Question

Magnesium oxide (2.00 grams) is added to 10.0 cm3 of 2.00 M hydrochloric acid. Calculate which reactant is in excess and the number of mole by which it is in excess?

Answer 1

Balanced equation betwewen magensium oxide and hydrochloric acid is

MgO + 2HCl -----> MgCl₂   + H2O

number of moles of magnesium oxide = 2.00g / 40.3044 g.mol^-1 = 0.0496mole

molarity of HCl = number of moles of HCl / volume of solution in L

2.00 = number of moles of HCl / 0.01 L

number of moles of HCl = 2.00 * 0.01 = 0.02 mole of HCl

from the balanced equation we can say that

1 mole of MgO requires 2 mole of HCl so

0.0496 mole of MgO will require

= 0.0496 mole of MgO *(2 mole of HCl / 1 mole of MgO)

= 0.0992 mole of HCl is required

but we have 0.02 mole of HCl so HCl is in limiting reactant and magnesium oxide (MgO) is excess reactant

from the balanced equation we can say that

2 mole of HCl requires 1 mole of MgO so

0.02 mole of HCl will require 0.01 mole of MgO

number of moles of excess reactant = 0.0496 mole - 0.01 mole = 0.0396mole

Therefore, the number of moles of excess reactant will be 0.0396