Question

A hard-water solution contains 4.8 g of calcium chloride. How much sodium phosphate in grams should be added to the solution to completely precipitate all of the calcium

Answer 1

Answer:

4.7 g

Explanation:

The reaction that takes place is:

• 3CaCl₂(aq) + 2Na₃PO₄(aq) → Ca₃(PO₄)₂(s) + 6NaCl(aq)

First we convert 4.8 g of CaCl₂ into moles, using its molar mass:

• 4.8 g ÷ 110.98 g/mol = 0.0432 mol CaCl₂

Then we convert CaCl₂ moles into Na₃PO₄ moles, using the stochiometric coefficients of the balanced reaction:

• 0.0432 mol CaCl₂ * $\frac{2molNa_3PO_4}{3molCaCl_2}$ = 0.0288 mol Na₃PO₄

Finally we convert 0.0288 moles of Na₃PO₄ into grams, using its molar mass:

• 0.0288 mol Na₃PO₄ * 164 g/mol = 4.7 g