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Help with Lab Calculations

  1. Apr 2, 2014 #1
    1. The problem statement, all variables and given/known data

    Hello,

    I'm looking for some help on how to perform some lab calculations. We recently did a lab on the Preparation of Geometric Isomers. We were preparing the Cis and Trans isomers of butenedioic acid, i.e Fumaric and Maleic Acid. The Maleic acid was done by reacting Maleic anhydride with water, and the Fumaric acid was obtained by using the maleic acid filtrate and a reflux apparatus with HCl. Here is the data I obtained:

    Maleic Anhydride Used: 4.99g
    Impure Fumaric Acid: 1.24g
    Pure Fumaric Acid: 0.82g
    Pure Maleic Acid: 0.78g
    8mL was added to the anhydride and heated at the beginning

    I am supposed to calculate the theoretical yield for the experiment, but I cannot seem to find a balanced equation to use. I believe I am supposed to calculate the amount of product (fumaric+maleic) that can be produced from 4.99g of Maleic Anhydride. I also think that for every 1 mol of Maleic acid, there should be 1 mol of Fumaric produced (since they are isomers).


    2. Relevant equations

    C4H2O3 + H2O →C4H4O4


    3. The attempt at a solution

    Is this how I would go about it?

    C4H2O3 + H2O →C4H4O4

    Calculate the amount of Maleic acid produced (using the anhydride as the limiting reagent), and since the fumaric is just an isomer, this should be the theoretical yield?

    Thank you for your help!!!
     
  2. jcsd
  3. Jan 28, 2017 #2

    TeethWhitener

    User Avatar
    Science Advisor
    Gold Member

    The theoretical yield for what? It seems from the description given that the goal of the lab was to start with maleic anhydride, hydrate to get maleic acid, then isomerize to get fumaric acid. But your numbers don't work out (given the fact that you report more fumaric acid than maleic acid, and even 100% yield would give you at most the same amount).

    To answer generally how one would find the percent yield of a reaction, you start with a balanced chemical equation and the mass (or concentration) of your starting materials, then you determine how many moles of the limiting reagent you start with. You use this number along with the balanced equation to determine how many moles of the final product you would end up with if you had a perfect 100% yield. This number is your theoretical yield. Then you use the mass (or concentration) of the final product you obtain to get a number of moles for your final product. This is your actual yield. Divide actual by theoretical and multiply by 100 to get the percent yield.
     
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