81.0% yield
First, lookup the atomic weight of all involved elements
Atomic weight of Calcium = 40.078
Atomic weight of Hydrogen = 1.00794
Atomic weight of Oxygen = 15.999
Calculate the molar mass of CaO and Ca(OH)2
Molar mass CaO = 40.078 + 15.999 = 56.077 g/mol
Molar mass Ca(OH)2 = 40.078 + 2 * 1.00794 + 2 * 15.999 = 74.09188 g/mol
Determine how many moles of CaO you started with
2.00 g / 56.077 g/mol = 0.035665246 mol
Determine how many moles of Ca(OH)2 you ended up with
2.14 g / 74.09188 = 0.028883057 mol
Looking at the formula, you should get 1 Ca(OH)2 molecule per CaO molecule used. So divide the number of moles obtained by the number of moles used to get the percent yield.
0.028883057 / 0.035665246 = 0.809837594 = 81.0%
