1) Table A. Standardization of the 0.02 M KMnO 4 solution with Fe(NH 4 ) 2 (SO 4

Question

1)

Table A. Standardization of the 0.02 M KMnO4 solution with Fe(NH4)2(SO4)2 · 6H2O.
(Molecular weight of the ferrous sulfate hexahydrate is 392.16 g/mol).

If you weigh out 1.66 g of the Fe(NH4)2(SO4)2 · 6H2O, how many moles of iron (Fe+2) are in the sample?
(Free Hint: for every mole of Fe(NH4)2(SO4)2· 6 H2O, how many moles of Fe+2 are there? Yes, it's a one-to-one ratio!)

0.00423 moles

2)

Assume you fill a buret with your KMnO4 solution and the volume initally reads 0.15 mL (don't waste your time trying to fill it drip by drip to exactly 0.00 mL, just record the starting volume). After you use the KMnO4 solution to titrate your iron sample you notice the buret then reads 27.08 mL.

What is the volume of KMnO4 used?

26.93 mL

3)

How will you know when the titration reaction is done and to stop titrating KMnO4 into the sample solution?

The first drop of excess KMnO4 will leave a pink color

4)

Looking at the stoichiometry of the reaction (see the lab manual), how many moles KMnO4 must have been delivered by the buret to react with that much Fe(NH4)2(SO4)2 · 6H2O? 8H+ + 5Fe+2 + MnO4 - --> Mn+2 + 5Fe+3 + 4H2O (Remember that all Group I salts are soluble - including KMnO4. Therefore moles KMnO4 = moles MnO4 -) Looking at the stoichiometry of the reaction (see the lab manual), how many moles KMnO4 must have been delivered by the buret to react with that much Fe(NH4)2(SO4)2 · 6H2O? 8H+ + 5Fe+2 + MnO4 - --> Mn+2 + 5Fe+3 + 4H2O (Remember that all Group I salts are soluble - including KMnO4. Therefore moles KMnO4 = moles MnO4 -)

8.47×1004 moles

4.23×1003 moles

1.85×1003 moles

Part B)

Considering the moles and volume of KMnO4 above, what must the true molarity of your KMnO4 solution be?

2.07×1002 M

3.14×1002 M

1.05×1002 M

0.00423 moles

2)

Assume you fill a buret with your KMnO4 solution and the volume initally reads 0.15 mL (don't waste your time trying to fill it drip by drip to exactly 0.00 mL, just record the starting volume). After you use the KMnO4 solution to titrate your iron sample you notice the buret then reads 27.08 mL.

What is the volume of KMnO4 used?

26.93 mL

3)

How will you know when the titration reaction is done and to stop titrating KMnO4 into the sample solution?

The first drop of excess KMnO4 will leave a pink color

4)

Explanation / Answer

Solution-

1)

1.66 g / 392.16 g/mol = 0.00423

mol Fe(NH4)2(SO4)2 and since 1 mole of Fe(NH4)2(SO4)2 contains 1 mole of Fe^+2,

your answer is 0.00423 mol Fe^+2.

2) 27.08 - 0.15 = 26.93 mL KMnO4 used.

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