Need with this stoichiometry question

Hi!

HCl is the limiting reactant.

From the equation, we understand that 1 mole of Mg(OH)2 will react with 2 moles of HCl for the reaction to be complete. To find the limiting reactant we need to see which molecule is in lower quantity (in terms of moles and not mass)

Calculating the number of moles of Mg(OH)2 given

Using the formula, number of moles= mass / molecular mass

number of moles = 50.6 / 58 = ~ 0.872

Calculating the number of moles of HCl given

Number of moles = 45 / 36.5 = ~ 1.232

There are several ways to use this information  to calculate the limiting reactant. In our case, we can subtract the number of moles of Mg(OH)2 from the number of moles of HCl and check for the remainder.

If it is more than 0.872, then HCl would be in excess, with Mg(OH)2 being the limiting reactant; however, if the remainder is less than 0.872, it would mean HCl is the limiting reactant.

1.232- 0.872 = 0.36

As 0.36 < 0.872 , we see that HCl is the limiting reagent.

NOTE: this is in the case that the moles of HCl needed to complete the reaction is twice that of Mg(OH)2.

Hope this helps!