SCH4U - Introduction to Redox Reactions

Define an oxidation reaction. (1)

• the process in which one or more electrons is LOST by a chemical entity

Define a reduction reaction (1)

• the process in which one or more electrons is GAINED by a chemical entity

What is a mnemonic to remember the redox reactions?

• “LEO says GER”

What does the mnemonic “LEO says GER” stand for?

• LEO: lose electrons oxidise

• GER: gain electrons reduce

What does an oxidizing agent do?

• ACCEPTS electrons

• Undergoes REDUCTION

What does a reduction reaction do?

• DONATES electrons

• Undergoes OXIDATION 

Relate the redox agents to their corresponding redox reactions.

• Oxidizing agent undergoes Reduction reaction (accepts electrons)

• Reducing agent undergoes Oxidation reaction (donates electrons)

What is a half - reaction? define it. (1)

• A balanced equation that shows the number of electrons involved in either oxidation or reduction

How many half - reactions are needed to show a redox reaction?

• Two half reactions are needed to show a redox reaction

Can you have a reduction reaction without an oxidization reaction?

• No

Can you have an oxidization reaction without a reduction reaction?

• No

Recall the method / steps to writing half - reactions.

1. Separate the equation into two half-reaction equations for the reaction

2. Divide each equation by a whole number so that the coefficients in the equation are in the simplest whole number ratio

3. Add electrons to both equations so that the net charge on both sides of each equation is equal

4. Determine whether each half-reaction represents an oxidation or a reduction

What are oxidization numbers?

• Numbers used to keep track of electrons in redox reactions

What does the zero sum rule state in regards to oxidization numbers?

• ZERO SUM RULE: The SUM of the oxidation numbers of all atoms in a neutral compound must equal zero

  
  
  

What does the ion - charge rule state in regards to oxidization numbers?

• ION CHARGE RULE: The SUM of the oxidation numbers of all atoms in polyatomic ions must equal the overall charge of the ion

Recall how to assign oxidation numbers for different elements and ions. (remember the class - posted table).

Recall the rules for assigning oxidation numbers to

1. Assign oxidation numbers to elements as listed in the table

2. Identify any elements not mentioned in the table, and use the ZERO SUM rule or ION CHARGE rule to assign their oxidation numbers

3. Check that the sum of the oxidation numbers is equal to zero (neutral) or the charge (polyatomic ion)