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Alkanes Notes

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Unit 1: 6 Alkanes


Petroleum is a non-renewable fossil fuel made from the natural decay of plants and marine animals over millions of years in the absence of air.
-mixture containing mainly of alkanes
-has no use in its raw form, so in order to meet high demand products must and be separated.

FRACTIONAL DISTILLATION A FRACTION is a mixture of hydrocarbons with similar chain lengths and therefore similar properties e.g. boiling points. Crude oil separated in a FRACTIONATING TOWER.
-Energy is needed to break the Van der Waals' forces between molecules and separate the crude oil.

Outline the essential features of fractional distillation (4 marks) i.Separation of the fractions depends on the fractions having different boiling points. ii.Boiling point depends on the chain length of the molecule (longer chain have higher boiling points) iii.A temperature gradient exists in the column - being cooler and the top and hotter at the bottom iv.Shorter molecules with lower boiling points condense at the top of the column. Explain the trend in boiling points of alkanes (2 marks)

• The boiling point of alkanes increase as the molecules become larger

• Larger molecules have more electrons

• They have stronger Van der Waals' forces between molecules Explain the effect of branching on boiling points of alkanes (2 marks) The boiling point of an alkane decreases with increasing branching because;
- there is less surface contact
- the Van der Waals' forces are weaker between molecules



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