Processing kodak motion picture films, module 3 analytical procedures

Procedure
1. Weigh 6.0 g of sodium thiocyanate to the nearest
0.0001 g.
2. Quantitatively transfer to a 1000-mL volumetric flask
containing 100 mL reagent water. Swirl the flask to
dissolve the sodium thiocyanate.
3. Dilute to the mark with reagent water and stir to mix.
4. Pipet 50.0 mL of the sodium thiocyanate solution into
a 250-mL glass stoppered conical flask.
5. Pipet, while agitating, 50.0 mL of standardized 0.1 N
silver nitrate.
Calculations
% NaSCN = [(50.0 x N AgNO 3 ) – (mL x N NH 4 SCN)](81.07)(1000)(100)
(Sample wt (g))(50)(1000)
Where:
50.0 = mL of silver nitrate
N AgNO3 = normality of silver nitrate in meq/mL
mL = mL of NH4SCN titrated
N NH4SCN = normality of NH4SCN in meq/mL
81.07 = eq. wt. of NaSCN in mg/meq
50 = aliquot of sample taken
1000 = dilution volume in mL (in numerator)
100 = factor to convert to %
Sample wt = amount of sample weighed out in grams
1000 = factor to convert mg to g (in denominator)
Example:
% NaSCN = [(50.0 x 0.0991 N AgNO 3) – (13.2 x 0.0985 N NH 4SCN)](81.07)(1000)(100)
(6.0018)(50)(1000)
=
= 98.7%
[(4.955 – 1.3002)](81.07)(1000)(100)
(6.0018)(50)(1000)
To correct weighed amounts of sodium thiocyanate used to prepare standards:
(g of sodium thiocyanate reagent)(assay value determined)
(theoretical assay = 100%)
(0.6046 g of sodium thiocyanate reagent)(98.7)
100
= 0.5967 g of sodium thiocyanate corrected for assay
Caution
Observe safety precautions for handling concentrated
acids. Wear eye protection and impervious gloves. Use
caution and always add acid slowly to water.
Corrosive to skin, metals, and clothing. Avoid contact
with liquid and vapor. Use in an exhaust hood
6. Add 3 mL nitric acid and 2 mL ferric ammonium
sulfate indicator solution.
7. Titrate the excess silver nitrate with standardized
0.1 N ammonium thiocyanate solution. The end point
is the first permanent orange color that cannot be
removed upon stirring.
4 Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03