What are some examples of sources of error and how would they cause a lower percent yield?
PROCEDURE TO DO · Weigh benzocaine isolated from last day and record the mass in the raw data from last day Determine experimental melting point of benzocaine sample and record the melting point in Dispose of benzocaine sample in appropriate dump bottle. Caution: All concentrated acids, particularly conc. sulfuric acid, will burn the skin. Handle them carefully (wear gloves) and wash up immediately if you spill any on your hands. NOTE: Wash the graduated cylinder used to obtain the acid (with cold water) to remove all traces of sulfuric acid Weigh a 4.0 g sample of salicylic acid and place it in a 50 mL round bottom flask (along with some boiling stones). Make sure that there is no solid material trapped in the neck of the round bottom flask. In a dry 50 mL Erlenmeyer flask, place 10 mL of methanol and (while cooling the flask in an ice- water bath) slowly add 4 mL of concentrated (18 moL) sulfuric acid while swirling. This solution wil become very hot, therefore the addition must be done slowly. Pour the methanoW/acid mixture into the round bottom flask which contains the salicylic acid. Attach a reflux condenser and reflux the mixture for 30 minutes using a heating mantle and variac (set at-80% to start then reduce to 40-50%). The reflux must be monitored to ensure that the reflux line does not become too high. If the reflux line is too high, the product may escape from the condenser.During this reflux, the product will be visible as a small layer on top of the methanol/acid mixture. After the reflux is finished, shut off the variac and remove the heating mantle to allow the reaction mixture to cool to room temperature for a few minutes and then place an ice-water bath around the flask to cool for 4-5 minutes. Pour the chilled reaction mixture into a 125 mL Erlenmeyer flask which contains 10 mL of cold water and then rinse out the round bottom flask with a second 10 mL portion of water and add this to the Erlenmeyer flask also. Pour the resulting mixture into a separatory funnel (do not allow the boiling stones into the separatory funnel). Rinse the reaction flask (50 mL RBF) with 20 mL of ethyl acetate and pour this into the separatory funnel (do not allow the boiling stones into the separatory funnel). Rinse the Erlenmeyer flask with 20 mL of ethyl acetate and add this to the separatory funnel also. Shake the funnel with venting and after the layers have separated, drain the lower layer (methanol & sulfuric acid). The lower layer contains concentrated sulfuric acid and can be disposed of as follows. Pour the lower layer into a large volume of water in a beaker, stir to mix and then dispose of it down the drain in the fume hood followed by a copious amount of water
