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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Kneelo on May 05, 2004, 03:04:59 AM

Title: Precipitates
Post by: Kneelo on May 05, 2004, 03:04:59 AM

Hi
If I mix Cr2(SO4)3 + NaOH a precipitate is formed , but I'm not sure which ! Is it Cr2OH or Na(SO4)3 any sugestions would be appreciated .
Thanks Kneelo

Title: Re:Precipitates
Post by: AWK on May 05, 2004, 05:24:22 AM

Cr₂(SO₄)₃ + 6NaOH = 2 Cr(OH)₃(s) + 3Na₂SO₄

Title: Re:Precipitates
Post by: jdurg on May 05, 2004, 07:17:41 AM

If memory serves me correctly, all alkali metal salts are soluble.  

Title: Re:Precipitates
Post by: AWK on May 05, 2004, 10:20:22 AM

If memory serves me correctly, all alkali metal salts are soluble.  
 It depends on anion. KClO₄, K₂[PtCl₆ ], K₂Na[Co(NO₂)₆ ] are poor soluble, Na[Sb(OH)₆ ], Li₂CO₃,
Rb₂Na[Co(NO₂)₆ ], Cs₂Na[Co(NO₂)₆ ] also. Poor solubility means in this case less than 1g/L, sometimes a few mg/L.

Title: Re:Precipitates
Post by: hmx9123 on May 06, 2004, 11:17:54 PM

Remember, everything is soluble, the question is how soluble.  Even things that you normally think of as incredibly soluble, like sodium chloride and sodium sulfate, can precipitate under the right conditions.  I have actually run a reaction before in which I had sodium sulfate precipitate out on me.  For a good look at inorganic solubilities, try the CRC handbook of chemistry and physics; the older editions contain inorganic compound solubility constants.  Lange's Handbook of chemistry also gives a lot of constants, but many are given as equilibrium constants.