Hey there !
Molecular Weight: 262.86 g/mol
Volume in liters : 1,000 mL => 1,000 / 1000 => 1 L
Number of moles of solution :
number of moles = volume x molarity
number of moles = 1 x 0.3 => 0.3 moles
Therefore:
1 mole Mg₃(PO₄)₂ ------------------- 262.86 g
0.3 moles ----------------------------- mass of Mg₃(PO₄)₂ ??
mass of Mg₃(PO₄)₂ = 0.3 x 262.86 / 1
mass of Mg(PO₄)₂ => 78.858 g
Hope this helps!
