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Stoichiometry help

  1. Dec 10, 2007 #1
    1. The problem statement, all variables and given/known data
    Saponification is the process by which soap is made. A triglyceride is reacted with NaOH to produce a carboxylic acid salt (the soap) and glycerol
    Lard, mostly made of trioleic acid (TOA) is used with Lye (NaOH) in homemade variations
    molar mass of TOA is 848g/mol
    molar mass of resulting soap is 304g/mol

    2. Relevant equations
    TOA + 3NaOH --> 3 Soaps+ 3 glycerol

    Question: if you want to make a 405g bar of soap with no excess lard or lye what amounts of lard and lye are needed.

    3. The attempt at a solution

    i have no idea how to do this problem. I know you start with 405g soap/1 to 1mol soap/(idk how much soap weighs per mol)
  2. jcsd
  3. Dec 10, 2007 #2


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    Firstly, you must realize that this question is a bit hypothetical since animal fats are saturated, unlike 'trioleic acid'. That would be tristearic acid in your nomenclature. An alternative nomenclature is to say 'triolein' for the glyceryl ester of oleic acid (olive oil) and 'tristearin' for the glyceryl ester of stearic acid (lard).

    You are given the molar mass of the TOA and the resulting soap in the problem but I have no idea how those numbers were arrived at... perhaps thin air? The amount of soap produced from TOA is therefore given by a ratio of these two numbers multiplied by number. Can you take it from there?
    Last edited: Dec 10, 2007
  4. Dec 10, 2007 #3


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    BTW, The correct saponification reaction (not your problem, certainly) would be:

    [tex]Triolein + 3NaOH \rightarrow\ 3 Na^+ ^-OOC-C_{17}H_{33} + 1 glycerol[/tex]

    where the formula weight of triolein is 885.4 g/mol and the formula weight of the soap is 304.4.
    Last edited: Dec 10, 2007
  5. Dec 10, 2007 #4
    a little more help

    thanks alot
    heres another wuestion i need help with

    the fuel used to power booster rockets is represented in The balanced equation
    3Al + 3NH4CIO4 ? Al2O3 + 3NO + 6H2O

    if ____e5kg Aluminum reacts with an excess of ammonium perchlorate (say____e6kg) what is the mass of nitrogen vapor produced

    im supposed to fill in the blanks with any numbers that i want but i dont know what "e5kg" and "e6kg" mean.
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