Hydrochloric acid (HCl) is added during the precipitation process in gravimetric analysis involving barium chloride and sodium sulfate to maintain a low pH, which prevents contamination from common airborne precipitates that react with Ba2+. The addition of HCl ensures that only barium sulfate precipitates, minimizing the formation of unwanted compounds and allowing for larger crystal formation, which facilitates easier filtration. Additionally, a low pH inhibits the precipitation of hydroxides from other metals that may be present in the solution.
PREREQUISITESChemistry students, laboratory technicians, and researchers involved in analytical chemistry and gravimetric analysis who seek to understand the impact of pH and contaminants on precipitation processes.
Borek said:There is a common contaminant (present in the air) that gives precipitate with Ba2+. Low pH will drive it away.
Borek
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Borek said:Not all, only some, but your precipitate will be contaminated, thus it will not have known exact composition.
Also note, that if your solution contains other metals, in height pH their hydroxides can preciptate, which won't happen in low pH. Finally, HSO4- is a relatively weak acid, in low pH it ismostly protonated, which slows down precipitation. That's good - the slower the precipitation, the larger the crystals are and the easier filtration is.
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