HIRANUMA APPLICATION DATA

Automatic Titrator

Data No.

J1Apr. 5,
2019

Purity determination ofsulfuric acid

Inorganic acids &Mixed acids
1. Abstract

Sulfuric acid is one of the most elemental reagent in chemical industrial reagents. Its production amountis large and it is used in a broad range of fields. Since sulfuric acid absorbs moisture in atmosphere because ofits properties, the purity of sulfuric acid is gradually reduced. “JIS (Japanese Industrial Standards) K8951:
2006 Sulfuric acid (Reagent)” describes the determination method for purity of sulfuric acid which it is titrated
with sodium hydroxide standard solution until the color of bromothymol blue indicator changes from yellow toblue green at the endpoint. However, this report introduces an example of the potentiometric titration withsodium hydroxide for the measurement of the accurately-weighed sample.
The neutralization titration for sulfuric acid with sodium hydroxide proceeds as two step reaction because
sulfuric acid is diacid. However, the first and second dissociation of sulfuric acid cannot be discriminated dueto the leveling effect of water. Therefore the single inflection point is observed on the titration curve and thereaction formula on this measurement can be described as below.
H2SO4＋2NaOH→Na2SO4＋H2 O・・・(1)2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit:

Hiranuma Automatic Titrator COM series

Electrodes:

Glass electrodeGE-101B

Reference electrodeRE-201Z*Instead of above electrode, the following electrodes are usable.
・Glass reference combination electrode GR-501BZ…Fixed sleeve type・Glass reference combination electrode GR-511BZ…Moveable sleeve type(2) Reagents
Titrant:

1 mol/L Sodium hydroxide standard solution

3. Measurement procedure(1) Take about 1 g of sample into a 100 mL beaker and weigh accurately.
(2) Gently add 40 mL of DI water with the 100 mL beaker iced.
(3) Immerse electrodes and start titration with 1 mol/L sodium hydroxide standard solution. Perform theblank test with the same procedure of sample measurement.

4. Measurement conditions and results
Example of titration condition
Measurement of blankCndt No.
MethodBuret No.
Amp No.
D. UnitS-Timer
C.P. mLT TimerD.P. mL
End Sens
Over mL
Max.Vol.

1Auto

11pH
200001000
0.1
1sec
mLsec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKL
Unit
Formula1001.000
1.005
00mL
D

Decimal Places
Auto In Pram.

3Non

mL
mL
mol/L

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

140003328

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

109013240sec
mV
sec
mV

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

2Auto

11pH
20
0001000
0.2
40sec
mL
sec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKL
Unit
FormulaDecimal Places
Auto In Pram.

200.0150
1.000
1.005
49.04
0%g
mL
mol/L

sec
mV
sec
mV

(D-B)*K*F*M/(S*10)
3
Non

Measurement results
Measurement results of blank

Measurement results of sample

Number ofSize

Titrant

Number ofSize

Titrant

Concentration

Measurement(g)

Volume (mL)

Measurement(g)

Volume (mL)

(%)

1-

0.015

10.9868

19.32596.4432-0.0152

1.019819.97596.4630.015 mL

31.0098

19.77596.442

Avg.
(Blank)Statisticcalculation

Avg.

96.45 %

SD

0.01 %

RSD

0.01 %

Measurement of blank

Measurement of sample

Examples of titration curves

5. Note(1) Collection of sample
The sample should be collected directly to 100 mL beaker and weighed accurately. The accuracy of sample
collection influences the measurement accuracy. Please note that the sample should be carefully taken andaccurately weighed.
(2) Control of titrant
The concentrated sodium hydroxide standard solution is used as titrant in this report. The carbon dioxide
gas absorber (soda lime) on reagent bottle has to be regularly exchanged because sodium hydroxide readily
absorbs carbon dioxide gas in the air (formula (2)). The titrant contains sodium carbonate if it absorbed
carbon dioxide gas. When using this titrant, the titration curve would show the inflection points at pH
around 4 and 9 (formula (3) and (4)).
→

Na2CO3+・・・(2)2NaOH+CO2

H2 O

2Na2CO3+H2SO4→

2NaHCO3+

Na2SO42NaHCO3+

H2SO4→Na2SO42CO2+

Keywords: Sulfuric acid, Neutralization titration, Purity, JIS K8951+・・・(3)
2H2O・・・(4)