HIRANUMA APPLICATION DATA

Factorstandardization

Automatic Titrator

Data No.

O3

Feb. 03,2022

Standardization of sodium thiosulfate titrant

1. Abstract
Sodium thiosulfate standard solution is used as a titrant for iodometric titration method. In iodometrictitration, an equivalent amount of iodine (I2) is produced by reacting the oxidant component in measurement
sample with the added potassium iodide (KI). The generated iodine (I2) is titrated with sodium thiosulfate
standard solution, which enables the titration of the oxidant component indirectly.
Factors are indicated on the commercially available standard solution for volumetric analysis. The factor
determination is required when the standard solutions are prepared in the laboratory. Also it is effective tocheck the repeatability by the factor measurement using a standard material to check the performance of titrator
system. Japanese Industrial Standard JIS K 8001 and the Japanese Pharmacopoeia describe that potassiumiodate (KIO3), which is a standard material for a volumetric analysis, should be used for the factor
determination of sodium thiosulfate standard solution.
The measurement procedure is as follows. The potassium iodate (KIO3) standard solution is taken into an
Erlenmeyer flask with a stopper by volumetric pipet, add sulfuric acid to acidify the solution, and then add
potassium iodide (KI) to it. Promptly the stopper is attached on the flask and left to stand for 10 minutes,
equivalent amounts of iodine (I2) to potassium iodate (KIO3) are produced according to equation (1). The factor
is determined by performing potentiometric titration of this iodine (I2) with sodium thiosulfate standard
solution according to equation (2). 6 mol of sodium thiosulfate indirectly reacts quantitatively with 1 mol ofpotassium iodate (KIO3), and the titration curve shows an inflection point at the end point.
KIO3 ＋ 5KI + 3H2SO4 → 3I2 + 3K2SO4 + 3H2O･･･(1)

2Na2S2O3 + I2 → Na2S4O6 + 2NaI･･･(2)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: Automatic Titrator

COM SeriesElectrodes: Platinum-reference combination electrode (long type)PR-733BZStirrer: In order to attach a long-type electrode compatible with the Erlenmeyer flask,
it is necessary to add or change some parts of the stirrer, as explained in section
5. (3).

(2) Reagents
Titrant: 0.1 mol/L (0.1 N)*1 sodium thiosulfate standard solution (Buret No. 1)

Standard material : 1/60 mol/L (0.1 N)*1 Potassium iodate (KIO3) standard solution (f = 1.003)
Prepared by dissolving standard material for volumetric analysis(Certified value of purity for the standard material in this report: 99.97 %)Additive reagent: Diluted sulfuric acid solution (Approx. 16 %)Prepared by slowly adding 10 mL of sulfuric acid to 90 mL of DI water.
Potassium iodide (KI)

*1: Regarding the normality (N) of the concentration unit, it is explained in section 5. (2).

3. Measurement procedure(1) Take 10 mL of 1/60 mol/L potassium iodate (KIO3) standard solution into a 200 mL Erlenmeyer flaskwith volumetric pipet.
(2) Add 25 mL of DI water, 10 mL of diluted sulfuric acid solution and a stirrer bar to the flask. Swirl theflask gently.
(3) Add 2 g of potassium iodide (KI) into the flask and promptly attach a stopper on the flask. Swirl theflask gently.
(4) Leave to stand for 10 minutes.
(5) Add 100 mL of DI water to the flask.
(6) Immerse the electrode and start the measurement. Titration is performed with 0.1 mol/L sodium
thiosulfate standard solution, and the inflection point on the titration curve is detected as the end point.
(7) Perform the blank test with the same procedure of sample measurement.

4. Measurement conditions and results
Examples of titration conditions
Blank measurement

Cndt No.
1MethodAuto
ConstantNo.
1Mode No.
18 *2Buret No.
1Size0 g
Pre Int0 sec
Amp No.
1Blank0 mL
Del K0D. UnitmVMolarity
0.1 N
Del Sens
0 mV
S-Timer
5 sec
Factor0Int Time
3 sec
C.P. mL
0 mL
K0Int Sens
3 mV
T Timer
0 sec
L0Brt Speed
2
D.P. mL
0 mL
Pulse
40
End Sens
300
Unit
mL
Over mL
0.5 mL
FormulaD
Max.Vol.
1 mL
Digits3*2: Since the maximum change in electrode potential is shown at the first or the second drop of this blanktitration, no clear inflection point appears on the titration curve. To detect this maximum change as an end point,
set Mode No. to which the blank mode function is assigned, Mode No.12-19 for COM-A19.

Factor standardization measurement with potassium iodate (KIO3)

Cndt No.
2Method
AutoConstantNo.
2Buret No.
1Size
10 mL
Amp No.
1Blank
0.076 mL
D. UnitmV
Molarity
0.1 N
S-Timer
5 sec
Factor
1.003 *3
C.P. mL
0 mL
K0T Timer
0 sec
L0D.P. mL
1.0 mLEnd Sens300Unit
Fact1
Over mL
0.5 mL
FormulaS/(D-B)*F
Max.Vol.
20 mL
Digits4*3: Factor of 1/60 mol/L potassium iodate (KIO3) standard solution

Mode No.
Pre Int
Del K
Del Sens
Int TimeInt Sens
Brt Speed
Pulse

50
503
3240

secmV
sec
mV

Measurement results
Measurement results of factor standardization

Measurement
No.

Samplesize (mL)-Potassium iodate

12
1standard solution

210

SampleBlank

3Blank measurement

Titrant
volume(mL)
0.074
0.078
10.16510.176
10.172

FactorStatistical results

0.9942Avg.

0.076 mL

Avg.
SDRSD

0.9940.001
0.06 %

0.9931
0.9935

Factor standardization measurement

Examples of titration curves

5. Note(1) About a sampling of the standard material
Potassium iodate (KIO3) is used for the standardization of sodium thiosulfate standard solution in redox
titration. The standard material for volumetric analysis comes with a certificate value of the purity anduncertainty. If the certification and traceability are required for the management of test result, such as quality
records, the standard material for volumetric analysis is used. It is necessary to prepare the standard materialwith pretreatment such as drying as described in its instruction before use.
In this report, the standard solution prepared from solid of potassium iodate (KIO3), which is a standard
material for volumetric analysis, is used as the standard sample. Otherwise, solid potassium iodate (KIO3) canbe directly used as the standard sample for this titration. However, in that case, the potassium iodate (KIO 3)
should be weighed accurately in small amounts as about 50 mg or less estimated from the reaction ratio shownin the following formula (3).
･･･(3)

1 mL of 0.1 mol/L sodium thiosulfate = 3.567 mg of potassium iodate (KIO3)(2) Concentration of potassium iodate (KIO3) standard solution to prepare

When a standard solution is used as the standard sample for factor standardization, the concentration ofstandard sample and titrant should be the same concentration in a normality (N) unit. The normality ofconcentration unit is indicated by the value obtained by multiplying the molar concentration by the valence ofits chemical species. The valence in redox titration means how many mol of electrons are transferred by 1 molof oxidant (or reductant). The normality (N) and valence of the reagents used in this report are as follows.
Sodium thiosulfate：0.1 mol/L = 0.1 N, (Valence: 1)

Potassium iodate (KIO3)：1/60 mol/L = 0.1 N, (Valence: 6)

When a standard solution is used as the standard sample, the formula (Fact1) for calculating the factor of thetitrant is indicated by [S / (DB)×F]. This is derived from the following relational equation (4). The left side(subscript “s”) indicates the standard sample, and the right side (subscript “t”) indicates the titrant.

ns × Ms ×Fs × S = nt × Mt × Ft × (D  B)
Standard solution・・・(4)Titrant

ns：Valence

nt：Valence

Ms：Molarity

Mt：Molarity

Fs：Factor (Known)

Ft：Factor (Unknown)

S：Sample size (mL)

D-B

：Titrant volume at end point (mL)

If the standard sample and the titrant have the same normality (N), the product of valence and molarity on theright and left sides will be equal as [ns × Ms = nt × Mt], and this term can be omitted from equation (4). By
converting equation (4) into a form that finds an unknown “Ft”, the equation [S / (DB) × F] of “Fact1” isobtained. For this reason, when “Fact1” is selected for the calculation formula, it is necessary to prepare thestandard sample and the titrant with the same concentration in normality (N).

(3) About electrodes and stirrers that fit in Erlenmeyer flasks
In this report, since a 200 mL Erlenmeyer flask is used as a titration vessel, platinum-reference combinationelectrode PR-733BZ (Long type) was used. The stirrer is modified to accommodate Erlenmeyer flasks asshown in Fig. 1 to attach the long type electrode. The figure below is a modification example of the Stirrer
K-3000T attached to the titrator COM-A19.

Figure 1 A set of electrode and stirrer parts for Erlenmeyer flasks

(4) How to check the performance of the titrator with sodium thiosulfate titrant without using an Erlenmeyer
flask
In this report, an Erlenmeyer flask with a stopper is used as the titration vessel in order to titrate iodine (I2)
generated from equivalent amount of potassium iodate (KIO3), which is a standard substance for volumetricanalysis. For this reason, it is necessary to replace or add parts for the electrodes and stirrer as shown in section
5. (3).
If purpose of the measurement is not to determine the factor of sodium thiosulfate and just to check theperformance of a titrator system (device, electrode, sodium thiosulfate standard solution), it is able to use
iodine (I2) standard solution as the standard sample. In that case, a beaker can be used as the titration vessel.
The electrodes that can be used are not limited to the long and combination type, and can also be used with thehalf-cell type, such as PT-301 and RE-201Z.
However, since the iodine (I2) standard solution is inferior in stability to potassium iodate (KIO3), it is notrecommended to use it for factor determination of sodium thiosulfate. Otherwise, it can be used for theperformance check of the titrator system based on repeatability. Details are described in Application Data No.
O7.

Keywords：Factor standardization, Redox titration, Sodium thiosulfate, Potassium iodate※Depend on the configuration of instrument, ,some of measurement may not possible