What mass of calcium phosphate will I need to contain the same number of ions as 14.2 g of sodium phosphate?

1 Answer
Sep 5, 2017

Answer:

You will need 18.6 g of #"Ca"_3("PO"_4)_2#.

Explanation:

Step 1. Calculate the moles of #"Na"_2"SO"_4#

#"Moles of Na"_2"SO"_4 = 14.2 color(red)(cancel(color(black)("g Na"_2"SO"_4))) × ( "1 mol Na"_2"SO"_4)/(142.04 color(red)(cancel(color(black)("g Na"_2"SO"_4)))) = "0.099 97 mol Na"_2"SO"_4#

Step 2. Calculate the moles of ions

#"Na"_2"SO"_4 → "2Na"^"+" + "SO"_4^"2-"#

So, 1 mol of #"Na"_2"SO"_4# produces 3 mol of ions.

#"Moles of ions" = "0.099 97" color(red)(cancel(color(black)("mol Na"_2"SO"_4))) × "3 mol ions"/(1 color(red)(cancel(color(black)("mol Na"_2"SO"_4)))) = "0.2999 mol ions"#

Step 3. Calculate the moles of #"Ca"_3("PO"_4)_2#

#"Ca"_3("PO"_4)_2 → "3Ca"^"2+" + "2PO"_4^"3-"#

∴ 1 mol of #"Ca"_3("PO"_4)_2# produces 5 mol of ions.

#" Moles of Ca"_3("PO"_4)_2 = 0.2999 color(red)(cancel(color(black)("mol ions"))) × (1 "mol Ca"_3("PO"_4)_2)/(5 color(red)(cancel(color(black)("mol ions")))) = "0.059 98 mol Ca"_3("PO"_4)_2#

Step 4. Calculate the mass of #"Ca"_3("PO"_4)_2#

#"Mass of Ca"_3("PO"_4)_2 = "0.059 98" color(red)(cancel(color(black)("mol Ca"_3("PO"_4)_2))) × ("310.18 g Ca"_3("PO"_4)_2)/(1 color(red)(cancel(color(black)("mol Ca"_3("PO"_4)_2)))) = "18.6 g Ca"_3("PO"_4)_2#