tags:
- chem
topic: Redox
date: 2023-10-23
Introduction
- Multiple oxidation states exist for elements depending on their state of matter, existence as an ion, what it reacts with etc.
- For this reason, oxidation numbers can be used to determine whether a redox reaction has occurred.
- This is done by comparing the oxidation number of an element before and after the reaction.
- If the oxidation number has increased, that substance has been oxidised.
- Similarly, if it has decreased, the substance has been reduced.
Oxidation Number Rules
- The oxidation number of an element is zero.
- The oxidation number of a monatomic ion is equivalent to its charge.
- Hydrogen's oxidation number is +1 (except when reacting with a metal (-1), as a metal hydride)
- Oxygen's oxidation number is -2 (except when as a peroxide (-1))
- Oxidation numbers in covalent and ionic compounds add to zero.
- The total oxidation number for a polyatomic ion must add to the ion's total charge. Refer to steps 3. and 4. primarily when determining this.
- Oxidation number charges go in front of the number, not after
Examples
- Determine the oxidation number of the underlined element.
- (0) [Rule 1]
- (+3) [Rule 5]
- (+4) [Rule 4, Rule 5]
- (-4) [Rule 3, Rule 5]
- (+6) [Rule 4, Rule 6]