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Percent Solutions

Calculations for percent mass and percent volume solution concentrations

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From Bench to Batch

From Bench to Batch

Credit: Linda Bartlett
Source: https://commons.wikimedia.org/wiki/File:Drug_synthesis.jpg
License: CC BY-NC 3.0

A typical chemistry problem involving amounts of material may read like this:

You wish to synthesize ethyl acetate as a part of a lab dealing with esters. You can write the equation and see the molar relationships between the two starting materials (ethanol and acetic acid). But the ethanol is in a percent solution (95% ethanol) and the acetic acid is a liquid. Knowing moles is helpful, but your balance and graduated cylinder are not calibrated in moles. Some more math is needed before you know how much of each material to measure out for your reaction.

Why It Matters

  • Laboratory synthesis of a compound often is complicated, but does not involve a lot of material. A typical bench synthesis of aspirin in the undergraduate lab may involve using 2-3 grams of the salicylic acid starting material. From this you would expect to get somewhere between 2-3 grams of aspirin, depending on how much material you used at the start. You can use molar relationships to determine how much product you expect to get, realizing that you will never obtain 100% of the theoretical yield.
  • Industrial production obviously uses much larger amounts of materials. Whenever possible, liquids would be used since volume is easier to measure. However, the salicylic acid comes in solid form and must be weighed out. The solid material is then mixed with other reagents and processed for a period of time (up to several hours depending on the specifics of the reaction) before crystallization and further purification.
  • Environmental issues are a major concern for the pharmaceutical industry. The lab synthesis of a few grams does not create much environmental waste, but the amounts of chemicals employed industrially pose significant issues. Also, yield must be carefully monitored and managed. A one percent increase in the yield in a batch run that might produce 1500 kilograms of product can be significant in terms of cutting costs of manufacture.
  • Credit: Steve Jurvetson
    Source: http://www.flickr.com/photos/jurvetson/2122946825/
    License: CC BY-NC 3.0

    Large scale production of chemicals require large scale equipment. This is mixer for viscous or sticky liquids [Figure2]

  • Watch a video about aspirin synthesis at the link below:


Show What You Know

Use the links below to learn more about industrial pharmaceutical processes. Then answer the following questions.

  1. Who developed the first aspirin?
  2. How large is a typical reaction vessel used for aspirin production?
  3. If the mass of acetic anhydride used is 1532 kg dissolved in 1200 kg toluene, what is the percent solution?
  4. What happens to the acetylsalicylic acid after it has been produced?

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    Image Attributions

    1. [1]^ Credit: Linda Bartlett; Source: https://commons.wikimedia.org/wiki/File:Drug_synthesis.jpg; License: CC BY-NC 3.0
    2. [2]^ Credit: Steve Jurvetson; Source: http://www.flickr.com/photos/jurvetson/2122946825/; License: CC BY-NC 3.0

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