HIRANUMA APPLICATION DATA

Factorstandardization

Automatic Titrator

Data No.

O1Feb. 03,
2022

Standardization of hydrochloric acid titrant

1. Abstract
The measurement method of alkaline substance by neutralization titration using a hydrochloric acidstandard solution is widely used in the titration analysis. Factors are indicated on the commercially available
standard solution for volumetric analysis. The factor determination is required when the standard solutions areprepared in the laboratory. Also it is effective to check the repeatability by the factor measurement using astandard material to check the performance of titrator system. Japanese Industrial Standard JIS K 8001 and theJapanese Pharmacopoeia describe that sodium carbonate, which is a standard material for a volumetricanalysis, should be used for the factor determination of hydrochloric acid standard solution.
In this report, sodium carbonate, which is a standard material, was dissolved in pure water, andpotentiometric titration was performed with 0.1 mol/L hydrochloric acid standard solution to determine thefactor. 1 mol of sodium carbonate and 2 mol of hydrochloric acid react quantitatively according to Eq. (1) and(2), and the titration curve shows two inflection points. The first and second inflection points appear at thealkaline pH and the acidic pH, respectively. In this report, the end point of the titration is defined as theequivalent point in Eq. (2), thus the second inflection point is detected as the end point.
Na2CO3 ＋ HCl → NaHCO3 ＋ NaCl･･･(1)

NaHCO3 ＋ HCl → NaCl ＋ CO2 ＋ H2O･･･(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: Glass electrodeGE-101B

Reference electrodeRE-201Z(2) Reagents
Titrant: 0.1 mol/L (0.1 N) hydrochloric acid standard solution (Buret No. 1)

Standard material : Sodium carbonate, standard material for volumetric analysis(Certified value of purity in this report: 100.00 %)3. Measurement procedure(1) Take about 0.15 g of sodium carbonate into a 100 mL beaker and weigh it accurately to 0.1 mg digits.
(2) Add 50 mL of DI water and a stirrer bar to the 100 mL beaker to dissolve the sample.
(3) Immerse the electrodes and start the measurement. Titration is performed with a 0.1 mol/Lhydrochloric acid standard solution, and the second inflection point on the titration curve is detected asthe end point. The parameter setting which does not detect the first inflection point is explained inSection 5.
(4) Perform the blank test with the same procedure of sample measurement.

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

Cndt No.
1
MethodAutoConstantNo.
1Mode No.
16 *1
Buret No.
1Size0 g
Pre Int0 sec
Amp No.
1Blank0 mL
Del K
0D. Unit
pHMolarity
0.1 mol/L
Del Sens
0 mV
S-Timer
20 secFactor1Int 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
16End Sens
300
UnitmLOver mL
0.3 mL
FormulaD
Max.Vol.
1 mL
Digits3*1: Since the maximum change in electrode potential is shown at the first drop of this blank titration, the end
point is detected in the first drop or less volume. 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 sodium carbonate

Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

2Auto
1
1
pH
20
20
20
0.5
300
0.5
40sec
mLsec
mL

ConstantNo.
SizeBlank
Molarity
FactorKL

200.010.1
1.000052.995
0g
mL
mol/L
*2*3

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

409033240secmV
secmV

Unit
Fact2mL
FormulamL
S*F*1000/(K*M*(D-B))
Digits
4*2: Purity of sodium carbonate / 100*3: It is the mass (g) of sodium carbonate that reacts with 1 mol of hydrochloric acid by the reaction formula(1) and (2), which is a half value of the formula amount (105.99) of sodium carbonate.

Measurement results
Results of factor standardization measurement
SampleBlank

Sodiumcarbonate

Measurement
No.
1231
2
3

Samplesize (g)0.14820.14860.1646

Blank measurement

Titrant
volume (mL)
0.010
0.0100.010
27.68427.76530.825

Factor
1.01051.0103
1.0079Statistical results

Avg.

0.01 mL

Avg.
SDRSD

1.010
0.001
0.14 %

Factor standardization measurement

Examples of titration curves

5. Note(1) Setting of measurement condition parameters
The neutralization reaction of sodium carbonate proceeds in two steps as shown in the reaction formulas (1)and (2). If titration is performed while dynamic controlling of the increment volume from the start ofmeasurement, two inflection points can appear as shown in the below figure. To detect the second inflection
point as the end point, it is necessary to set not to detect the first inflection point. In this report, the parameter"CP mL" is set, and the amount of titrant that exceeds the first inflection point is dispensed at the start ofmeasurement, and then titration is performed with dynamic controlling of the increment volume to detect thesecond inflection point. The 20 mL set for the parameter “CP mL” was determined by the known reaction ratiosof hydrochloric acid to sodium carbonate and preliminary tests shown below.
1 mL of 0.1 mol/L hydrochloric acid = 5.2995 mg of sodium carbonateFrom this reaction ratio, 0.15 g of sodium carbonate consumes about 28 mL of the titrant until the second
inflection point, and since the first inflection point appear at a half of that titrant volume, it can be expected tobe about 14 mL.
The set value for the parameter “CP mL” can be set to about 2 mL before the end point (26 mL in this case),
but it was set to 20 mL in consideration of fluctuations in the sampling weight.
Otherwise, to prevent the detection of the first inflection point as the end point while keeping two inflection
points on the titration curve as shown in the figure below, the parameter "DP mL" is set to 20 mL for instead of“CP mL”. Even if an inflection appears, it will not be detected as the end point until the titration volume
exceeds the parameter “DP mL” set value.

Titration curve showing two inflection points with setting “DP mL” to 20 mL(2) About the effect of the parameter “CP mL”
The parameter “CP mL” has the effect of shortening the measurement time. In this case, the measurement
time was 9 to 10 minutes when the “CP mL” was not used, whereas it was 5 to 6 minutes when it was set to 20mL. In addition, this sample solution at the start of measurement is strongly alkaline and it tend to absorbs
carbon dioxide in the air to generate sodium carbonate, which can cause variations in neutralization titration.
By using the parameter “CP mL”, the strongly alkaline sample at the start of measurement is quickly brought toneutral pH, which leads to improvement in repeatability.

Keywords：Factor standardization, Neutralization titration, Hydrochloric acid, Sodium carbonate※Depend on the configuration of instrument, ,some of measurement may not possible