Question

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!

Answers

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

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