The spectator ions (those that do not change) are SO4^2-(aq
These can be removed and the ionic equation written as: Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
By analysing the ionic equation, we can split the reaction into two half equations by adding in the electrons to show how the changes in charge have occurred:
Zn(s) → Zn2+(aq) + 2e-
Cu2+(aq) +2e- → Cu(s)
It then becomes clear that zinc has been oxidised as it has lost electrons
Copper ions have been reduced as they have gained electrons
Use the mnemonic OIL-RIG to remember oxidation and reduction in terms of the movement of electrons: Oxidation Is Loss – Reduction Is Gain.
Table of rules assigning oxidation numbers
A) oxidation number
B) element
C) zero
D) atoms
E) ions
F) fixed oxidation
G) number
H) compounds
I) +1
J) +2
K) -1
L) +1
M) -1
N) -2
O) -1
P) +2
Q) oxidation number
R) element
S) mono-atomic
T) ion
U) charge
V) +2
W) +3
X) -1
Y) sum
Z) oxidation number
[) zero
\) +1
]) -1
^) 0
_) sum
`) oxidation
a) number
b) ion
c) equal
d) charge on the ion
e) +6
f) 4 x -2
g) -2
Redox reactions can be identified by the changes in the oxidation number when a reactant goes to a product
The tests for redox reactions involve the observation of a colour change in the solution being analysed
e.g. acidified potassium manganate(VII), and potassium iodide
Potassiummanganate(VII), KMnO4, is an oxidisingagent which is often used to test for the presence of reducingagents
When acidifiedpotassiummanganate(VII) is added to a reducingagent its colour changes from purple to colourless
A) unknown
B) potassium
C) manganate
D) purple colour fades
E) reducing
F) agent
Potassiumiodide, KI, is a reducingagent which is often used to test for the presence of oxidisingagents
A) acidified
B) hydrogen peroxide
C) oxidising
D) red-brown
E) potassium
F) iodide
G) oxidised
H) oxidising agent
I) iodine
J) potassium
K) iodide
When added to an acidified solution of an oxidising agent such as aqueous chlorine or hydrogen peroxide (H2O2), the solution turns a red-brown colour due to the formation of iodine, I2:
The potassium iodide is oxidised as it loses electrons and hydrogen peroxide is reduced, therefore potassium iodide is acting as a reducing agent as it will itself be oxidised:
2I- → I2 + 2e-
Oxidising agent - a substance that oxidises another substance, and becomes reduced in the process
An oxidising agent gains electrons as another substance loses electrons
Common examples include hydrogen peroxide, fluorine and chlorine
Reducing agent - A substance that reduces another substance, and becomes oxidised in the process
A reducing agent loses electrons as another substance gains electrons
Common examples include carbon and hydrogen
The process of reduction is very important in the chemical industry as a means of extracting metals from their ores