Dictionary of Chemistry [6th Ed.]

air pollution (atmospheric pollu-

tion)The release into the atmos-

phere of substances that cause a

variety of harmful effects to the nat-

ural environment. Most air pollu-

tants are gases that are released into

the troposphere, which extends

about 8 km above the surface of the

earth. The burning of fossil fuels, for

example in power stations, is a major

source of air pollution as this process

produces such gases as sulphur diox-

ide and carbon dioxide. Released into

the atmosphere, both these gases are

thought to contribute to the green-

house effect. Sulphur dioxide and ni-

trogen oxides, released in car

exhaust fumes, are air pollutants that

are responsible for the formation of

*acid rain; nitrogen oxides also con-

tribute to the formation of *photo-

chemical smog. See also ozone layer;

pollution.

alabasterSee gypsum.

alanineSee amino acid.

albumin(albumen)One of a group

of globular proteins that are soluble

in water but form insoluble coagu-

lates when heated. Albumins occur

in egg white, blood, milk, and plants.

Serum albumins, which constitute

about 55% of blood plasma protein,

help regulate the osmotic pressure

and hence plasma volume. They also

bind and transport fatty acids. α-lac-

talbumin is one of the proteins in

milk.

alcoholic fermentationSee fer-

mentation.

alcoholsOrganic compounds that

contain the –OH group. In systematic

chemical nomenclature alcohol

names end in the sufÜx -ol. Examples

are methanol, CH 3 OH, and ethanol,

C 2 H 5 OH. Primary alcohols have two

hydrogen atoms on the carbon

joined to the –OH group (i.e. they

contain the group –CH 2 –OH); sec-

ondary alcohols have one hydrogen

on this carbon (the other two bonds

being to carbon atoms, as in

(CH 3 ) 2 CHOH); tertiary alcohols have

no hydrogen on this carbon (as in

(CH 3 ) 3 COH): see formulae. The differ-

ent types of alcohols may differ in

the way they react chemically. For

example, with potassium dichro-

mate(VI) in sulphuric acid the follow-

ing reactions occur:

primary alcohol →aldehyde →car-

boxylic acid

secondary alcohol →ketone

tertiary alcohol – no reaction

Other characteristics of alcohols

are reaction with acids to give *esters

and dehydration to give *alkenes or

*ethers. Alcohols that have two –OH

groups in their molecules are diols

(or dihydric alcohols), those with

three are triols(or trihydric alcohols),

etc.

A

• Information about IUPAC nomenclature

air pollution 16

a

H

H H

C

OH

H C

CH 3 CH 3

OH

C

OH

tertiary alcohol (2-methylpropan-2-ol)

_

_

_

_

_

_

_

_

_

_

_

_

primary alcohol (methanol)

secondary alcohol (propan-2-ol)

CH 3 CH 3

CH 3

Alcohols

aldehydesOrganic compounds

that contain the group –CHO (the

aldehyde group; i.e. a carbonyl group

(C=O) with a hydrogen atom bound

to the carbon atom). In systematic

chemical nomenclature, aldehyde

names end with the sufÜx -al. Exam-

ples of aldehydes are methanal

(formaldehyde), HCOH, and ethanal

(acetaldehyde), CH 3 CHO. Aldehydes