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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: 113zami on April 15, 2009, 07:45:38 PM

Title: Precipitation Problem
Post by: 113zami on April 15, 2009, 07:45:38 PM

I took a chem test on line and guessed on this problem and got it right.. but when I reviewed it now .. I don't understand it

http://mysowar.wordpress.com/files/2009/04/percipetate.jpg (http://mysowar.wordpress.com/files/2009/04/percipetate.jpg)

First of all I don't understand where it says :

This sequence shows (assuming equal anion concentrations, as must be done here) that PbCO3 is less soluble than PbI2, and PbI2 is less soluble than PbSO4.

How can we make the above assumption when we don't know how fast each precipitate precipitated compared to the others ?


I also don't understand
if PBCO3 is less soluble than PBI2 and PBSO4.. how can Co3(2-) be the first to precipitate ?

thanks in advance

Title: Re: Precipitation Problem
Post by: Borek on April 16, 2009, 03:13:07 AM

Quote from: 113zami on April 15, 2009, 07:45:38 PM

How can we make the above assumption when we don't know how fast each precipitate precipitated compared to the others ?

Based on the composition of solutions used.

Quote

I also don't understand
if PBCO3 is less soluble than PBI2 and PBSO4.. how can Co3(2-) be the first to precipitate ?

I don't understand what you don't understand. How do you expect more soluble salt to precipitate first and leave less soluble salt inthe solution? It doesn't make logical sense.

Title: Re: Precipitation Problem
Post by: AWK on April 16, 2009, 04:53:23 AM

The sequence of reaction is not correct. The highest solubility show PbI2, not PbSO4.