ALKANES AND FRACTIONAL DISTILATION

Question 1

what are alkanes

Answer 1

saturated hydrocarbons consisting of only carbon carbon and carbon hydrogen single bonds
among the least reactive organic compounds
used as fuels and lubricants so very important to industry
main source of alkanes is crude oil

Question 2

general formula of alkanes

Answer 2

CnH2n+2

Question 3

general formula for cycloalkane

Answer 3

CnH2n

Question 4

what are cycloalkanes

Answer 4

functional group isomer of alkene

Question 5

what is the shape of an alkane

Answer 5

tetrahedral shape

Question 6

bond angle of alkanes

Answer 6

109.5

Question 7

isomerism in alkanes

Answer 7

only can possess chain isomers

Question 8

physical properties of alkanes

Answer 8

at room temp:
short alkanes <5 are gases
C5-C17 are liquids
longer carbon chains are waxy solids
non polar because the difference in electronegativity is very small
only VDW forces present
strength of VDWs increases as mr of the molecule increases
so bp and mp increase with mr

Question 9

branched alkanes

Answer 9

chain isomers
have lower melting and boiling points than straight chains with the same number of carbon atoms
smaller surface area in contact with each other
decreases strength of VDW forces
as less packed together
less energy needed to overcome the force

Question 10

solubility of alkanes

Answer 10

insoluble in water
water held together by strong hydrogen bonds, stronger than VDW forces
are soluble in other non - polar liquids

Question 11

how alkanes react

Answer 11

relatively unreactive
dont react with bases, acids, oxidising agents, reducing agents
do burn and will react with halogens under suitable conditions
bur n oxygen (plentiful supply) to form carbon dioxide and water

Question 12

where do we get organic chemicals from

Answer 12

crude oil
mixture containing mainly alkane hydrocarbons, both branched and unbranched that can be seperated via fractional distilation
dark yellow to black sticky viscous liquid

Question 13

how was crude oil made

Answer 13

also known as petroleum
formed from the remains of plants and animals which over millions of years became covered in mud , silt and sand
high pressures and temperatures changes allow all of these to slowly transform into oil

Question 14

steps of fractional distilation

Answer 14

crude oil is heated until it vaporizes
vapor and liquid passes into the fractionating column
fractionating column is cooler at the top and hotter at the bottom (negative temperature gradient)
as vapour rises up the column it cools and condenses into a liquid at their boiling point
fractions with higher boiling points condense at the bottom
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Question 15

what forces are broken during fractional distilation

Answer 15

no covalent bonds within molecules are broken
VDW forces between molecules are broken during vaporisation and reform upon condensing