I is oxidized and is the reducing agent