Carbon Dioxide

  Carbon dioxide (KAR-bun dye-OK-side) is a colorless,
odorless, tasteless, non-combustible gas that can also exist
under pressure as a clear, colorless, odorless, tasteless liquid
and as a white, snow-like solid commonly known as dry ice.
When dry ice is warmed it sublimes (passes directly from
the solid to the gaseous state without first melting) at
78.4C (-109F).
  The true nature of carbon dioxide was discovered over an
extended period of time beginning with the research of the
Flemish physician and chemist Jan Baptista van Helmont
(1580–1635?). In about 1603, van Helmont isolated a gas
produced during the combustion of wood and proved that it
was distinct from air. At the time, air was generally regarded
as an element that could not be divided into separate components.
Van Helmont called the gas gas sylvestre (‘‘wood gas’’),
a substance we now know to be carbon dioxide. Credit for
understanding the true nature of carbon dioxide also goes to
the Scottish chemist Joseph Black (1728–1799) who produced

carbon dioxide by heating calcium carbonate (CaCO3). Black
called the gas fixed air and conducted the first extensive
studies of its properties.
  The first practical use for carbon dioxide was discovered
in the mid-eighteenth century by the English chemist Joseph
Priestley (1733–1804). Priestley found that passing carbon
dioxide into water produced a sparkling, refreshing drink
that he predicted would one day become a great commercial
success. He was, of course, correct, since water containing
carbon dioxide is the basic component of which all soda
drinks are made.

  Carbon dioxide is produced in nature by a number of
reactions. Among the most common is the combustion
(burning) of the fossil fuels (coal, oil, and natural gas). The
gas is also produced during the decay of organic material,
the fermentation of carbohydrates by yeast, and the respiration
of animals. In the laboratory, the simplest and most
direct method of preparation is to treat a carbonate, such
as calcium carbonate, with an acid, such as hydrochloric
acid (HCl).
  Carbon dioxide is obtained commercially as the byproduct
of a number of industrial reactions. For example,
when calcium carbonate is heated to produce lime (CaO),
carbon dioxide is released and captured as a by-product. The
steam reforming (refining) of petroleum results in the production
of a mixture of gases known as synthesis gas, consisting
of carbon dioxide, carbon monoxide, hydrogen, and
nitrogen. Carbon dioxide can be separated from the other
components of synthesis gas for commercial uses. Carbon
dioxide also produces as a by-product of the manufacture of
ammonia (NH3) by the Haber-Bosch process.

  Carbon dioxide plays an essential role in most biological
processes that take place on Earth’s surface. Plants use carbon
dioxide as a raw material to make the carbohydrates on
which their structures are based. When animals eat plants,
those carbohydrates are then used to build and maintain
their body structures.
In addition to its role in natural processes, carbon dioxide
has many commercial and industrial applications. One of the
most important uses is in the carbonation of beverages.
Although beers and sparkling wines contain carbon dioxide
from natural sources (the fermentation of sugars by
yeasts), nearly all carbonated beverages have their carbon
dioxide added artificially. The carbon dioxide adds a zesty
taste to the beverage and helps to preserve it.

  Carbon dioxide is also used as a fire extinguishing agent.
Its use for this purpose is based on the facts that it does not
burn itself and is heavier than air. Thus, when sprayed on a
fire, carbon dioxide settles down on top of the flames and
prevents oxygen from reaching the burning material. The
carbon dioxide can be supplied in a variety of ways in a fire
extinguisher. In some devices, carbon dioxide gas is produced
as the result of a chemical reaction that occurs within
the fire extinguisher. In other devices, liquid carbon dioxide
is released from the extinguisher.
  Carbon dioxide is also used in gaseous, liquid, or solid
form as a refrigerant. As a gas, it is used as the ‘‘working
fluid’’ in refrigerators, the fluid that circulates through the
refrigerator changing back and forth from gas to liquid,
absorbing heat in the process. In the form of dry ice, carbon
dioxide is a very efficient and convenient method for cooling
objects to very low temperatures (close to the sublimation
point of carbon dioxide, about 78.4C (109F).
Some other uses of carbon dioxide include the following:
• As an aerosol propellant;
• To provide an oxygen-free atmosphere in which to conduct
welding and other operations with flammable
materials;
• In the industrial manufacture of carbonates;
• For cloud seeding to promote modifications in the
weather (increases or decreases in rain fall);
• In the fumigation of rice to preserve the product for
extended periods of time;
• As an artificial smoke in theater productions;

• As a moderator to slow down the speed of neutrons
traveling in a nuclear power plant;
• In the frozen food industry;
• To enrich the air in a greenhouse, providing additional
carbon dioxide to promote plant growth; and
• For the hardening of foundry molds and cores.
In general, carbon dioxide poses little or not threat to
humans in concentrations to which one is normally exposed.
Dry ice may pose a hazard if not handled carefully as its very
low temperature can cause damage to the skin.

Ethyl Alcohol

 

  Ethyl alcohol (ETH-uhl AL-ko-hol) is a clear, colorless,
flammable liquid with a sharp, burning taste and a pleasant,
wine-like odor. It is one of the first chemical substances
discovered and used by humans. Ceramic jugs apparently
designed to hold beer have been dated to the Neolithic Period,
about 10,000 BCE. Some scholars suggest that humans
may have learned how to make beer and incorporated it into
their daily diets even before they made and used bread. The
making and use of wine is a clear theme in Egyptian pictographs
dating to the fourth millennium BCE. There probably
does not exist a human culture today in which alcohol consumption
does not occur. Today, beverages with alcohol content
ranging as low as two to five percent (‘‘near beer’’ and
beer) to as high as 50 percent (some forms of vodka) are
known and consumed by humans. In spite of its widespread
use as a beverage, ethyl alcohol has a number of commercial
and industrial uses that account for more than 90 percent of
all the compound produced in the United States.

Ethyl alcohol is made in one of two ways: naturally,
through the process of fermentation, or synthetically, beginning
with compounds found in petroleum. Until the beginning
of World War II, more than 90 percent of all ethyl
alcohol produced in the United States and other developed
nations was made by fermentation. Waste syrup left over
from the production of sugar from sugar cane was treated
with enzymes at temperature of 20C to 38C (68F to 100F)
for 28 to 72 hours. Under these conditions, about 90 percent
of the syrup is converted to ethyl alcohol.
Over time, synthetic methods for the production of ethyl
alcohol were developed. In one such method, ethylene
(ethene; CH2=CH2) is treated with sulfuric acid and water
to= obtain ethyl alcohol. That method was popular during
the 1950s and 1960s. Then, a new method for making the
compound was invented. In that process, ethylene and water
are heated together at high temperatures [300C to 400C
(570F to 750F)] and high pressures [1,000 pounds per
square inch (6.9 megaPascals)] over a catalyst of phosphoric
acid (H3PO4). The efficiency of this method is greater than

the older method, and there are fewer environmental consequences
from making ethyl alcohol by this process.
As of 2003, about 94 percent of all ethyl alcohol was
produced by fermentation. The remainder was produced by
the phosphoric acid method.

   In 2005, 10,500 million liters (2,790 million gallons) of
ethyl alcohol were produced by fermentation methods. Of
that amount, 92 percent was used as a fuel or an additive in
fuels. Many experts suggest that consumers use a mixture of
gasoline (90 percent) and ethyl alcohol (10 percent) called
gasohol as a vehicle fuel because it burns more completely
and releases fewer harmful byproducts to the environment.
Although gasohol has not yet become very popular in the
United States, it is widely used in some other parts of the
world, most notably, in Brazil.
Of the remaining 8 percent of ethyl alcohol produced by
fermentation, half was used in industrial operations, as a
solvent or intermediary in the preparation of other chemical

compounds; and half was used in the production of alcoholic
beverages.
In 2005, about 650 million liters (170 million gallons) of
ethyl alcohol were produced by the phosphoric acid method.
Of that amount, 60 percent was used for industrial solvents
in the manufacture of toiletries and cosmetics, coatings and
inks, detergents and household cleaners, pharmaceuticals,
and other products. The remaining 40 percent was used in
the preparation of other chemical compounds, including
ethyl acrylate, vinegar, ethylamines, ethyl acetate, glycol
ethers, and miscellaneous materials.
Ethyl alcohol commonly occurs in one of three general
forms. Absolute alcohol is ethyl alcohol that contains less than
1 percent impurities, such as water. Absolute alcohol is very
difficult to make because ethyl alcohol will absorb water from
the atmosphere or any other source that is available. The ethyl
alcohol used in fuels and almost all industrial operations is a
mixture of 95 percent ethyl alcohol and 5 percent water. Both
absolute and 95 percent ethyl alcohol are extremely toxic.
Ingestion of even very small amounts of either liquid has
serious health effects that may include death.
The alcohol with which most people commonly come into
contact is ethyl alcohol mixed with water in alcoholic beverages,
such as beer, wine, gin, vodka, rum, or bourbon. In such
beverages, the concentration of ethyl alcohol ranges from a
few percent to 50 percent.
The effects produced by ethyl alcohol on the human body
depend on the type of beverage consumed and the time
taken for consumption. Drinking a 5-percent beer over an
hour has a very different effect on the body than drinking a
50-percent vodka in five minutes.
Ethyl alcohol is a central nervous system depressant.
After ingestion, it passes through a person’s stomach and
the small intestine, where it is absorbed rapidly into the
bloodstream. It then travels throughout the body, interfering
with the normal functioning of the nervous system and
producing symptoms such as drowsiness, slurred speech,
blurred vision, unsteady gait, impaired judgment, and
reduced reaction time. With greater concentrations of alcohol
in the blood, these symptoms may become more severe,
resulting in coma and death.