Processing kodak motion picture films, module 3 analytical procedures

APPENDIX II
This appendix contains two assay procedures for Ferrous
Ammonium Sulfate. The first procedure uses Potassium
Dichromate; while the alternate procedure uses Potassium
Permanganate titrant.
Assay Procedure for Ferrous Ammonium Sulfate,
Hexahydrate
Reagents
All reagents are ACS Reagent Grade unless otherwise stated.
Potassium Dichromate, K 2 Cr 2 O 7 ,
NIST Primary Standard, 136e, dried for 2 hours at 110°C
Ferroin Indicator, 1,10 Phenanthroline ferrous sulfate
(0.025 M)
Sulfuric Acid, concentrated, H 2 SO 4
Ferrous Ammonium Sulfate 6-Hydrate,
Fe(NH 4 ) 2 (SO 4 ) 2 6H 2 O
Procedure
1. Weigh 14.0 g of ferrous ammonium sulfate to the
nearest 0.0001 g and record the weight.
2. Quantitatively transfer to a 200-mL volumetric flask
with reagent water and swirl the flask to dissolve the
ferrous ammonium sulfate.
3. Dilute the solution to the mark with reagent water.
Invert the flask, 6-10 times, to thoroughly mix.
4. Weigh 1.0 g of dried, potassium dichromate to the
nearest 0.0001 g and record the weight.
5. Quantitatively transfer to a 100-mL volumetric flask
containing 50 mL of reagent water. Swirl the flask to
dissolve the potassium dichromate.
6. Dilute the solution to the mark with reagent water.
Invert the flask 6-10 times, to mix thoroughly.
7. Fill a 50-mL buret with the ferrous ammonium sulfate
solution (step 3, above).
8. Add 20 mL concentrated sulfuric acid to a 150-mL
beaker containing 25 mL of distilled water and a
magnetic stirring bar.
Caution
Hot acid solution is formed. Always add acid to water
and not the converse
9. Pipet 15.0 mL of the potassium dichromate solution
into the beaker.
10. Add 2 drops of ferroin indicator to the beaker and
place the beaker on a magnetic stirrer.
11. Slowly add the ferrous ammonium sulfate solution
from the buret to the beaker. The solution will change
colors as the titrant is added, going from a green-blue
color to a reddish-brown color. The point the produces
the first reddish-brown color change is the end point.
12. Record the volume of the ferrous ammonium sulfate
titrant consumed to the nearest 0.05 mL at the end
point.
13. Repeat steps 7–12, two more times.
Calculations
To calculate the Assay Percentage, four preliminary
calculations must first be performed. first, the normality of
the potassium dichromate must be determined.
1) N Potassium Dichromate
N K 2 Cr 2 O 7 = gwtofNK 2 Cr 2 O 7 x1000
100 x 49.03
Where:
g wt of K2Cr2O7 = recorded weight from step 4
1000 = factor to convert equivalent wt. to
milliequivalent wt.
100 = volume of K2Cr2O7 solution in mL
49.03 = g/equivalent wt. of K2Cr2O7 Once the normality of the potassium dichromate is known,
the value is used in the second calculation to determine the
normality of the ferrous ammonium sulfate.
2) N of Ferrous Ammonium Sulfate
N Fe(NH 4) 2(SO 4) 2 6H 2O =
Where:
Once the normality of the ferrous ammonium sulfate has
been calculated, it is used to determine the actual iron (II)
concentration in g/L in the third calculation.
3) g/L, Iron (II) in Ferrous Ammonium Sulfate
Where:
(mL K2Cr2O7 )(N K2Cr2O7 )
mL Fe(NH4 ) 2 (SO4 ) 2 6H2O mL K2Cr2O7 = 15.0 mL volume of K2Cr2O7 solution taken
N K2Cr2O7 = Normality (meq./mL)
calculated, above
mL Fe(NH4 ) 2 (SO4 ) 2 6H2O = average volume * of the three
titrations required to reach
the end point color change.
* The average volume for the three titrations should not have a standard
deviation (1 s) greater than 0.50 mL
g/L, Iron (II) (actual) = N Fe(NH 4) 2(SO 4) 2 6H 2O x 55.85
55.85 =
equivalent weight (g/equivalent) of Iron (II) in
Fe(NH 4 ) 2 (SO 4 ) 2 6H 2 O
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 5