Chemistry: Concepts and Applications

Chapter 14: Acids , Bases, and pH

Problem of the Week

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Modern Medicine
Many modern medications have their origin from plants. An example of this is the use of mixtures extracted from the bark of white willow trees to relieve pain and reduce fever. The Chinese, Egyptians, and Aboriginal people knew the healing properties of willow bark for thousands of years. Writing of Hippocrates in Fourth Century B.C. mentioned chewing the bark of willow trees (Salix alba) to relieve pain and fever and facilitate birth. Chemists began to study the underlying chemistry of willow bark in the early 1800's and the active ingredient, salicin, was isolated. . In 1835, Karl Lowig isolated salicylic acid and later in the century it was discovered that salicin is acted on in the human stomach producing salicylic acid. Felix Hoffmann began experimenting with salicylic acid in 1890 to help his arthritic father. His research uncovered the long-ignored synthesis of acetylsalicylic acid by Charles Gerhardt in 1853 and Hoffmann devised a better way to synthesis aspirin, acetylsalicylic acid.

2-Hydroxybenzoic acid or Salicylic acid HC7H5O3
  
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<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078617987/179001/POWproblem_2.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> Calculate the Ka for salicylic acid if 0.100 M solution of salicylic acid has a pH of 1.98.
  
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Another plant with many medicinal uses is Aloe Vera. One of the first known written documentation of Aloe Vera properties was found on Sumerian clay tablets dating back to 2200 BC. Aloe Vera gel is often used to relieve pain and analysis shows that the gel contains salicylic acid. The Chinese also found this plant to be effective is treating "worm fevers" or infections caused by parasitic worms such as filariae, hookworms, pinworms, and whipworms. Aloe Vera contains cinnamic acid, HC9H7O2, which is an anthelminitic. An anthelminitic agent destroys or prevents infection caused by parasitic worms.

Cinnamic acid or Phenylacrylic acid, HC9H7O2
  
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<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078617987/179001/POWproblem_6.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> Calculate the Ka for cinnamic acid if 0.100 M solution of salicylic acid has a pH of 2.64.
  
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078617987/179001/POWproblem_7.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> Calculate the molarity of a solution of cinnamic acid if 25.2 mL of 0.200 M KOH is required to neutralize a 100.0 mL sample.
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078617987/179001/webLinks.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (1.0K)</a> Useful Web Sites:
Oh Willow, Don't Weep
Medicinal Plants
A Brief History of Organic Compounds Related to Aspirin
To Your Health: Take two: Aspirin
ScienceNet: Chemistry - What medicine is made from willow bark?
The Chemistry of Aloe Vera
Aloe Vera
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