356 DIY Science: Illustrated Guide to Home Chemistry Experiments
LABORATORY 2 0.1:
qUANTITATIvE ANALySIS of vITAmIN C By ACId-BASE TITRATIoN
Vitamin C is a vital part of the human diet.
A deficiency of vitamin C causes a wasting
disease called scurvy, which until the
eighteenth century plagued sailors and others
whose regular diets provided few fresh fruits
and vegetables. In fact, the chemical name
for vitamin C, ascorbic acid, is derived from
scorbutus, the Latin name for scurvy.
RIREEqU d EqUIpmENT ANd SUppLIES£ goggles, gloves, and protective clothing£ balance and weighing papers£ hotplate£ Erlenmeyer flask, 125 mL£ graduated cylinder, 100 mL£ burette, 50 mL£ ring stand£ burette clamp£ vitamin C tablet, 500 mg£ sodium hydroxide, 0.1000 m (~50 mL)£ phenolphthalein indicator (a few drops)In 1753, British Royal Navy surgeon James Lind published
a book, A Treatise on the Scurvy, which concluded that
scurvy could be prevented by including citrus fruits in the
diet, and that active cases of scurvy could be treated almost
miraculously simply by having the patient consume citrus
fruits or juices. The Royal Navy began adding lime juice to the
regular tots of rum provided to all sailors, accidentally creating
the world’s first rum punch. Scurvy disappeared, and British
sailors became known as Limeys.
EvdRE y Ay qUANTITATIvE ANALySIS
The importance of quantitative analysis isn’t limited to chemistry labs. Quantitative analysis is important in everyday life, and is
sometimes literally a matter of life and death. Here are just a few examples.
Pharmaceuticals must be of known strength and purity. Quantitative analytical techniques are used to ensure both. For
example, drug tablets and capsules are assayed using titration and other quantitative analytical techniques to make sure that
each contains the nominal dosage, within allowable limits. Conversely, it’s just as important to ensure that contaminants are
present only at or below acceptable levels. Again, quantitative analytical tests are used to verify that the drug is sufficiently
pure to be safe for human consumption.
Quantitative analysis is used to determine the content and purity of food. For example, wine is analyzed to determine the
percentage of alcohol that it contains and to ensure that contaminants such as sulfites are at acceptably low levels. When you
read the nutrition facts panel on a can of food or a bottle of soda and learn that one serving contains 3 g of fat or 8 g of protein
or 5 g of carbohydrate, you’re reading information that was obtained by quantitative analysis.
When you turn on your faucet, the water that comes out is safe to drink because quantitative analytical procedures are used
to ensure that safety. Chemists at the water department regularly test the water to determine levels of arsenic, lead, mercury,
and other dangerous heavy metals, as well as pesticides and other poisons. In poor countries, thousands of people die every
week from drinking water that contains high levels of such contaminants.
The gasoline you pump into your car is actually a complex blend of raw gasoline with numerous additives that improve
performance, increase mileage, and reduce air pollution. Because gasoline is blended in a continuous process (when fuel
delivery trucks fill up at the terminal) rather than in batch mode, gasoline is tested regularly using quantitative analysis to
ensure that the concentration of the additives is within acceptable limits.
Police officers use instrumental quantitative analysis to test the blood alcohol content of suspected drunk drivers.