Question

Lab Question - Synthesis of Aspirin

Data values given:

Mass of salicylic acid: 1.02 g

Mass of 50 mL beaker plus dry product: 31.0558 g

Mass of empty dry beaker: 29.5548 g

Mass of product: 1.5010 g

1a) Show a complete calculation of how you calculated the number of moles of salicylic acid. Make sure your complete calculations are clear, complete, and correct.

1b) Theoretical number of moles of aspirin produced?

1c) Show a complete calculation of how to calculate the mass of theoretical yeild?

1d) Show a complete calculation of how you calculated the percent yield?

1e) In practice, the actual yield of a product can be much lower than the theoretical yield. Explain why this may occur, citing two possible causes. Please be clear and concise

1f) How does the melting point of a mixture compare with that of a pure substance? Discuss at least two characteristics. Please be clear and concise.

Answer 1

Synthesis of aspirin

1a) mass salicylic acid = 1.02 g

molar mass salicylic acid = 138.121 g/mol

moles salicylic acid = mass/molar mass

                                = 1.02 g/138.121 g/mol

                                = 0.0074 moles

1b) 1 mole salicylic acid produces 1 mole of aspirin

so moles of aspirin formed = 0.0074 moles

1c) Theoretical yield of aspirin = moles of salicylic acid x molar mass aspirin

                                                 = 0.0074 moles x 180.157 g/mol

                                                 = 1.330 g

1d) actual yield of aspirin = 1.501 g

percent yield = actual yield x 100/theoretical yield

                     = 1.501 g x 100/1.330 g

                     = 112.86%

1e) The actual yield is higher than theoretical yield, which could be because the product is not dry, or the starting material was incorrectly measured and higher amount of salicylic acid was taken than assumed.

1f) The melting point of product is much lower than the literature value which could be due to the product being not dry and has water in it.