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some qualitative test to determine barium ion

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rchok2:
i just need to know one thing...
to determine the presence of barium ion, 1cm3 of ethanol, 2drops of 6M H2SO4 was added... i just need to know what is the function of ethanol here@_@? thanks guys

Dude:
The only function that I could possibly see for ethanol would be to control the size of the precipitate for easier visibility.

rchok2:
thanks dude... but how is that possible? i mean what does ethanol actually do to control the size of the precipitate? why does the size of the precipitate needs to be controlled? so much for the question lol thanks

Dude:
Can't answer your questions with accuracy.  However, there are commercially available instruments that measure chloride content by turbidity (light scattering by formation of insoluble silver chloride from silver nitrate- an analogous situation).  The recipe they use usually contains stuff like glycerol and other things to control the viscosity and surface tension of the solution.  If it weren't controlled precisely, the solid might lump out and not scatter the light in the same way (and thus lose quantitative capability).

FeLiXe:
you add ethanol to decrease solubility. As ethanol is less polar than water is has a lower capability to stabilize ions in solution.

In fact barium-sulfate will be a fine white precipitate right away no matter what you do. The ethanol is added only if in the same step you also want to get calcium and strontium out of the solution. Even with ethanol calcium takes a long time and it's more a jelly than a precipitate.

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