Question

What is the % yield of the reaction making 4.9 g of acetyl salicylic acid from 6.6 g of salicylic acid, 6.4 mL of acetic anhydride (density 1.082), and 10 drops 85 % weight phosphoric acid (density 1.685)? Molecular weights: Acetylsalicylic acid=180g salicylic acid=138g acetic anhydride= 102g

Answer 1

mass of acetic anhydride = volume x density

                                       = 6.4 x 1.082

                                      = 6.93 g

salicylic acid   + acetic anhydride ---------------------> acetyl salicylic acid

138.12g               102.09 g                                              180.15 g

6.6g                      6.93g

138.12 g salicylic acid------------------> 102.09 g acetic anhydride

6.6g salicylic acid = 102.09 x 6.6 / 138.12 = 4.89 g acetic anhydride only we need . but we have 6.93 g . so it is excess.

limiting reagent is salicylic acid

138.12 g salicylic acid ---------------> 180.15 g acetyl salicylic acid

6.6 g salicylic acid   = 6.6 x 180.15 / 138.12

                              = 8.6 g

thereotical yield = 8.6 g

actual yield = 4.9 g

percent yiled = actual yield x 100 / thereotical yield

                       = 4.9 x 100 / 8.6

                       = 56.9 %