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II. Determination of Unknown Concentration
Procedure:
Add 1.2 mL of unknown Fe (II) solution into an Erlenmeyer flask along with 20.0 mL DI H2O, 1.0 mL 9 M H2SO4, 2 drops 0.1 M MnSO4, and 1 drop of 3 M phosphoric acid (H3PO4). Use a graduated pipet with 0.02 M KMnO4 to titrate solution.
1. Volume of Fe(II) solution used- 1.2 mL
2. Volume of KMnO4 solution used- 1.28 mL —– this is the amount of KMnO4 that was used to turn solution a pink color
*3. Balance the following chemical reaction
__MnO4– + __Fe+2 + __H+ —–> __Mn+2 + __Fe+3 + __H2O
*4. Calculate the molarity of the Fe(II) solution. _________ M
Expert Answer
Moles of KMnO4 used = Molarity*Volume = 0.02*(1.28/1000) = 0.0000256
The balanced reaction is:
MnO4– + 5Fe2+ + 8H+ —–> Mn2+ + 5Fe3+ + 4H2O
1 moles MnO4– need 5 moles Fe2+
So,
0.0000256 moles need: 0.0000256*5 = 0.000128 moles Fe2+
So, unknown molarity = moles/volume = 0.000128/(1.2/1000) = 0.1067 M
