by Grace Neeson and Derek Brown

1. ANALYSIS AND USES
OF POTASSIUM
TRIS(OXALATO)FERR
GRACE NEESON AND DEREK
BROWN

2. DAY 1: PREPARATION OF K3[FE(OX)3].3H20
PROCEDURE
▸ Take a 250 mL beaker and fill it 2/3 full with
deionized water. Warm the water by heating it
on a hotplate; setting 3-4.
▸ Take a clean 100 mL beaker and dispense 25
mL of 0.8 mol/L oxalic acid, H2C2O4 (0.020mL)
into it.
▸ Weigh 5.0 g of ferrous ammonium sulphate,
FeSO4(NH4)2SO4.6H220 (0.013 mol), and add it
to the beaker containing the oxalic acid. Use a
glass rod to stir the solution to help the salt
dissolve.
▸ Take a small graduated cylinder and measure 1
mL of 1.0 mol/L H2SO4 (aq) from the dropper
bottle provided and add it to the oxalic acid
solution.

3. DAY 1: PREPARATION OF K3[FE(OX)3].3H20
PROCEDURE
▸ Use a graduated cylinder and measure
17 mL of deionized water and add it to
the oxalic acid solution.
▸ Heat the oxalic acid solution to boiling,
stirring constantly, then remove the
breaker from the heat source and allow
the yellow precipitate to settle.
▸ One settled, decant the clear solution
above the yellow precipitate.
▸ Was the yellow solid by adding warm
water and gently swirling the beaker.
Once again, allow the yellow solid to
settle and decant the clear liquid.

4. DAY 1: PREPARATION OF K3[FE(OX)3].3H20
PROCEDURE
▸ Weigh out 3.0 g of potassium oxalate,
K2C2O4.H2O (0.016 mol), and dissolve in 10 mL
of warm deionized water in a small beaker.
▸ Add the potassium oxalate solution to the
beaker containing the yellow solid. Add a
magnetic stir bar.
▸ At the sink, charge a clean burette with 15 mL
of 0.88 mol/L hydrogen peroxide solution, H2O2
(aq), and secure it to a burette clamp on a ring
stand.
▸ Transfer the beaker containing the yellow sold
and potassium oxalate to a hotplate and warm it
(setting 3) while stirring gently using the
magnetic stirrer.

5. DAY 1: PREPARATION OF K3[FE(OX)3].3H20
PROCEDURE
▸ Dispense 8.5 mL of the 0.88 mol/L hydrogen
peroxide solution from the burette into the
beaker while continuing to stir.
▸ Heat the mixture to near boiling.
▸ Dispense 10 mL of the 0.8 mol/L oxalic acid
(0.0056 mol) solution into a transfer beaker
and then add nearly boiling solution.
▸ Add a further 1.5 mL of the 0.88 mol/L H2O2
(aq) solution from the burette into the nearly
boiling solution.
▸ At this stage you should have a clear green
solution, but if the solution contains solid
material you will need to filter it.

6. DAY 1: PREPARATION OF K3[FE(OX)3].3H20
PROCEDURE
▸ Cool the solution and then add 10 mL
of the ethanol gradually to the beaker,
while swirling.
▸ Place the beaker in your glassware
drawer for 15 minutes.
▸ Once crystallization is complete, filter
the crystals on the filter pas with
portions of 50/50 ethanol/water
mixture, and give a final rinse with
acetone. Then draw air through the
filter pas until it is completely dry.

7. DAY 1: PREPARATION OF K3[FE(OX)3].3H20TEXT
PROCEDURE
▸ Carefully transfer the crystals to a
weighing paper and weigh the
crystals to obtain a yield.
▸ Transfer the crystals to a clearly
labelled glass vial.
▸ Wrap the vial in aluminium foil and
place it onto the storage tray
provided.

8. DAY 2: ANALYSIS AND USES OF OF K3[FE(OX)3].3H20
PROCEDURE 1
▸ Weigh out threw separate samples of the
complex on an analytical balance. Each
sample should be close to 0.1600 g;
record the actual value to four decimal
places.
▸ Transfer each sample to a separate
Erlenmeyer flask and add 10 mL of 5.0
mol/L H2SO4.
▸ Warm the mixture to 60˚C. When the solid
has dissolved, titrate the solution with
standardized potassium permanganate
until the first permanent trace of pink is
seen in the flask.

9. DAY 2: ANALYSIS AND USES OF OF K3[FE(OX)3].3H20
Sample #
Burette
Reading
Initial (mL)
Burette
Reading
Final (mL)
Volume
KMnO4
Used (mL)
Volume
KMnO4
Used (L)
Accuracy
Ratio
Mols
KMnO4
used
Calculated
Grams of
complex
1 6.00 32.40 26.40 0.02640 0.1641 3.978 x 10-
4 0.1629
2 7.85 33.50 25.65 0.02565 0.1608 3.865 x 10-
4 0.1582
3 8.25 34.20 25.95 0.02595 0.1623 3.911 x 10-
4 0.1601
TITRATION
TABLE

10. DAY 2: ANALYSIS AND USES OF OF K3[FE(OX)3].3H20
PROCEDURE 2
▸ Transfer 0.737g of the complex to a 250 mL
volumetric flask containing 100 mL of water and 25
mL of 1.0 mol/L H2SO4. Make up to the mark with
water, stopper, mix thoroughly and store in a dark
cupboard.
▸ Pipette 10 mL of the actinometer solution into each
of two 50 mL volumetric flasks. Place one flask on
the overhead projector. Place the other flask in a
dark place. After 5 minutes remove the flask and
add the developers (1 ML 0.1% w/v bipyridine and
8 mL 10 % w/v sodium acetate). Make up the to
mark with distilled water and shake thoroughly.
Record the absorbance of the solution as 512 nm
using the solution which has been kept in the dark
as a blank. Measure the absorbance of the
solution which was kept in the light.
The flask that had
been on the overhead.
The flask that had
been in the dark.

11. DAY 2: ANALYSIS AND USES OF OF K3[FE(OX)3].3H20
TITRATION ACCURACY RATIO
▸= (highest ratio - lowest ratio) / (average ratio) x100%
▸= (0.1623 - 0.1608) / ((0.1623 + 0.1608)/ 2) x100%
▸= 0.9285%
PHOTONS ABSORBED / SECOND
▸time on overhead projector = 324 s
▸absorbance at 512 nm = 0.35
▸A = εbc
▸c (mol/L) = absorbance / 7.0x103 (mol/L-cm)
▸c = 0.35 / 7.0x103
▸c = 5.0x10-5 mol/L
▸Fe2+ mol = c / volume of solution
▸Fe2+ mol = 5.0x10-5 mol/L x 0.050 L
▸Fe2+ mol = 2.5x10-6 mol
▸photons absorbed per second = 2.5x10-6
mol x 6.02x1023 mol-1 / 324 s
▸photons absorbed per second = 4.7x1015

12. DAY 2: ANALYSIS AND USES OF OF K3[FE(OX)3].3H20
LIMITING
REACTANT▸ moles of K+ ions
▸ = 0.016 mol K2C2O4.H2O x 2
▸ = 0.032 mol / 3 mol
▸ = 0.0107 mol
▸ smallest value, therefore the
limiting reagent
THEORETICAL YIELD
▸= 0.0107 mol K2C2O4.H2O x 491.25
g/mol
▸= 5.2 g
▸= (actual weight / theoretical weight)x100%
▸= (3.5525 g / 5.2 g)x100%
▸= 68%
PERCENT
YIELD
▸ moles of Fe3+ ions
▸ = 0.013 mol
FeSO4(NH4)2SO4.6H220
▸ = 0.013 mol / 1 mol
▸ = 0.013 mol
▸ moles of ox- ions
▸ = 0.016 mol K2C2O4.H2O +
0.0056 mol oxalic acid + 0.020 ml
oxalic acid
▸ = 0.0216 mol / 3 mol
▸ = 0.014 mol

13. DAY 2: ANALYSIS AND USES OF OF K3[FE(OX)3].3H20
PERCENT PURITY
▸ mol KMnO
▸ = mol/L KMnO4 x titration volume
▸ = 0.0150 mol/L KMnO4 x 0.02580 L
▸ = 3.888x10-4 mol KMnO4
▸ mol complex
▸ = mol KMnO4 x 1 mol complex / 1.2 mol
KMnO4
▸ = 3.888x10-4 mol KMnO4 x 1 mol complex /
1.2 mol KMnO4
▸ = 3.240x10-4 mol complex
▸grams of complex
▸= mol complex x molar mass/mol
▸= 3.240x10-4 mol complex x 491.25g/mol
▸= 0.1592 g complex
▸average mass of samples weighed out
▸= (0.1595 g + 0.1599 g)/2
▸= 0.1597 g
▸percent purity
▸= (average grams of complex calculated /
average mass of samples weighed out) x
100%
▸= (0.1592 / 0.1597) x 100%
▸= 99.69%

14. DAY 2; ANALYSIS AND USES OF OF K3[FE(OX)3].3H20
SOURCES OF ERROR
▸Percent Yield:
▸Lost some crystals in the filtration process
▸Didn’t allow the crystals enough time to crystallize
▸Percent Purity:
▸Drops getting stuck to the side of the beaker, thus
decreasing the number of moles that reach the solution,
and therefore increasing molarity