Organic Chemistry I Lab
Organic Chemistry I Lab CHEM 333L
Popular in Course
Popular in Chemistry
This 3 page Class Notes was uploaded by Ms. Napoleon Harris on Thursday October 15, 2015. The Class Notes belongs to CHEM 333L at New Mexico Institute of Mining and Technology taught by Staff in Fall. Since its upload, it has received 33 views. For similar materials see /class/223642/chem-333l-new-mexico-institute-of-mining-and-technology in Chemistry at New Mexico Institute of Mining and Technology.
Reviews for Organic Chemistry I Lab
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 10/15/15
Calculation of Theoretical and Percentage Yields For every chemical reaction an equation can be written showing the conversion of the starting materials into the products From this equation the expected yield of a particular product can be calculated Ideally the amount of this product actually obtained should equal the amount calculated but in reality this is seldom true Competing side reactions can consume the reagents to give other frequently undesired products The reaction may reach a state of equilibrium where only a portion of the starting materials have reacted Finally part of the desired product may be lost in the reaction workup when it is separated from all its possible contaminants For a chemical synthesis it is therefore necessary to calculate the theoretical and the percentage yields Knowing the percentage yield is important because it indicates how efficiently the conversion of the reactants to the product has occurred Where cost and time are important factors the efficiency allows us to consider and compare other possible approaches in synthesizing and isolating the desired material To calculate the percentage yield you must first know the theoretical yield You can calculate it from the balanced equation and the quantities of each reactant For example in the synthesis of aspirin from salicylic acid and acetic anhydride we would write 0 CH3 0 0lt OH O H PO OH O A O A y H3 OH OH CH3 CH3 Salicylic acid Acetic anhydride Acetylsalicylic acid Acetic acid C7H603 C4H6O3 C9H804 C2H402 MW 2 138 gmol MW 2 102 gmol MW 2 180 gmol MW 2 60 gmol This equation shows that 1 mole of salicylic acid reacts with 1 mole of acetic anhydride to yield theoretically 1 mole of aspirin This 111 ratio of reactants and products of course will apply no matter what quantities are used You must realize that the theoretical yield of product will be based upon the limiting reagent if any in the reaction Thus if 0020 mole of salicylic acid reacts with 0025 mole of acetic anhydride only 0020 mole of aspirin can theoretically be produced Salicylic acid Acetic anhydride Aspirin b 0020 mole 0025 mole 0020 mole theoretically possible Remember that the limiting reagent is based upon the number of moles not the number of grams Thus in the above example 0020 mole of salicylic acid would amount to 28 grams which is more in terms of weight than the 26 grams or 0025 mole of acetic anhydride With this information we can calculate the theoretical yield for any reaction by using the equation Theoretical yield 2 moles of limiting reagent X mole mole ratio of limiting reagent to product X molecular weight of product In this example with 0020 mole of salicylic acid as the limiting reagent the result would be Theoretical yield 2 0020 moles of salicylic acid 1 mole aspirin 180 grams aspirin X 1 mole salicylic acid 1 mole aspirin 36 grams of aspirin The actual yield is simply the weight of desired product isolated With the actual yield and the theoretical yield we can calculate the percentage yield by the equation Actual yield Percentage yield 2 X 100 Theoretical yield In our example if 27 grams of aspirin were isolated the percentage yield would be 27 grams Percentage yield 2 x 100 75 36 grams In some experiments the objective is the isolation of a natural product rather than the synthesis and purification of a reaction product In these cases the percentage yield refers to the percentage of the substance isolated based upon the weight of original material For example if 024 grams of caffeine were isolated from 200 grams of tea the percentage yield would be Weight of substance isolated Percentage yield 2 x 100 Weight of original material 024 grams x 100 12 200 grams Observe that there is no calculation of the theoretical yield for this type of experiment Why
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'