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The pre-lab is completed before performing the experiment and will be turned in at the beginning of lab. It uses the same template for every experiment and can be found on BB. For more information, see Pre-Lab Report Template page.
Below you will find the the pre-lab broken down into sections for Experiment 21 - Synthesis of Aspirin. Remember, the lab may change or be modified from semester to semester. This material is only meant to be a guide!
pre-lab guide
name, Exp#, & Title
These sections of the pre-lab or self-explanatory, but you are awarded points for completing them. Just remember to put the correct experiment number and title when filling out these sections.
Brief Description of Tasks
This is where you summarize the purpose and tasks performed in the lab from your lab manual. This should be about a paragraph long. It may be helpful to first describe the purpose of the experiment or why you are doing this experiment. This can be followed by one or two sentences on how you will be doing it. The paragraph given is an EXAMPLE.
Experiment 21 - Synthesis of Aspirin (click to enlarge)
Outline of the Experiment
This is where you outline the major steps performed in lab. The level of detail will be up to you, but more detailed steps may be useful when studying for your quizzes.
Given is an EXAMPLE and breaks down major tasks into steps for each of the parts. Remember procedures may change from semester to semester. Numbers in parenthesis give a reminder to record data on the specific numbered blank space on the data sheet. Highlighted are reagents (green) used in the experiment.
Experiment 21 - Synthesis of Aspirin Part A (click to enlarge)
Experiment 21 - Synthesis of Aspirin Part B-C (click to enlarge)
Sample Calculations
There are two main calculations you will do in this experiment. The first is calculating the theoretical yield of aspirin. The second calculation is the percent yield. These are detailed below.
Aspirin Synthesis Reaction (click to enlarge)
Theoretical Yield Calculation (remember significant figures)
From the above reaction we know the amount of salicylic acid is a 1 to 1 (1:1) ratio with the amount of aspirin. This means every mole of salicylic acid used will yield the same number of moles of aspirin. Therefore, the first step is to calculate the number of moles of salicylic acid used. Note: you are told that acetic anyhydride is in excess and salicylic acid is the limiting reagent
Mass of Salicylic Acid Used (mock value) = 276.24 g
Molar Mass of Salicylic Acid = 138.12 g
Moles of Salicylic Acid = (1)/(2) = 276.24/138.12 = 2.00 moles
To then convert the number moles of Aspirin to the expected yield in grams, we multiply the moles by the molar mass of asprin
Moles of Salicylic Acid = Moles of Aspirin —> 2 moles of Salicylic Acid makes 2 moles of Asprin
Molar Mass of Aspirin = 180.16 g
Theoretical yield of Aspirin (g) = (1)(molar mass of aspirin) = 2.00(180.16) = 360 grams
Percent Yield Calculation (remember significant figures)
From part A you will measure how much aspirin you synthesized. This will be your actual yield. Using this mass and the theoretical yield value calculated, the percent yield can be found.
Actual Yield of Aspirin from Part A (mock value) = 370 g
Mass of Theoretical Yield of Aspirin = 360 g
Percent Yield = (Actual ÷ Theoretical) x 100 = (370 ÷ 360) x 100 = 103 %
Table of Reagents
This is where you list the reagents used for this lab. Given in the example are values and reagents that should be verified on your own. Below details where you can find this information.
Chemical Name: this or the formula will be given in the lab manual. With this information you can search online for the other
Formula: see above.
Molecular Weight: search online
Physical State: lab manual
Amount to Use: lab manual; the amount can be reported as the sum amount used and further detailed (see below).
Experiment 21 - Synthesis of Aspirin (click to enlarge)