電位差滴定法による四酢酸鉛を用いる亜硫酸水素ナトリウムの定量

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Potentiometric titration with lead tetraacetate as an oxidizing agent was investigated to apply for the determination of sodium hydrogen sulfite. The solution of lead tetraacetate in which 4060 vol% acetic acid was added to avoid the hydrolysis of lead tetraacetate during the titration course, was used as a titrated solution. The titration procedures are as follows: Into a 200 ml beaker, 3050 ml of glacial acetic acid and 10.00 ml of 10-110-2N lead tetraacetate were mixed, diluted to about 100 ml with distilled water, and titrated with a test solution of sodium hydrogen sulfite at an appropriate concentration. A platinized platinum wire electrode as an indicator electrode and a saturated calomel electrode as a reference electrode, connected through a 30% KNO3 agar bridge to the beaker, were used. The electrode potential after each addition of the titrant, was read within 12 minutes before and after the end point and within 58 minutes in the vicinity of the end point. A remarkable potential drop, 400500 mV per 0.10 ml of the titrant, was observed in the vicinity of the end point when both concentrations were 0.1 N in lead tetraacetate and sodium hydrogen sulfite. Sodium hydrogen sulfite over the concentration range of 10-1 10-2N could be determined within the error of ±1.0% and with the coefficients of variation of ±0.1 %, by titrating 50 vol% acetic acid solution of lead tetraacetate with the test solution of sodium hydrogen sulfite. The titration results under the proposed conditions were not affected by the change in concentration of acetic acid and temperature of the titrated solution within the range investigated. The deposits of lead sulfate on an indicator electrode were removed by rinsing it in 2N hydrochloric acid after each titration. The proposed method is a direct titration method and is better than the conventional iodometry for the standardization of sodium hydrogen sulfite because the titration is carried out without any restriction caused by the loss of sulfur dioxide.
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電位差滴定法による四酢酸鉛を用いる亜硫酸水素ナトリウムの定量

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