Question

What is the percent yield of a reaction in which 200. g of phosphorus trichloride reacts with excess water to form 138 g of HCl and aqueous phosphorous acid (H3PO3)?

Answer 1

write the equation
figure the moles of phosphorus trichloride
the equation tells you how many moles of HCl to expect
convert that to grams
divide 138 by the expected mass * 100%

Answer 2

calculate mass