if you have .103g of Mg and react it with 1M of HCl, how many moles are present in the reaction?

Question

chemical equation for the reaction:

Mg+2HCl--> MgCl2+H2

Answer 1

The question doesn't really make sense as written. First, 1 M HCl is a concentration, not an "amount" in moles. It represents 1 mol of HCl per liter. But what volume of the 1 M HCl was used? Secondly, the question asks "how many moles are present in the reaction"? How many moles OF WHAT? Mg? HCl? Both? For lack of any other information, I'll assume they are asking how many moles of Mg and HCl took part in the reaction. That being the case, we proceed as follows:

Mg + 2HCl ==> MgCl2 + H2

moles Mg = 0.103 g x 1 mol Mg / 24.3 g = 0.004239 moles Mg

moles HCl = 0.004239 mols Mg x 2 mols HCl / mol Mg = 0.008478 moles HCl

Total moles taking part in the reaction = 0.004239 + 0.008478 = 0.0127 moles (3 sig.figs.)