posted by Erin on .
a liter of a solution saturated at 25C with CaC2O4 is evaporated to dryness giving a 0.0061 gm residue of CaC2O4. Calculate the concentrations of the ions, and the molar solubility and the solubility product constant for this salt at 25C. Show the balanced reaction.
This could be a very complicated problem; I will assume it is to considered a simple one by ignoring the ionization of H2C2O4.
0.0061 g CaC2O4 = how many mols?
0.p0061/molar mass CaC2O4 = approximately ? = (Ca^2+) = (CO4^2-)
CaC2O4 ==> Ca^2+ + C2O4^2-
Ksp = (Ca^2+)(C2O4^2-) = ?
Substitute the molar solubilities of the ions into the Ksp expression and solve for Ksp.
i get 4.76 x 10^-5 mol CaC2o4.. squaring the answer gives me a ksp= 2 x 10^-9
is this right?
Yes and no. 2 x 10^-9 is the right start. Why did you throw the other numbers away? It's hard to tell exactly how many significant figures you have (that could be 0.00610g and you just didn't type the last zero) but the 0.0061 give you at least two so you should have at least two in the answer. My calculator shows 2.265E-9. You should round that number to the correct number of s.f.