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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Write the ionization equation and acid ionization constant expression for salicylic acid. |
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Calculate the Ka for salicylic acid if 0.100 M solution of salicylic acid has a pH of 1.98. |
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Determine the molarity of a salicylic acid solution if it takes 35.6 mL of a 0.125 M NaOH solution to neutralize 50.0 mL of the acid solution.
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What salt is formed from the neutralization of salicylic with sodium hydroxide?
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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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Write the ionization equation and acid ionization constant expression for cinnamic acid. |
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Calculate the Ka for cinnamic acid if 0.100 M solution of salicylic acid has a pH of 2.64. |
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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.
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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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