QUIZ 12a. The origin of crude oil and its products

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(a) Crude oil is extracted from the Earth's . It was formed from the remains of marine which lived millions of years ago. The fuels , oil and natural have rformed by the action of heat and over millions of years, in the absence of , on material from animals and plants (organic material) which has been covered by layers of rock.

(b) Crude oil is a of a very large number of compounds. A mixture consists of or more elements or not combined together. The chemical properties of each substance in the mixture are . This makes it possible to separate the substances in a mixture by methods including distillation.

(c) Most of the compounds in crude oil consist of made up of hydrogen and carbon atoms only and are called . They can be separated into fractions, each of which contains molecules with a number of carbon atoms, by the oil and allowing it to condense at a number of different . This process is .

(d) The hydrocarbon molecules in crude oil vary in . The larger the molecules the the number of carbon atoms in the hydrocarbon, the its boiling point, the volatile it is, the less easily it flows i.e. the more it is, and the less easily it ignites, meaning the less it is, and this limits the usefulness of large hydrocarbon molecules as .