## Tuesday, November 26, 2019

### Theoretical Yield Worked Example Problem

Theoretical Yield Worked Example Problem This example problem demonstrates how to calculate the amount of reactant needed to produce a product. Problem Aspirin is prepared from the reaction of salicylic acid (C7H6O3) and acetic anhydride (C4H6O3) to produce aspirin (C9H8O4) and acetic acid (HC2H3O2). The formula for this reaction is:C7H6O3 C4H6O3 Ã¢â€ â€™ C9H8O4 HC2H3O2.How many grams of salicylic acid are needed to make 1000 1-gram tablets of aspirin? (Assume 100% yield) Solution Step 1 - Find molar mass of aspirin and salicylic acidFrom the periodic table:Molar Mass of C 12 gramsMolar Mass of H 1 gramsMolar Mass of O 16 gramsMMaspirin (9 x 12 grams) (8 x 1 grams) (4 x 16 grams)MMaspirin 108 grams 8 grams 64 gramsMMaspirin 180 gramsMMsal (7 x 12 grams) (6 x 1 grams) (3 x 16 grams)MMsal 84 grams 6 grams 48 gramsMMsal 138 gramsStep 2 - Find mole ratio between aspirin and salicylic acidFor every mole of aspirin produced, 1 mole of salicylic acid was needed. Therefore the mole ratio between the two is one.Step 3 - Find grams of salicylic acid neededThe path to solving this problem starts with the number of tablets. Combining this with the number of grams per tablet will give the number of grams of aspirin. Using the molar mass of aspirin, you get the number of moles of aspirin produced. Use this number and the mole ratio to find the number of moles of salicylic acid needed. Use the molar mass of salicylic acid to find the grams needed. Putting all this together:grams salicylic acid 1000 tablets x 1 g aspirin/1 tablet x 1 mol aspirin/180 g of aspirin x 1 mol sal/1 mol aspirin x 138 g of sal/1 mol salgrams salicylic acid 766.67Ã‚   Answer 766.67 grams of salicylic acid are needed to produce 1000 1-gram aspirin tablets.