Alcohol, Chemistry and You
Ethyl Alcohol: What is It?
Dr. Bill Boggan

Problems

Case Study
 

Chemistry and Symbolism

Ethanol is a colorless, mobile liquid with a characteristic odor. It vaporizes quickly in air and ethanol-air mixtures will burn if the ratio of ethanol to oxygen is in a certain range and a spark supplies the energy for ignition. These are macroscopic, observable properties.

But each ethanol molecule is a microscopically small, discrete particle consisting of two carbon atoms, two hydrogen atoms and an oxygen atom, bound to each other in a certain configuration.

Chemists use symbols to describe both the macro and microscopic aspects of substances and their transformations.

In the table to the right, we see letters of the alphabet, C,H and O and numerical subscripts as telling symbols of carbon atoms bound to hydrogen and oxygen atoms with the numbers giving the number of atoms.

The ball and stick model, in which hydrogen atoms are white, oxygen is red and carbon is black, represents another way of showing ethanol. In this model we get an idea of the shape of the molecule.

But of course, molecules do not look like either of these two dimensional, incomplete, but convenient descriptions!

Your toughest job as a student of science is to develop a sense of what these symbols represent in both the micro and macro sense!

What is an alcohol?

"Alcohol" is a generic name for large group of organic chemical compounds. There are many types of alcohols. They all are derivatives of hydrocarbons in which one or more of the hydrogen atoms have been replace by a hydroxyl (-OH) functional group. Hydrocarbons are compounds with contain hydrogen (H) and carbon (C) only. The hydroxyl group imparts particular properties to the radical to which it is attached.

Alcohols are named according to the radical to which the –OH group is attached. For example if the –OH group is attached to the methyl radical CH₃ so that the compound is CH₃OH, then one has methyl alcohol. If it is attached to the ethyl (C₂H₅) radical then one has ethyl alcohol (CH₃CH₂OH) - the alcohol we consume in beverages. The general formula for alcohol is ROH, where R signifies a hydrocarbon radical attached to an -OH group. A list of some of the common alcohols is given below:

Alcohols are classified as primary, secondary, or tertiary dependent upon the number of other organic groups, denoted R, attached to the carbon atom with the hydroxyl ( –OH) group. Those with two hydrogen atoms attached to the carbon atom with the attached hydroxyl group are called primary. Those with one hydrogen atom attached to the carbon with the hydroxyl group are called secondary, and those with no hydrogen atoms attached to the carbon atom with the hydroxyl group are called tertiary. Thus, a primary alcohol has the form RCH₂ – OH; a secondary alcohol has the form R₂CH – OH: and a tertiary alcohol, the form R₃C – OH. The R groups do not need to be the same.

Ethyl Alcohol - for which the more scientific name is ethanol - is the substance that we find in beverages. For the remainder of this unit, consider the words ethyl alcohol, alcohol and ethanol to be interchangeable. An alternate representation of ethyl alcohol as a "ball and stick" molecular model appears below:

There are other molecules that contain an -OH group - an oxygen bonded to a carbon. Water, H₂O is the most common. It is not an alcohol because alcohols are defined as organic compounds that have little or no ionization of the hydrogen. Other organic compounds that contain -OH groups but are not alcohols are phenol (C₆H₅OH) and acetic acid (CH₃COOH). These compounds are not alcohols because they are acidic. The term alcohol, then, is another representation of a type of electronic structure in the molecules of substances.

Properties of Some Alcohols

Boiling Point ^oC and Flammability and Toxicity-LD₅₀
(The dose, in mg/kg, that kills 50% of test animals, generally reported for rats.)

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