Just a qn on Gravimetric analysis

sero2000

Hi im just wondering why during precipitation, hydrochloric acid is added to the mixture of barium chloride and sodium sulphate. Does it have something to do with the PH values or what?

Borek

There is a common contaminant (present in the air) that gives precipitate with Ba[sup]2+[sup]. Low pH will drive it away.

Borek
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sero2000

Hmmm... So u mean if the HCl was not added, the barium ions would react to form some other stuff instead of reacting with the sulphate ions?

Borek

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 hight 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.

Somehow I feel presence of someone green and small...

sero2000

Lol alright dude thanks alot man =) lol someone green and small?