硝酸バリウム-硝酸鉛混合溶液による硫酸イオンの沈殿滴定にpHメータの利用

概要

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When the precipitimetry of sulfate is carried out in the presence of acetone in a solution, a steep change of apparent pH of the solution is found to appear near the end point of the titration. Therefore, a pH meter is useful to indicate the end point. Many titration curves were drawn with sodium sulfate solution under various conditions to find a suitable procedure for the purpose. The recommended conditions are as follows : the ratio of acetone to an aqueous solution should be 3 : 1 in a sample solution; the mixed titrant should be composed of barium nitrate and lead nitrate in their molar ratio of 10 : 1; and the concentration range of sulfate should be from 1/120 to 1/240<I>M</I> in the aqueous-acetone solution. The sulfate other than sodium salt could also be titrated after an addition of aqueous ammonia in its solution to elevate the pH to about 8. Sulfate ion in a solution of magnesium, potassium, aluminum, iron (III), beryllium and copper sulphates could be estimated by this method.
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