| |
| 1.1 |
Oxidation and Reduction |
|
| |
| The Term 'Redox' |
- ‘red’ from the reduction reaction and ‘ox’ from the oxidation reaction.
|
|
| |
| Definition of Redox Reaction |
- Redox reaction is the combination of oxidation and reduction reactions occurring simultaneously.
- Initially, a redox reaction refers to a reaction involving oxygen.
|
|
| |
 |
| |
 |
| |
| Oxidation Agent |
| The substance that is reduced in the redox reaction. |
|
| |
| Example of Oxidising Agents |
- Acidified potassium manganate(VII) solution.
- Acidified potassium dichromate(VI) solution.
- Chlorine water.
- Bromine water.
- Iron(III) ion.
|
|
| |
| Reducing Agents |
| The substance that is oxidised in the redox reaction. |
|
| |
| Example of Reducing Agents |
- Chloride ion.
- Bromide ion.
- Iodide ion.
- Sulphate ion.
- Sulphur dioxide gas.
- Hydrogen sulphide gas.
|
|
| |
| Oxidation Number or Oxidation State |
- The oxidation number of an element is the charge of an element if the element exists as an ion.
- Also known as oxidation state.
- The rules in assigning the oxidation number of an element are as follows;
|
|
| |
| Rule |
Example |
Oxidation Number |
| The oxidation number of elements as atom or molecule is zero. |
Natrium, \(Na\)
|
0 |
|
Gas klorin, \(Cl_2\)
|
0 |
| The oxidation number of simple ions is the charge of the ion. |
Ion natrium, \(Na^+\)
|
+1 |
| The total oxidation number of elements in a compound is zero. |
Ammonia, \(NH_3\)
|
0 |
| The total oxidation number of elements in a polyatomic ion is the same as the charge of the polyatomic ion. |
Ion sulfat, \(SO_4\, ^{2-}\)
|
-2 |
| The oxidation number of all elements in Group 1 is +1. |
Na dalam \(NaCl\)
|
+1 |
| The oxidation number of all elements in Group 2 is +2. |
Mg dalam \(MgCl_2\)
|
+2 |
| The oxidation number of all elements in Group 13 is +3. |
Al dalam \(Al_2O_3\)
|
+3 |
| The oxidation number of all elements in Group 17 is -1. |
Cl dalam \(NaCl\)
|
-1 |
| The oxidation number of oxygen in most of its compounds, except for hydrogen peroxide. |
O dalam \(Al_2O_3\)
|
-2 |
|
O dalam \(H_2O_2\)
|
-1 |
| The oxidation number of hydrogen in most of its compounds, except for metal hydride. |
H dalam \(HCl\)
|
+1 |
|
H dalam \(NaH\)
|
-1 |
|
| |
| Steps in Calculating the Oxidation Number of An Element in A Compound |
- Write the oxidation number of each element according to the rules.
- Use the symbol X to represent the unknown number.
|
- Multiply the oxidation number with the subscript of each element based on the molecular formula.
|
- Write the mathematical equation for the total oxidation number.
|
- Complete the mathematical equation to determine the unknown number.
|
|
| |
| IUPAC Naming System for Compounds |
- An ion can have a few oxidation numbers.
- For such ions, the oxidation number is written in the name of the compound to avoid confusion.
- If the oxidation number of an element is one, there is no need to write the oxidation number in the name of the atom or compound.
|
|
| |
| Redox Reaction in the Displacement of Metal from its Salt Solution |
- A more reactive metal displaces the metal or cation in a salt solution.
- This reaction is a redox reaction.
- The oxidation number of the cation in the salt solution is reduced, and the oxidation number of the more reactive metal is increased.
|
|
| |
|
Example: Addition of Zinc Plate into Copper(II) Nitrate, \(CuNO_3\) Solution
|
| Observation |
Inference |
- The intensity of blue colour of copper(II) nitrate solution decreases
|
- The concentration of copper(II) ion, \(Cu^{2+}\) decreases as the ion is reduced into solid
|
|
|
- Copper(II) ion is reduced
- \(Cu^{2+} (aq)+2e^- \rightarrow Cu(s)\)
|
- The zinc plate becomes thinner
|
- The zinc metal is oxidised as it releases electrons to form zinc ion
- \(Zn(s) \rightarrow Zn^{2+} + 2e^-\)
|
|
| |
