Processing kodak motion picture films, module 3 analytical procedures

APPENDIX B
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, K2Cr2O7 , NIST Primary
Standard, 136e, dried for 2 hours at 110°C
Ferroin Indicator, 1,10-Phenanthroline Iron(II) Sulfate
solution (0.025 M) [(C 12 H 8 N 2 ) 3 FeSO 4 ]
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,
hexahydrate to the nearest 0.0001 g and record the
weight.
2. Quantitatively transfer to a 200-mL volumetric flask
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 reagent water and a
magnetic stirring bar.
Caution
Hot acid solution is formed.
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 that
produced the first reddish-brown color change is the
end point.
12. Record the volume of ferrous ammonium sulfate
titrant consumed at the end point to the nearest
0.05 mL.
13. Repeat steps 7-12, two more times.
Calculations
N Potassium Dichromate
where:
N K 2 Cr 2 O 7 =
N of Ferrous Ammonium Sulfate
N Fe(NH4 ) 2 (SO4 ) 2
where:
= (mL K2Cr2O7 )(N K2Cr2O7 )
mL Fe(NH4) 2(SO4) 2
g/L, Iron(II) in Ferrous Ammonium Sulfate
g/L, Iron(II) (actual)
where:
= N Fe(NH4 ) 2 (SO4 ) 2 x 55.85
Theoretical wt of Ferrous in Solution
Assay Percentage
g wt of K2Cr2O7 1000
x
100 mL 294.2/6
294.2/6 = the eq. wt of K2Cr2O7 g wt of K2Cr2O7 = recorded wt from step 4
1000 = factor to convert equivalents to
milliequivalents
mL Fe(NH4 ) 2 (SO4 ) 2 =average * volume of the three titrations
required to reach the end point color
change
mL K2Cr2O7 = 15.0 mL
N K2Cr2O7 = normality calculated in N Potassium
Dichromate
* The average volume for the three titrations should not have a standard
deviation (1s) greater than 0.50 mL.
55.85 =
gram-equivalent weight of Iron(II) in
Fe(NH 4) 2(SO 4) 2 6H 2O
g/L
iron(II)
where:
= wt of Fe(NH4 ) 2 (SO4 ) 2 6H2O x 55.85 200 mL 391.85
1000 mL
x
1L
391.85 = molecular weight of ferrous
ammonium sulfate, 6-hydrate
55.85 = atomic weight of iron
wt of Fe(NH4 ) 2 (SO4 ) 2 6H2O = weight recorded in step 1 of
this procedure.
1000 mL = factor to convert mL to L
%Iron(II) =
g/L Iron(II) (actual)
g/L Iron(II) (theoretical)
x 100
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 5