Just a qn on Gravimetric analysis


by sero2000
Tags: analysis, gravimetric
sero2000
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#1
Jun16-08, 01:47 AM
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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?
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Borek
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#2
Jun16-08, 03:52 AM
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There is a common contaminant (present in the air) that gives precipitate with Ba[sup]2+[sup]. Low pH will drive it away.


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sero2000
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Jun16-08, 04:05 AM
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Quote Quote by Borek View Post
There is a common contaminant (present in the air) that gives precipitate with Ba[sup]2+[sup]. Low pH will drive it away.

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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?

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Jun16-08, 06:05 AM
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Just a qn on Gravimetric analysis


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.

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sero2000
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#5
Jun16-08, 09:35 AM
P: 21
Quote Quote by Borek View Post
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...
Lol alright dude thanks alot man =) lol someone green and small?


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