In chemistry, compunds are devided between organic and inorganic
compunds. Organic compounds were once thought to be produced only by
living things. We now know that any organic compound can be
synthesized in the laboratory.
There are two major ways of defining what an "organic compund" is, you
can see some variations of them in the Google Glossary:
The broadest definition is "any compund containg carbon", while a
stricter definition is "any compund containing at least one
carbon-hydrogen or carbon-carbon bond". The later definition is the
one that is used by most scientists (and textbooks), and I'll use that
in answering your question.
C2H5 is the hydrocarbon ethane, and has the following structure:
H - C - C - H
Hydrocarbons consist of only hydrogen and carbons connected with
carbon-hydrogen and carbon-carbon bonds. All hydrocarbons are organic
NaOH (sodium hydroxide) does not contain any carbon, and cannot be an
C2H5OH is ethanol (the alcohol found in beer, wine and spirits) and
has this structure:
H - C - C - OH
It is an organic compund. All alcohols are organic compounds.
HCI - I considert this to be a typing error for HCl (hydrocloric
acid). This is not an organic compund, as it does not contain any
carbon-carbon or carbon-hydrogen bonds.
CO is carbon monoxide. This compound does not contain any
carbon-carbon or carbon-hydrogen bonds, and is inorganic.
C18H36OH is stearic acid with this structure:
H H H H H H H H H H H H H H H H H OH
| | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | |
H H H H H H H H H H H H H H H H H
You will probably tell that this is an organic compund, as it does
contain both carbon-carbon and carbon-hydrogen bonds. Stearic acid is
in fact an "organic acid", that's basically a hydrocarbon with a
carboxyl group (-COOH) somewhere in its structure.
To sum it up:
NaOH, HCl and CO are inorganic compunds, the rest are organic compunds.