For every mole of phosphorous trichloride, there are three moles of HCl. Converting to mass 1 gram of phosphorous trichloride, 0.7961 grams of HCl. Hence, for 62.0 grams of PCl3, there are 49.36 grams of HCl produced. The actual yield is 42.0 grams of HCl. The yield is 42/49.36 or equal to 85.10 %.
