A fraction in
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...
is a quantity collected from a batch of a substance in a
fractionating separation process
A separation process is a method that converts a mixture or a solution of chemical substances into two or more distinct product mixtures, a scientific process of separating two or more substances in order to obtain purity. At least one product mi ...
. In such a process, a mixture is separated into fractions, which have compositions that vary according to a gradient. A fraction can be defined as a group of chemicals that have similar
boiling point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding envi ...
s. A common fractionating process is
fractional distillation
Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation ...
, in which separation is achieved by condensing a vapor over a range of temperatures.
It is used to produce
liquor
Liquor ( , sometimes hard liquor), spirits, distilled spirits, or spiritous liquor are alcoholic drinks produced by the distillation of grains, fruits, vegetables, or sugar that have already gone through ethanol fermentation, alcoholic ferm ...
and various
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...
fuels, such as
gasoline
Gasoline ( North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When for ...
,
kerosene
Kerosene, or paraffin, is a combustibility, combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in Aviation fuel, aviation as well as households. Its name derives from the Greek (''kērós'') meaning " ...
and
diesel.
A fraction is the product of a
fractionating column, a vast chamber designed to separate different substances (such as
crude oil) based on their boiling point.
Fraction could also refer to a description of the composition of a mixture, e.g.
mass fraction or
mole fraction
In chemistry, the mole fraction or molar fraction, also called mole proportion or molar proportion, is a quantity defined as the ratio between the amount of a constituent substance, ''ni'' (expressed in unit of moles, symbol mol), and the to ...
.
For a simpler definition a fraction is a part of the fractionating column where a compound with one boiling point can be separated from other compounds with different boiling points.
References
Separation processes
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