Processing kodak motion picture films, module 3 analytical procedures

The theoretical concentration of iron (II) is calculated in the
fourth step.
4) Theoretical wt of Iron (II) in Solution
g/L iron (II) =
Where:
Finally, the assay percentage of the ferrous ammonium
sulfate hexahydrate is determined using the actual iron
concentration (determined in step 3) and the theoretical iron
concentration (determined in step 4) as follows:
5) Assay Percentage
Alternate Assay Procedure for Ferrous Ammonium
Sulfate, Hexahydrate
Note: This procedure is based on the method in Reagent
Chemicals, 8th Edition, Amercian Chemical Society, 1993.
Assay Procedure
Note: This procedure should be repeated in triplicate with
the average of the three results used as the assay value.
1. Accurately weigh 1.6 grams of sample to the nearest
milligram and dissolve in a mixture of 100 mL reagent
water and 3 mL of concentrated sulfuric acid
contained in a 250 mL Erlenmeyer flask.
Caution
Always add acid to water and not water to acid.
2. Titrate while stirring with standardized 0.1 N
potassium permanganate (KMnO4 ) from a 50 mL
buret to a permanent faint pink endpoint that lasts for
at least 15 seconds.
3. Repeat steps 1 and 2 without any sample. This is the
blank.
Calculations
wt of Fe(NH4) 2(SO4) 2 6H2O 55.85 1000 mL
x x
200 mL 392.13 1 L
wt of Fe(NH4 ) 2 (SO4 ) 2 6H2O = weight (g) recorded in Step 1
55.85 = atomic weight of iron (g/mole)
1000 mL = factor to convert mL to Litre
200 mL = preparation volume for
Fe(NH4 ) 2 (SO4 ) 2 6H2O 392.13 = molecular weight (g/mole) of
ferrous ammonium sulfate,
6-hydrate
% iron (II) = g/L iron (II) (actual) x 100
g/L iron (II) (Theo.)
% (wt./wt.) ferrous ammonium sulfate, hexahydrate =
(mL KMnO4 sample - mL KMnO4 blank) x N KMnO4 x 0.3921 x 100
sample size in grams
6 Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03