The influence of hydrogen peroxide and pH on the Mohr titration.
The official Japanese method for determination of chloride in hot-spring waters requires any H(2)S present to be oxidized with hydrogen peroxide in ammoniacal medium. When this was done, and the solution was titrated with silver nitrate at pH 9.7, the indicator colour changed from yellow to brownish grey, owing to reduction of silver ions to the metal by hydrogen peroxide. The effect can be eliminated by adjusting the pH to 7.0-7.5 before the titration.
Fujita
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Department of Chemistry, School of Liberal Arts and Sciences, Iwate Medical University, Honcho-dori 3-16-1 Morioka, Japan 020.