Vitamin C (L-ascorbic acid) has received much attention lately, as a result of claims that it can cure various diseases, ranging from the common cold to cancer. It is known that vitamin C is an antioxidant and is required for connective tissue synthesis. It is also used for treatment of rheumatoid arthritis. Vitamin C is readily oxidized by iodine in an acidic solution
May
12
Determination of Vitamin C in A Table
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Applications of chemistry, Biochemistry, Chemistry Experiments | 
05 12th, 2009| 
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May
12
Vitamin C Content of Foods
admin | Applications of chemistry, Biochemistry, Chemistry Experiments | 05 12th, 2009| No Comments »Vitamin C is an essential component of the diet for humans and some animals becausewe lack the enzymes to make this substance from its natural precursor, glucose. A deficiency ofvitamin C leads to a disease known as scurvy, characterized by hemorrhages throughout thebody, which are especially noticeable on the gums and around the mouth and other areas of theskin with abundant vascularization (blood vessels). It is an essential cofactor in the synthesis ofthe protein collagen, which connects cells in the body, especially in the blood vessels.The disease scurvy was described as early as 1500 BC. In the winter of 1535, a group of110 French explorers with Jacques Cartier were stranded along the St. Lawrence River andbecame afflicted with scurvy. Several of the men died and many were totally incapacitated bythe disease before the Native Americans came to their rescue and recommended a concoctionfrom a local evergreen tree that cured the survivors. The European name for the tree isarborvitae, or tree of life. Lind investigated the causes of scurvy among British sailors in 1747and found those given citrus fruits regularly did not develop scurvy, while sailors receivingvarious other dietary supplements did. He concluded there was an antiscurvy or “ascorbutic”factor in the citrus fruits that prevented the disease. The chemical structure for the ascorbuticfactor was not determined until the early 1930’s and was named ascorbic acid.The recommended dietary allowance (RDA) for vitamin C is 60 mg for adults, and higherfor pregnant and lactating women. This is an amount that is sufficient to prevent scurvy,although there is a lot of controversy over how much vitamin C is needed for a healthyindividual. Some people claim that large doses of vitamin C will help to ward off colds,although there is not complete agreement on this aspect of its actions, primarily becauseindividuals usually respond differently to various drugs and nutrients.In this laboratory you will measure the amount of vitamin C in various beverages bytitration with iodine solution. Some beverages will be supplied, but each student is encouragedto bring in a sample of his or her choosing to analyze for its vitamin C content. Iodine (I2) reactswith ascorbic acid to produce iodide ion and dehydroascorbic acid.
May
12
Solutions
A solution is a homogeneous mixture of two or more components. The dissolving agent is the solvent. The substance which is dissolved is the solute. The components of a solution are atoms, ions, or molecules, which makes them 10-9 m or smaller in diameter.
Example: Sugar and Water
Suspensions
The particles in suspensions are larger than those found in solutions. Components of a suspension can be evenly distributed by a mechanical means, like by shaking the contents, but the components will settle out.
Example: Oil and Water
Colloids
Particles intermediate in size between those found in solutions and suspensions can be mixed such that they remain evenly distributed without settling out. These particles range in size from 10-8 to 10-6 m in size and are termed colloidal particles or colloids. The mixture they form is called a colloidal dispersion. A colloidal dispersion consists of colloids in a dispersing medium.
Example: Milk
More Dispersions
Liquids, solids, and gases all may be mixed to form colloidal dispersions.
Aerosols: solid or liquid particles in a gas.
Examples: Smoke is a solid in a gas. Fog is a liquid in a gas.
Sols: solid particles in a liquid.
Example: Milk of Magnesia is a sol with solid magnesium hydroxide in water.
Emulsions: liquid particles in liquid.
Example: Mayonnaise is oil in water.
Gels: liquids in solid.
Examples: gelatin is protein in water. Quicksand is sand in water.
Telling Them Apart
You can tell suspensions from colloids and solutions because the components of suspensions will eventually separate. Colloids can be distinguished from solutions using the Tyndall effect. A beam of light passing through a true solution, such as air, is not visible. Light passing through a colloidal dispersion, such as smoky or foggy air, will be reflected by the larger particles and the light beam will be visible.
