J.R. S. answered 10/13/17
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2Al(s) + 3MgCl2(aq) ==> 2AlCl3(aq) + 3Mg(s) <-- Balanced equation
Determine which reactant is limiting:
moles Al present = 45.56 g Al x 1 mol Al/26.98 g = 1.688 moles Al
moles MgCl2 present = 86.9 g MgCl2 x 1 mol MgCl2/95.21 g = 0.909 moles MgCl2
Limiting reactant is MgCl2 based on mole ratio of 2 Al : 3 MgCl2 and 1.688 Al : 0.909 MgCl2
Now you can determine moles of product (AlCl3) will be produced:
0.909 moles MgCl2 x 3 moles Mg/3 moles MgCl2 = 0.909 moles AlCl3 produced <-- Answer in moles
0.909 moles AlCl3 x 133.3 g/mole = 121 g AlCl3 produced <-- Answer in grams