discussion oxidation- reduction reaction

Period 1
11/7/13
Chapter 35 Discussion
Background:
Potassium permanaganate is widely used as an oxidizing agent in volumetric analysis. In acid solution, MnO4- ion undergoes reduction to Mn2+ this is the equation:
8H+(aq) + Mno4-(aq) + 5e-  Mn2+(aq) + 4H2O
Since the KMnO4 – ion is violet and the Mn2+ ion is nearly colorless, the end point titrations using KMnO4 as the titrant can be taken as the first pink color that appears in the solution (and stays without disappearing). The titration which involves the oxidation of Fe2+ ion to Fe3+ by permanganate ion, is carried out in sulfuric acid to prevent air-oxidation of Fe2+ (we can them determine the accurate number of oxygen reacted this way).
MnO4- in KMnO4  Oxidizing agent; it is reduced
Fe in Fe(NH4)2(SO4)2● 6H2O Reducing agent; it is oxidized

Objective: To determine the percentage of iron in an unknown containing iron (II) ammonium sulfate Fe(NH4)2(SO4)2● 6H2O
How to find the percentage (%) magnesium by mass:
Balance the equation get the moles of KMnO4  get moles of MnO4-  get moles of Fe2+ get grams of Fe2+  get molar mass of Fe(NH4)2(SO4)2● 6H2O find grams per mole ratio of Fe2+ and Fe(NH4)2(SO4)2● 6H2O multiply by 100%  % of Fe2+

Experimental errors:
1. Volume of KMno4 lost because it splashed and stayed at the side of the beaker:
Increased volume of KMno4 used  increased moles of KMno4  increased moles of Fe2+  increased grams of Fe2+ increased percentage of Fe 2= in sample

2. Diluting the KMno4 with water because of careless cleaning of the buret;
Diluting the KMnO4 with water  decreased molarity of KMno4 increased volume of KMn04 used decreased mole of KMnO4 decreased mole of MnO4 decreased mole of Fe2+ decreased mass of Fe2+  decreased percentage of Fe2+