In order to calculate the yield, we first need the theoretical and actual yields since the formula is:
Percentage yield = (actual yield / theoretical yield) x 100
The theoretical yield is calculated using the reaction equation which is:
2NaNO₃ + CuCl₂ → 2NaCl + Cu(NO₃)₂
The moles of copper chloride reacting are: 31 / 134 = 0.23
So the moles of sodium chloride produced should be: 2 x 0.23 = 0.46
The mass of sodium chloride (theoretical yield) should be: 0.46 x 58 = 26.68 g
Percentage yield = (21.2 / 26.68) x 100
Percentage yield = 79.5%