Processing kodak motion picture films, module 3 analytical procedures

Iodometric Determination of Ferricyanide in Ferricyanide Bleach
ECR-1100G
Process ECN-2 ECP-2D VNF-1/LC RVNP
Formulas — — SR-40 —
PRINCIPLE
Excess iodide ions and a zinc reagent are added to the bleach
sample. The ferricyanide reacts with the iodide to produce an
equivalent amount of iodine. The iodine is titrated with
standard sodium thiosulfate. The reaction of ferricyanide and
iodide is quantitative as long as zinc ions are present in
excess. Any ferrocyanide present in the bleach, as well as the
ferrocyanide produced by the reduction of ferricyanide, is
precipitated as zinc ferrocyanide. Carbowax is not separated
out of the sample in this method, and if present in your
solution, may interfere with the iodine end point.
Persulfate ions and some other oxidizing agents will also
oxidize iodide. Thus, if present, they will be measured as
ferricyanide by this method.
This method requires handling potentially hazardous
chemicals. Consult the Material Safety Data Sheet for each
chemical before use. MSDS's are available from your
chemical supplier.
Note: Use pipets and volumetric glassware meeting the
“Class A” definition by the National Institute of Standards
and Technology (NIST).
REAGENTS
Use ACS Reagent Grade reagents unless specified
otherwise.
0.60 M Potassium iodide, KI
Zinc Sulfate/7.0 N Sulfuric Acid Reagent
0.1 N Sodium Thiosulfate, Na 2 S 2 O 3
(standardized to 4 decimal places)
Starch Indicator
PROCEDURE
Removal of Interfering Constituents
1. Pipet (wipe the pipet before leveling) the indicated
sample size into a 250-mL conical flask.
2. Add 25 mL of 0.60 M potassium iodide from a tip-up
pipet.
3. Add 20 mL of zinc sulfate/7.0 N sulfuric acid reagent
from a tip-up pipet; mix thoroughly.
Titration
1. Titrate with standardized 0.1 N sodium thiosulfate to a
light yellow color.
2. Add 5 mL of starch indicator from a tip-up pipes, and
continue the titration until the blue color just
disappears.
Calculations
VNF-1/LC (5-mL sample)
K 3 Fe(CN) 6 , g/L =
Process Sample Size
VNF-1/LC 5.00 mL
(N Na 2S 2O 3)(mL Na 2S 2O 3)[eq wt K 3Fe(CN) 6](1000)
Na 3 Fe(CN) 6 , g/L =
(mL sample)(1000)
(N Na 2 S 2 O 3 )(mL Na 2 S 2 O 3 )(329.25)(1000) =
(5.00)(1000)
65.85(N Na 2 S 2 0 3 )(mL Na 2 S 2 O 3 )
(N Na 2 S 2 O 3 )(mL Na 2 S 2 O 3 )[eq wt Na 3 Fe(CN) 6 ](1000) =
(mL sample)(1000)
(N Na 2 S 2 O 3 )(mL Na 2 S 2 O 3 )(280.92)(1000) =
(5.00)(1000)
56.18(N Na 2S 20 3)(mL Na 2S 2O 3)
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1
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