| HIRANUMA APPLICATION DATA | Automatic Titrator | Data No. | J1 | Apr. 5,2019 |
| Inorganic acids & Mixed acids | Purity determination of sulfuric acid |
1. Abstract
Sulfuric acid is one of the most elemental reagent in chemical industrial reagents. Its production amount is large and it is used in a broad range of fields. Since sulfuric acid absorbs moisture in atmosphere because of its 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 to blue green at the endpoint. However, this report introduces an example of the potentiometric titration with sodium 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 due to the leveling effect of water. Therefore the single inflection point is observed on the titration curve and the reaction formula on this measurement can be described as below.
| H₂SO₄ + 2NaOH → Na₂SO₄ + H₂O | ・・・(1) |
2. Configuration of instruments and Reagents
| (1) | Configuration of instruments | ||
| Main unit | : | Hiranuma Automatic Titrator COM series | |
| Electrodes | : | Glass electrode GE-101B Reference electrode RE-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 the blank test with the same procedure of sample measurement. |
4. Measurement conditions and results
Examples of titration conditions
Measurement of blank
| Cndt No | 1 | |
| Method | Auto | |
| Buret No. | 1 | |
| Amp No. | 1 | |
| D. Unit | pH | |
| S-Timer | 20 | sec |
| C.P. mL | 0 | mL |
| T Timer | 0 | sec |
| D.P. mL | 0 | mL |
| End Sens | 1000 | |
| Over mL | 0.1 | mL |
| Max Vol. | 1 | mL |
| Constant No. | 1 | |
| Size | 0 | mL |
| Blank | 0 | mL |
| Molarity | 1 | mol/L |
| Factor | 1.005 | |
| K | 0 | |
| L | 0 | |
| Unit | mL | |
| Formula | D | |
| Decimal Places | 3 | |
|
Auto In Pram.
|
None | |
| Mode No. | 14 | |
| Pre Int | 0 | sec |
| Del K | 0 | |
| Del Sens | 0 | mV |
| Int Time | 3 | sec |
| Int Sens | 3 | mV |
| Brt Speed | 2 | |
| Pulse | 8 |
Measurement of sample
| Cndt No | 2 | |
| Method | Auto | |
| Buret No. | 1 | |
| Amp No. | 1 | |
| D. Unit | pH | |
| S-Timer | 20 | sec |
| C.P. mL | 0 | mL |
| T Timer | 0 | sec |
| D.P. mL | 0 | mL |
| End Sens | 1000 | |
| Over mL | 0.2 | mL |
| Max Vol. | 40 | mL |
| Constant No. | 2 | |
| Size | 0 | g |
| Blank | 0.015 | mL |
| Molarity | 1 | mol/L |
| Factor | 1.005 | |
| K | 49.04 | |
| L | 0 | |
| Unit | % | |
| Formula | (D-B)*K*F*M/(S*10) | |
| Decimal Places | 3 | |
|
Auto In Pram.
|
None | |
| Mode No. | 1 | |
| Pre Int | 0 | sec |
| Del K | 9 | |
| Del Sens | 0 | mV |
| Int Time | 1 | sec |
| Int Sens | 3 | mV |
| Brt Speed | 2 | |
| Pulse | 40 | |
Measurement results
Measurement results of blank
| Number of measurement |
Size (g) |
Titrant Volume(mL) |
|---|---|---|
| 1 | – | 0.015 |
| 2 | – | 0.015 |
| Avg.(Blank) | 0.015 mL | |
Measurement results of sample
| Number of measurement |
Size (g) |
Titrant volume (mL) |
Concentration (%) |
|---|---|---|---|
| 1 | 0.9868 | 19.325 | 96.443 |
| 2 | 1.0198 | 19.975 | 96.463 |
| 3 | 1.0098 | 19.775 | 96.442 |
| Statistic calculation |
Average | 96.45 % | |
| SD | 0.01 % | ||
| RSD | 0.01 % | ||
Examples of titration curves
 |
 |
| Measurement of blank | Measurement of sample |
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 and accurately 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)).
| 2NaOH + CO₂ → Na₂CO₄ + H₂O | ・・・(2) |
| 2Na₂CO₃ + H₂SO₄ → 2NaHCO₃ + Na₂SO₄ | ・・・(3) |
| 2Na₂CO₃ + H₂SO₄ → Na₂SO₄ + 2CO₂ + 2H₂O | ・・・(4) |
Keywords： Sulfuric acid, Neutralization titration, Purity, JIS K8951
*Some measurement would not be possible depending on optional configuration of system.
