CALCULATIONS
For Potentiometric Titration
A. Hypo Index (HI) or Total Reductants:
(mL Blank A – mL Sample A) (N Na2S2O3)
HI (1), mL =
0.1000 N Na2S2O3
Where:
HI (1), mL = mL of 0.1000 N I2 consumed by 1.0 mL sample
mL Blank A = millilitres of titrant at the end point of the blank titration of potentiometric Procedure A.
mL Sample A = millilitres of titrant at the end point of the sample titration of potentiometric Procedure A.
N Na2S2O3 = normality of the titrant (meq/mL)
0.1000 = nominal value for the normality of the titrant, in meq/mL
B. Thiosulfate (S2O3=):
(mL Blank B – mL Sample B)(N Na2S2O3)(112.13)(1000)
g/L S2O3= =
sample size (1000)
Where:
mL Blank B = millilitres of titrant at the end point of the blank titration of potentiometric Procedure B
mL Sample B = millilitres of titrant at the end point of the sample titration of potentiometric Procedure B.
N Na2S2O3 = normality of the titrant (meq/mL)
112.13= equivalent weight of thiosulfate expressed in mg/meq
1000 = conversion factor of milligrams to grams
1000 = conversion factor of millilitres to litres
sample size = sample size used in potentiometric Procedure B (2.0 mL)
C. Sodium Sulfite (Na2SO3):
mL Blank A – mL Sample A = D mL A
mL Blank B – mL Sample B = D mL B
[(D mL A)(2.0) – (D mL B)](N Na2S2O3)(63.02)(1000)
g/L Na2SO3 =
sample size (1000)
Where:
N Na2S2O3 = normality of the titrant
2.0= conversion of hypo index to 2.0 mL sample size
63.02= equivalent weight of sodium sulfite in mg/ meq
1000 = conversion factor of milligrams to grams
sample size = sample size used in potentiometric Procedure B (2.0 mL)
1000 = conversion factor of millilitres to litres
8 | Processing KODAK Motion Picture Films, Module 3, Analytical Procedures • H24.03 |