HIRANUMA APPLICATION DATA

Factorstandardization

Data No.

Automatic Titrator

O7Feb. 03,
2022

Standardization of iodine titrant

1. Abstract
Iodine (I2) is an oxidant and its redox pair is an iodide ion(I-). In the iodometric titration method, anexcessive amount of iodide ion(I-) is reacted with the oxidizing agent in the sample. The produced iodine(I2) istitrated with sodium thiosulfate and the oxidant is indirectly quantified. This method is widely used to quantifyoxidants. On the other hand, in the iodimetric titration method, the reducing agent in the sample is directly
titrated with an iodine(I 2) titrant: example of its use is the quantification of sulfites.
Since iodine(I2) is volatile, it is necessary to check the factor of the iodine standard solution before use asa titrant. JIS K8001 and the Japanese Pharmacopoeia describe that the sodium thiosulfate standard solution
should be used for factor standardization of the iodine(I2) standard solution. 2 mol of sodium thiosulfate reacts
quantitatively with 1 mol of iodine(I2) by equation (1) and shows an inflection point on the titration curve.
2Na2S2O3 + I2 → Na2S4O6 + 2NaI･･･(1)1) Japanese Pharmacopoeia Eighteenth Edition
2) Japanese Industrial Standard JIS K8001 General rules for test methods of reagents

2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit
Electrodes: Automatic Titrator

COM Series

Optional buret

1 unit: Platinum electrodePT-301

Reference electrodeRE-201Z* It can also be applied to combinations of other platinum electrodes such as
PR-701BZ.
(2) ReagentsStandard material : 0.1 mol/L (0.1 N) sodium thiosulfate standard solution (f = 1.000, Buret No. 1),
Used as a titrant
Sample to be standardized: 0.05 mol/L (0.1 N) iodine(I2) standard solution (Buret No.2), Used as a sample

3. Measurement procedure(1) Add 50 mL of DI water and a stirrer bar to a 100 mL beaker.
(2) Immerse the electrodes and start the measurement. 10 mL of 0.05 mol/L iodine(I2) standard solution isadded to the beaker by the buret dispensing.
(3) Titration is subsequently performed with 0.1 mol/L sodium thiosulfate standard solution. The inflection
point on the titration curve is detected as the end point.

4. Measurement conditions and results
Examples of titration conditions
Factor standardization measurement of 0.05 mol/L iodine(I2) standard solution

M. File1+2Cndt No.
1Method
DispBuret No.
2S-Timer
5 sec
Disp Vol.
10 mL
Cndt No.
2
MethodAutoConstantNo.
2Buret No.
1Size
10 mL
Amp No.
2Blank0 mL
D. UnitmV
Molarity
0.1 mol/L
S-Timer
5 sec
Factor1.000 *1
C.P. mL
0 mL
K0T Timer
0 sec
L0D.P. mL
0 mL
End Sens
1000
Unit
Fact(D-B)/S*F
Over mL
0.3 mLFormula
Max.Vol.
20 mL
Digits4*1: Factor of 0.1 mol/L sodium thiosulfate standard solution

Mode No.
Pre IntDel KDel Sens
Int TimeInt Sens
Brt SpeedPulse

40903
3
240

Measurement results
MeasurementNo.
1
2
3Samplesize (mL)
1010
10Titrant
volume (mL)
10.03110.03610.035

Factor
1.00311.00361.0035

Statistic calculation
Avg. 1.003
0.0003SD0.03 %RSDsecmVsecmVMeasurement of factor of iodine standard solution

Examples of titration curves

5. Note(1) About the factor calculation formula of the iodine(I2) standard solution
In measurement of the factor standardization, there are many case examples of titrating a standard materialusing the titrant to be standardized. In the procedure of JIS K8001 and Japanese Pharmacopoeia for iodine(I2)standard solution, the titrant and the sample are reversed. The sodium thiosulfate standard solution is used as
the titrant, and the iodine(I2) standard solution to be standardized is used as the sample for titration.
In this case, the factor calculation formula is set as [(D-B)/S*F]. This formula is not initially installed in thetitrator and must be set using the formula editing function.
The calculation formula is derived based on the following relational formula (2). The left side (subscript s) isthe titrant of sodium thiosulfate standard solution and has already been standardized preliminary, and the rightside (subscript t) is the sample of iodine(I2) standard solution to be standardized.
ns × Ms ×Fs × (D - B) = nt × Mt × Ft × S
Sodium thiosulfate・・・(2)Iodine(I2)

ns：Valence (1)nt：Valence (2)Ms：Molar concentration (0.1)

Mt：Molar concentration (0.05)

Fs：Factor (Known)

Ft：Factor (Unknown)

D-B：Titrant volume (mL)

S：Sample size (mL)

Keywords：Factor standardization, Redox titration, Iodine, Sodium thiosulfate*Some measurement would not be possible depending on optional configuration of system.