Answer:
The grams of MgClâ‚‚ that are needed are 63.1 g
Explanation:
First of all, try to think the equation and ballance it. This is it:
3MgCl₂  +  2Na₃PO₄  →  Mg₃(PO₄)₂  +  6NaCl
Let's convert our f.u in mol
1 mol =  6.02x10²³ formula units (Avogadro's number)
So f.u / Avogadro = mol
1.33x10²³ / 6.02x10²³ = 0.221 moles.
So 1 mol of phosphate sodium comes from 3 mol of magnesium chloride.
How many mol of magnesium chloride are necessary, for 0.221 mol of phosphate.?
0.221 moles .3 = 0.663 moles.
Molar mass of MgClâ‚‚ is 95.2 g/m
0.663 moles . 95.2 g/m = 63.1 g