Milk of magnesia, which is an aqueous suspension of magnesium hydroxide, is used as an antacid in the reaction below. How many molecules of hcl would have to be present to form 75. 82 g of mgcl₂? mg(oh)₂(s) + 2 hcl(aq) → 2 h₂o(l) + mgcl₂(aq).