# Question & Answer: II. Determination of Unknown Concentration Procedure: Add 1.2 mL of unknown Fe (II) solution…..

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

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