Question

A solution containing cacl2 is mixed with a solution of li2c2o4 to form a solution that is 3.5 × 10-4 m in calcium ion and 2.33 × 10-4 m in oxalate ion. what will happen once these solutions are mixed? ksp (cac2o4) = 2.3 × 10-9.
a.nothing will happen since both calcium chloride and lithium oxalate are soluble compounds.
b.nothing will happen ksp> q for all possible precipitants.
c.a precipitate will form as calcium oxalate is not soluble to any extent.
d.a precipitate will form since q > ksp for calcium

Answer 1

The correct answer is (d)

when Ksp = [Ca2+][Ca2O4-2] = 2.3 x 10^-9

So, we need to get the value of q to compare it with Ksp:

q = [Ca2+][Ca2O4-2]

when we have [Ca2+] = (3.5 x 10^-4) 

and [Ca2O4-2] = (2.33 x 10^-4)

by substitution:

q = (3.5 x 10^-4) * (2.33 x 10^-4)

   = 8.155 x 10^-8

we can see that q > Ksp

∴ the correct answer is (D) a precipitate will form since q > Ksp for calcium