How many moles of calcium were dissolved in the solution?

Hey everyone, im not that great at chemistry and im really stuck on this problem and could use some help.

A solution contains an unknown amount of dissolved calcium. Addition of 0.803 mol of K3PO4 causes complete precipitation of all of the calcium.

Also i need to know What mass of calcium was dissolved in the solution in grams.

Thanks for your help!


To begin with, you need a solubility chart present. This would inform you that PO4 + Ca forms an insoluble product.

Now write a balanced chemical equation for the reaction taking place.

2K3PO4 + 3Ca --- Ca3(PO4)2 + 6K+

0.803 mol K3PO4 creates 0.803 mol (PO4)3-

Using the chemical equation above, you know that for every 2 moles of K3PO4, 3 moles of Ca are consumed.

0.803 mol K3PO4 x (3 mol Ca / 2 mol K3PO4) = 1.20 mol Ca

To find grams, just use the molar mass of calcium, 40.08 g / mol to convert the molar amount to grams.

1.20 mol Ca x (40.08 g /mol) = 48.3 g Ca