As a result of mineral erosion and biological activity, phosphate ion is common in natural waters, where it often precipitates as insoluble salts, such as Ca3(PO4)2. Calculate Qsp when [Ca2+]init = [PO43-]init = 2.161 10-6 M in a given river.

Question

As a result of mineral erosion and biological activity, phosphate ion is common in natural waters, where it often precipitates as insoluble salts, such as Ca3(PO4)2. Calculate Qsp when [Ca2+]init = [PO43-]init = 2.161 10-6 M in a given river.
Ksp of Ca3(PO4)2 = 1.2 ✕ 10-29.

DrBob222 · Answer

I don't understand the trouble you're having. Qsp is just the ion product as if it were Ksp; then you can compare with Ksp and see if the Ksp is exceeded. If so a ppt forms, if not there is no ppt.