Background

1

• Background
• K3Fe(C2O4)3 ?
  3H2O
• Potassium Trioxalatoferrate (III) Trihydrate was
  prepared in a previous experient.
• This compound is photosensitive.
• In acid solution (acetic acid in this case) in
  the presence of sunlight the reaction results in
  the reduction of Iron (Fe3 to Fe2) and the
  oxidation of an oxalate ligand to carbon dioxide
  as follows
• Reduction of Iron (Gain of Electrons)
• Half Cell Reaction Fe3
  e- ? Fe2
• Oxidation of Oxalate (Loss of Electrons)
• Half Cell Reaction (C2O4)2- ?
  2CO2 2 e-

2

• Background (Cont)
• In acidic solution, the Ferric (Fe3) ion is
  coordinated with one (1) oxalate ion.
  Fe3) (C2O4)2-
• In sunlight the coordinated oxalate is oxidized
  (loses an electron) reducing the ferric ion to
  the ferrous (Fe2) ion.
• Ferrous Iron (Fe2) is sparingly soluble and
  forms a yellow precipitate of ferrous oxalate
  dihydrate.
• Some of the oxalate (C2O4)2- is oxidized to CO2
• 2 Fe3(C2O4)2- (C2O4)2- 4H2O ?
  2 Fe2(C2O4)2- ? 2H2O 2CO2
• The overall ferrioxalate photoredox reaction is
• 2K3Fe3(C2O4)3 ? 3H2O H2O H ?
  2Fe2(C2O4) ? 2H2O 2CO2 3K2(C2O4)

3

• Procedure
• Week One End of Redox Lab Session
• Precisely weigh about 1 gram of the potassium
  trioxalatoferrate complex to the nearest 0.001g
  and mix with 15 mL of 10 (v/v) acetic acid.
• Place in sunlight for one week.
• A yellow precipitate should have formed.

4

• Procedure (Cont)
• Week Two
• You will be doing a vacuum filtration with a
  glass filter crucible instead of the normal
  Buchner funnel.
• Note The glass filter is delicate, treat
  with care.
• Pre-dry the glass filter crucible under lamp or
  in oven.
• Weigh the dried glass filter crucible.
  Note Use same balance for all weight
  determinations.
• Vigorously stir contents of test tube containing
  sample with a glass stirring rod.
• Pour quickly into glass filter crucible. Use
  additional acetic acid to transfer any remaining
  sample from test tube to crucible.

5

• Procedure (Cont)
• Apply vacuum to apparatus until all liquid passes
  through filter.
• Release vacuum momentarily, add about 2 mL
  additional acetic acid, and reapply vacuum.
• Repeat washing process twice with acetone.
• Dry sample under vacuum for a couple of minutes.
• Place crucible under heat lamp in hood until dry.
• Weigh crucible and contents
• Dry 10 minutes more and weigh again.
• Remove sample from crucible and weigh again on a
  pre-weighed watch glass.

6

• Calculations Protocol
• Applicable to All Experiments
• Set up equations showing variable names and
  relationships
• Show data substitutions
• Show appropriate units
• Report results to appropriate accuracy, i.e.
  correct number of significant figures and decimal
  places
• Set up equations and calculations in a neat, easy
  to read format

7

• Calculations
• Assumptions
• The photoreaction is complete
• All the ferric iron (Fe3) has been reduced to
  (Fe2)
• The mass of iron in the product must be the same
  as in the reactant
• Recall that you have weighed your Ferrous Oxalate
  Dihydrate product three times, with the final
  weight on the pre-weighed watch glass.
• mol wgt grams / moles
• moles grams / mol wgt
• mol wgt Fe(C2O4) ? 2H2O 179.90
• mol wgt K3Fe(C2O4)3 ? 3H2O 491.25
• mol wgt Fe
  55.85

8

• Record the 3 weight determinations on the Data
  Report form.
• Convert the product on the watch glass value to
  moles.
• Compute the theoretical weight of Fe2 in
  product
• Fe(C2O4) ? 2 H2O
• Compute the theoretical weight of Fe3 in
  reactant
• K3Fe(C2O4)3 ? 3H2O
• From the weight of iron in the Fe(C2O4) ? 2
  H2O(the product) and the mass of product
  produced experimentally, calculate the
  experimental mass of iron in the product.

9

1. Determine the experimental mass of iron (Fe3) in
   the reactant - Potassium Trioxalatoferrate
   Trihydrate.
2. Compute the experimental weight of iron (Fe3)
   in the reactant.
3. Compute the error for the theoretical and
   experimental values of the weight percent of
   (Fe3) in the Potassium Trioxalatoferrate
   Trihydrate complex.

10

• Compute the theoretical weight of Potassium in
  the reactant.
• Recall the experimentally determined weight
  percent values of the following in K3Fe(C2O4)3 ?
  3H2O
• Oxalate
• Water
• Iron
• Compute, by difference, the weight of Potassium
  in Potassium Trioxalatoferrate Trihydrate.