In: Chemistry
When adding a common ion I know that you should have a low molar
solubility but I got a high molar solubility 0.0376 and I was
wondering what could be some reasons for me to get this? Could it
be contamination of the solution?
For example, the original was Ca(OH)2 and I got a molar solubility
of .022 and a Ksp of 4.26E-5
and when adding a common Ion CaCl2 I got a molar solubility of
.0376
Can you please help me understand why i got these results and why they don't support Le Chateliers principle? Thank you I would really appreciate it.
Ca(OH)2-------->Ca+2 + 2OH-
KSP= [Ca+2][OH-]2= 4.26*10-5
let x= molar solubility of Ca(OH)2, then[ Ca+2]=x and [OH-]= 2x
hence x*4x2= 4.26*10-5, x= molar solubility = 0.022
when CaCl2 is added, this suppliments, Ca+2 hence
Ca+2= 0.022+x and [OH-]= 2x
KSp= (0.022+x)*4x2= 4.26*10-5
when solved using excel, x= 0.01661
this is the solubility of Ca(OH)2 now. CaCl2 is more soluble in water than Ca(OH)2. This leads to precipitation of some of Ca(OH)2. The added CaCl2 suppliments of Ca+2. hence Ca+2 concentration increases. Since Solubility product does not change upon addition, less of OH- dissolves.