Sodium phosphate is added to a solution that contains 0.0046 M aluminum nitrate and 0.051 M calcium chloride.

Sodium phosphate is added to a solution that contains 0.0046 M aluminum nitrate and 0.051 M calcium chloride. The concentration of the first ion to precipitate (either Al3+ or Ca2+) decreases as its precipitate forms. What is the concentration of this ion when the second ion begins to precipitate?