3.1.7 Oxidation, Reduction and redox reactions Flashcards
What are oxidation states
Tells the number of electrons that an element has accepted or donated
Rules for calculating oxidation states
★Uncombined elements/elements bonded to elements of the same type (O2) =0
★In a compound, the sum of oxidation states is 0
★In a complex ion, the sum of oxidation states in the charge
★oxidation states of elements in group 1 metals in a compound is +1
★Oxidation states of group 2 metals in a compound is +2
★Aluminium in a compound =+3
★Hydrogen in a compound = +1 (except in a metal hydride ,e.g.CaH2, where it is -1
★oxygen in a compound is -2 (except in a peroxide ,e.g.H2O2 where it is -1)
Oxidation state of uncombined elements or elements bonded to the same type of element
0
Sum of oxidation states in a compound
0
Sum of oxidation states in a complex ion
Same as charge
oxidation states of group 1 ,metals
+1
oxidation states of group 2 metals
+2
oxidation states of aluminium
+3
oxidation states of hydrogen in a compound
+1
oxidation states of hydrogen in a metal hydride
-1
oxidation state of oxygen in a compound
-2
oxidation states of oxygen in a peroxide
-1
Rules for building half equations
★Balance the atoms that are not oxygen or hydrogen
★Balance oxygens through the addition of water
★balance hydrogens through the addition of H⁺ ions
★Balance charge by adding electrons
OIL RIG
oxidation is loss, reduction is gain
Oxidation
A reaction in which an atom or group of atoms loses electrons
Reducing agent
An electron donor
Reduction
A reaction in which an atom or group of atoms gains electrons
Oxidising agent
An electron acceptor
Label the elements
Mg + Cu²⁺ –> Mg²⁺ + Cu
Mg= Reducing agent
Mg –>. Mg²⁺ is oxidation
Cu²⁺=oxidising agent
Cu²⁺ –> Cu =Reduction
If oxidation state decreases (in a half equation)
Reduction
If oxidation state increases (in a half equation)
Oxidation
Rules for combining half equations
- One half equation must show oxidation, the other must show reduction
- Before combining them, the number of electrons in each half equation must be equal
3.Add equations together
- remove any spectator ions or electrons
How to tell if a equation represents a redox reaction
if oxidation numbers change
CH₄ + O₂ -> CO₂ + H₂O
-4, +4 0 +4, -2 +1, -2
