1977 Volume 26 Issue 6 Pages 379-383
The precipitates obtained according to the conventional procedure described in textbooks were investigated by the optical microscope observation and X-ray diffraction analysis. It was found that morphology of the precipitate formed by the reaction between lead(II) and chromate ions depends on the conditions of the precipitation as follows. The monoclinic lead(II) chromate (the stable form at room temperature) was formed from a weakly acidic solution containing no or a small amount of ammonium acetate. On the other hand, fine particles of the orthorhombic lead (II) chromate (the unstable form at room temperature) were formed from a nearly neutral solution containing no or a small amount of ammonium acetate at room temperature. And fine particles of an unknown lead-chromate compound were formed from a nearly neutral and hot or warm solution containing a large amount of ammonium acetate. Both the precipitates transformed to needle crystals of the monoclinic lead(II) chromate during being left in the solution. Lead(II) sulfate was also precipitated in different shapes according to the conditions of the precipitation.
