Redox Titration

CHEMISTRY 205
REDOX TITRATIONA. Purpose:
• To learn some technique in volumetric analysis: Redox titration.
• To review the stoichiometry of an oxidation- reduction reaction.
• To determine the concentration of an unknown sodium oxalate (Na2C2O4) solution by titrating it against standardized potassium permanganate solution (KMnO4).
• To determine the percent by mass of Fe(II) in the form of ferrous ammonium sulfate
Fe(NH4)2(SO4)2.6H2O in a mixture by redox titration. B. Theory:
(electron transfer reactions)
2Mg (s) + O2 (g) 2MgO (s)
2Mg 2Mg2+ + 4e-
O2 + 4e-
2O2-
Oxidation half-reaction (lose e-
)
Reduction half-reaction (gain e-
)
2Mg + O2 + 4e-
2Mg2+ + 2O2-
+ 4e-
2Mg + O2 2MgO
* Copyright: The McGraw-Hill Companies, Inc.
Oxidation-Reduction Reactions*Zn (s) + CuSO4 (aq) ZnSO4
(aq) + Cu (s)
Zn is oxidized, Zn Zn2+ + 2e-
Cu2+ is reduced, Cu2+ + 2e-
Cu
Zn is the reducing agent
Cu2+ is the oxidizing agent
Copper wire reacts with silver nitrate to form silver metal.
What is the oxidizing agent in the reaction?
Cu (s) + 2AgNO3 (aq) Cu(NO3)2
(aq) + 2Ag (s)
Cu Cu2+ + 2e-
Ag+ + 1e-
Ag Ag+ is reduced, Ag+ is the oxidizing agentOxidation number*:
The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred.
1. Free elements (uncombined state) have an oxidation number of zero.
Na, Be, K, Pb, H2, O2, P4 = 0
2. In monatomic ions, the oxidation number is equal to the charge on the ion.
Li
+, Li = +1; Fe3+, Fe = +3; O2-
, O = -2
3. The oxidation number of oxygen is usually –2. In
H2O2
and O2
2-
it is –1.
* Copyright: The McGraw-Hill Companies, Inc.4. The oxidation number of hydrogen is +1 except when it is bonded to metals in binary compounds.
In these cases, its oxidation number is –1.
6. The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to