ESTIMATION OF THE QUANTITY OF BARIUM SULFATE PRECIPITATE BY ITS VOLUME

Abstract

It constitutes an important teaching material in lower secondary school that the quantity of a reaction product is affected both by the concentration and volume of the reagent solutions. On this subject, the reactions yielding barium sulfate precipitate which appeared in textbooks and/or in teacher's guides were investigated to give some essential information as follows: ⅰ) Sedimentation of barium sulfate under alkaline conditions takes much time, so that the amount of precipitate can hardly be estimated by its volume in an ordinary school hour. ⅱ) Completion of its precipitation is accelerated by the addition of strong anionic polymer floeculants (eg. OA-7), which makes the volume of precipitate proportional to its quantity for a period of 5 min. ⅲ) When barium sulfate is prepared both in acidic and alkaline solutions, the similar particle size is attained for the precipitate in the two areas by the use of cationic polymer flocculants (eg. C-360). It is also able to evaluate the amount of precipitate from its volume in the same time-course. Moreover, the necessity of polymer flocculants as a teaching material was emphasized in preparing barium sulfate precipitate, by reference to the student experiments reported earlier.