J.R. S. answered 02/21/22
Ph.D. University Professor with 10+ years Tutoring Experience
2HCl + Mg(OH)2 ---> 2H2O + MgCl2 ... balanced equation
(a). Limiting reactant would be HCl since it takes twice as much HCl as Mg(OH)2 according to the balanced equations. Thus, the 3.5 mols of HCl will determine how much MgCl2 can be made.
3.5 mols HCl x 1 mol MgCl2 / 2 mols HCl = 1.75 mols MgCl2 can be formed
(b). For this question, we need to convert to moles from the grams.
Molar mass HCl = 36.5 g/mol
Molar mass Mg(OH)2 = 58.3 g/mol
mols HCl = 3.5 g HCl x 1 mol / 36.5 g = 0.0959 mols HCl
mols Mg(OH)2 = 3.5 g Mg(OH)2 x 1 mol / 58.3 g = 0.0600 mols Mg(OH)2
Once again, HCl is limiting because there isn't twice as much HCl as Mg(OH)2 which would be required according to the balanced equation.
Mass MgCl2 formed = 0.0959 mols HCl x 1 mol MgCl2 / 2 mol HCl x 95.2 g MgCl2/mol = 4.6 g MgCl2
(c). % yield = actual yield / theoretical yield (x100%) = 2.6 g / 4.6 g (x100%) = 57% yield