Has a Redox Reaction Occurred?
So, who cares about oxidation numbers? Well, we can use them to determine if a reaction is an oxidation/reduction reaction. This would mean that electrons are being exchanged, and the movement of electrons is electricity. Not so pointless now, is it?
In fact, we say a redox reaction has occurred if the oxidation numbers of atoms change between reactants and products.
If an atom's oxidation number increases, it has been oxidized.
If an atom's oxidation number decreases, it has been reduced.
In fact, we say a redox reaction has occurred if the oxidation numbers of atoms change between reactants and products.
If an atom's oxidation number increases, it has been oxidized.
If an atom's oxidation number decreases, it has been reduced.
Questions (from Nelson Chemistry 12)
For each of the following chemical reactions, assign oxidation numbers to each atom/ion and indicate whether the equation represents a redox reaction. If it does, identify the oxidation and reduction.
(a) Cu(s) + 2 AgNO3(aq) → 2 Ag(s) + Cu(NO3)2(aq)
(b) Pb(NO3)2(aq) + 2 KI(aq) → PbI2(s) + 2 KNO3(aq)
(c) Cl2(aq) + 2 KI(aq) → I2(s) + 2 KCl(aq)
(d) 2 NaCl(l) → 2 Na(l) + Cl2(g)
Answers
a) Cu changes from 0 to +2 (oxidized). Ag changes from +1 to 0 (reduced)
b) Pb starts as +2 and remains +2. K starts as +1 and remains +1. No redox reaction has occurred.
c) Cl changes from 0 to -1 (reduced). I changes from -1 to 0 (oxidized)
d) Na changes from +1 to 0 (reduced). Cl changes from -1 to 0 (oxidized)
(a) Cu(s) + 2 AgNO3(aq) → 2 Ag(s) + Cu(NO3)2(aq)
(b) Pb(NO3)2(aq) + 2 KI(aq) → PbI2(s) + 2 KNO3(aq)
(c) Cl2(aq) + 2 KI(aq) → I2(s) + 2 KCl(aq)
(d) 2 NaCl(l) → 2 Na(l) + Cl2(g)
Answers
a) Cu changes from 0 to +2 (oxidized). Ag changes from +1 to 0 (reduced)
b) Pb starts as +2 and remains +2. K starts as +1 and remains +1. No redox reaction has occurred.
c) Cl changes from 0 to -1 (reduced). I changes from -1 to 0 (oxidized)
d) Na changes from +1 to 0 (reduced). Cl changes from -1 to 0 (oxidized)
