Download Redox reaction Oxidizing agent

• both atoms and the electrons must be balanced
in redox reactions
gains 1e- x 2 atoms = 2eoxidation numbers:
0
2 Cu
0
+
+1
-1
Cl2 → 2Cu+ + 2 Clloses 1e- x 2 = 2e-
• done by assigning oxidation numbers to all
elements
**There is a written difference between ion charge and
oxidation number**
Mg (s) + Cl2 (g) → MgCl2 (s)
Mg → Mg2+ + 2eMagnesium ion
ion charge: 2+
oxidation #: +2
Cl + 1e- → Cl1Chlorine ion
ion charge: 1oxidation #: -1
Sometimes these numbers are the same (like above) sometimes they are
very different – which is why we write them differently
Oxidation number represents the charge the atom
would have if every bond were ionic.
O#s are based on the electronegativity of the atoms
1. Assign known numbers first, calculate others.
• All uncombined elements (& diatomics) – zero
O2
0
Cu
0
• Monatomic ion - equals ion charge
Fe3+
+3
Cl-
-1
•
•
•
•
•
Alkali metals (IA) – always +1
Earth metals (IIA) – always +2
Halogens (VIA) – usually -1
Hydrogen – usually +1 Except metal hydrides (NaH)
Except peroxides (H O )
Oxygen – usually -2
2
2
2. Neutral compound:
• Sum of O#s must equal zero
3. Charged compound:
• Sum of O#s must equal charge of compound
2. Neutral compound:
•
Sum of O# must equal zero
Assign O#s for each atom in K2Cr2O7
Step 1: Start with atoms which are known.
O: –2
K: +1
Step 2: Solve for other atoms.
+1 +6 -2
K2Cr2O7
Multiple the O#s by the
subscripts for each atom to
get the sum
+2 +12
?? -14 = 0
K = +1
Cr = +6
O = –2.
3. Charged compound:
•
Sum of O# must equal charge of compound
Assign O#s for each atom in NO3Step 1: Start with atoms which are known.
O: –2
Step 2: Solve for other atoms.
+5 -2
NO3+5
?? -6 = -1
N = +5
O = –2.
Use ox.numbers to determine if reaction is a
redox reaction.
+4 -2
+1 -2
+1 +4 -2
+4 -4
+2 -2
+2 +4 -6
SO2 + H2O → H2SO3
Remember: Redox involves the transfer of electrons – no change in O#s during
the reaction means NO redox
NOT a redox reaction
Is the following reaction a redox reaction?
0
+1 +5 -2
+1 +5 -2
0
0
+1 +5 -6
+1 +5 -6
0
Cu(s) + 2 AgNO3(aq) → CuNO3(aq) + 2 Ag(s)
Oxidation cannot occur without reduction
Redox reaction
• Cu – oxidized (loss of electrons)
• Ag – reduced (gain of electrons)
Oxidizing agent - causes the oxidation of another
substance. AgNO3 is the oxidizing agent
Reducing agent - causes the reduction of another
substance.
Cu is the reducing agent
Think opposites: if the compound is the “oxidizing agent” of the reaction, then it
is reduced in the process and vice versa
+1
0
Cu(s) + 2 AgNO3(aq) → CuNO3(aq) + 2 Ag(s)
+1
0
Identify the substance oxidized, the substance
reduced, the oxidizing agent and the reducing agent.
+1 +5 -2
+1 -2
+2 -2
0
+1 -2
+1 +5 -6
+2 -2
+2 -2
0
+2 -2
2 HNO3(aq) + 3 H2S(g) → 2 NO(g) + 3 S(s) + 4 H2O(l)
S – oxidized
N – reduced
H2S – reducing agent
HNO3 – oxidizing agent
Substance - means element
Agent – means compound
How many electrons are transferred in the reaction
below:
gains 3e-
+1 +5 -2
+1 -2
+2 -2
0
+1 -2
2 HNO3(aq) + 3 H2S(g) → 2 NO(g) + 3 S(s) + 4 H2O(l)
loses 2eStoichiometry (coefficients and subscripts) used to determined
total electrons transferred
S: (3 atoms) x (2e- lost) = 6 electrons lost
N: (2 atoms) x (3e- gained) = 6 electrons gained
CAN YOU / HAVE YOU?
• Determine the oxidation numbers for atoms in
compounds and ions
• Identify reactions as redox or non-redox
Include: oxidizing agent, reducing agent
Additional KEY Terms