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Topic 6.4 Redox Reactions - Coggle Diagram
Topic 6.4 Redox Reactions
Reduction
Example
Copper oxide upon heating forms pure copper
Definitions
The removal of oxygen in a substance
The loss of oxygen of a substance
The gain of electrons by a substance
The decrease in oxidation number of substance
Oxidation
Definitions
The addition of oxygen to a substance
Gain of oxygen of a substance
Loss of electrons by a substance
The increase in oxidation number of a substance
Examples
Combustion
Rusting
Note: Used only to describe the oxidation of iron
Other metals are corroded when they are oxidised
Dehydration
Oxidising Agent
Characteristics
Add oxygen to a substance
Remove electrons from a substance
Increase the oxidation number of a substance
Help oxidation take place
In the reaction, becomes reduced itself
Examples
Metal ions low in the reactivity series
Acidified potassium manganate solution KMNO4
Acidified potassium dichromate solution K2Cr2O7
Chlorine Cl2
Oxygen O2
Conc. sulfuric acid H2SO4
Conc. nitric acid HNO3
Test
Step 1: Add the unknown solution to a clean and dry test tube
Step 2: Add acidified potassium iodide solution to the test tube with the unknown solution
Observation: If the solution turned from colourless to reddish brown, the unknown solution is an oxidising agent
Picture shown below:
Strength
The more easily a substance
gains
electrons, the more powerful it is as an
oxidising agent
Redox Reactions
Definition- Redox reactions are reactions where oxidation and reduction are taking place
simultaneously
.
Note: In the reaction, the oxidising agent is itself
reduced
and the reducing agent is itself
oxidised
.
Examples
Aluminium + Oxygen = Aluminium Oxide
Sulfur Dioxide + Oxygen = Sulfur Trioxide
Applications in real life
Conversion of food and oxygen to carbon dioxide and water within the human body
Functioning of batteries in all electronic devices
Photosynthesis – reduction of carbon dioxide into sugars and the oxidation of water into molecular oxygen
Reducing Agent
Characteristics
Remove oxygen from a substance
Add electrons to a substance
Decrease the oxidation number of a substance
Helps reduction take place
In the reaction, becomes oxidised itself
Examples
Metals high in the reactivity series
Carbon C
Carbon Monoxide CO
Hydrogen H2
Hydrogen Sulfide H2S
Sulfur Dioxide SO2
Acidified potassium iodide solution KI
Strength
The more easily a substance
loses
electrons, the more powerful it is as an
reducing
agent
Test
Method 1
Step 1: Add the unknown solution into a clean and dry test tube.
Step 2: Add potassium dichromate solution acidified with dilute sulphuric acid into the test tube containing the unknown solution.
Observation: If the solution turned from orange to green, the unknown solution is a reducing agent. Picture shown below
Method 2
Step 1: Add the unknown solution into a clean and dry test tube
Step 2: Add acidified potassium manganate solution to the test tube containing the unknown solution.
Observation: If the solution turned from purple to colourless or pink, the unknown solution is a reducing agent. Picture shown below
Oxidation Numbers
Definition- the charge an atom of an element would have existed as an ion in a compound, even if it is actually covalent bonded.
Rules for assigning oxidation numbers
Rule 1: Oxidation numbers of atoms is an element is zero
Rule 2: Oxidation number of a simple ion is the charge on the ion
Rule 3: Oxidation number of hydrogen is +1 except metallic hydrides
Rule 4: Oxidation number of oxygen is -2 except in peroxides
Rule 5: Oxidation number of the atoms in the formula of a compound must add up to 0.
Rule 6: Sum of the oxidation numbers of the atoms in a polyatomic ion is equal to the charge on the ion.
