hydrocarbons - organic chemistry

Question 1

what is a hydrocarbon?

Answer 1

A hydrocarbon is a compound that is made out of only hydrogen atoms and carbon atoms.

Question 2

what is crude oil

Answer 2

crude oil is a mixture of hydrocarbons

Question 3

whats a functional group

Answer 3

A functional group is defined as a particular group of atoms which are responsible for how the molecule reacts

Question 4

what is an alkane

Answer 4

The alkanes are a homologous series of hydrocarbons. A compound that contains hydrogen and carbon only.. This means that they have similar chemical properties to each other and they have trends in physical properties. For example, as the chain length increases, their boiling point increases.

Question 5

whats a homologous series

Answer 5

Homologous series are families or groups of organic compounds that have similar features and chemical properties due to them having the same functional group.

Question 6

what is an alkene?

Answer 6

Alkenes are a homologous series of hydrocarbons that contain a carbon-carbon double bond

Question 7

how do you name alkanes

Answer 7

number of carbons:
1- meth
2 - eth
3 - prop
4 - but
5 - pent
6 - hex

number the carbons to give the branch the smallest number possible

the branch is named by taking the code (from above) and adding -yl.

example:

2 - methyl propane

Question 8

how do you name alkenes

Answer 8

5 - methyl - 2 - hexene

5-methyl:
methyl - branch length
5 - location of branch

2-hexene:
hexene - longest chain length
2 - location of double bond

double bond takes priority when minimising number (eg. 5-methyl-2-hexene instead of 2-methyl-5-hexene)

Question 9

what is the general formula for alkanes

Answer 9

C(n)H(2n+2)

Question 10

what is the general formula for alkenes

Answer 10

C(n)H(2n)

Question 11

what does it mean if a hydrocarbon is saturated?

Answer 11

hydrocarbons with only single bonds

Question 12

what is isomerism

Answer 12

Isomerism is the phenomenon in which more than one compounds have the same chemical formula but different chemical structures.

Question 13

how can bromine be used to distinguish between an alkane and an alkene?

Answer 13

bromine water will go colourless when mixed with an alkene

Question 14

what is the difference with melting and boiling points between a pure substance and a mixture

Answer 14

a pure substance has a fixed melting and boiling point

a mixture may melt or boil over a range of temperatures

Question 15

what is the industrial process used to separate crude oil into fractions and how?

Answer 15

it is called fractional distillation

During the fractional distillation of crude oil:

heated crude oil enters a tall
fractionating column
, which is hot at the bottom and gets cooler towards the top

vapours
from the oil rise through the column
vapours
condense
when they become cool enough
liquids are led out of the column at different heights
Small hydrocarbon molecules have weak
intermolecular forces
, so they have low boiling points. They do not condense, but leave the column as gases. Long hydrocarbon molecules have stronger intermolecular forces, so they have high boiling points.

Question 16

what are the names and uses of the main fractions obtained from crude oil?

Answer 16

refinery gases - bottled gas (30 degrees, black/dark brown)
gasoline - fuel for car engines (100-150 degrees, transparent yellowish)
kerosene - fuel for aircraft and stoves (200-300 degrees, pale, yellow or colourless)
diesel - fuel for road vehicles and trains (200-300 degrees)
fuel oil - fuel for ships, heating and power stations (350-450 degrees, dark brown)
bitumen - road surface and roofing (above 500, black)

gets darker as boiling point increases. viscosity increases as well.

Question 17

what is a fuel

Answer 17

a substance that, when burned, releases energy

Question 18

what is complete and incomplete combustion

Answer 18

In complete combustion, there is a sufficient supply of oxygen which is able to react with the burning hydrocarbon allowing the reaction products H2O and CO2 to be formed. In incomplete combustion there is a lack of oxygen so when heat is applied carbon monoxide is released.

possible products of incomplete:
- carbon monoxide
- carbon particles
- water

possible products of complete:
- water vapour
- carbon dioxide

Question 19

why is carbon monoxide poisonous?

Answer 19

Carbon monoxide is a poisonous gas which binds to haemoglobin. in your red blood cells, preventing them from carrying oxygen to the cells in your body.

Question 20

what happens in car engines to nitrogen and oxygen?

Answer 20

nitrogen and oxygen in the air react, forming oxides of nitrogen due to the high temperature reached

Question 21

what can happen in the combustion of some impurities in hydrocarbon fuels

Answer 21

the formation of sulfur dioxide of nitrogen oxide. these contribute to acid rain

Question 22

what is cracking

Answer 22

long-chain alkanes are converted to alkenes and shorter-chain alkanes by catalytic cracking (using silica or alumina as the catalyst and a temperature in the range of 600-700 degrees)

Question 23

why is cracking necessary

Answer 23

helps deal with the balance between supple and demand for different fractions

Question 24

what happens when alkenes react with bromine

Answer 24

they produce dibromoalkanes. For example, ethene reacts with bromine to produce dibromoethane. The double bond between the two carbon atoms breaks and the bond between the bromine atoms in the bromine molecule breaks.

Question 25

how is an addition polymer formed?

Answer 25

it is formed by joining up many small molecules called monomers

Question 26

what are some problems in the disposal of addition polymers?

Answer 26

they have an inertness and inability to biodegrade so end up in landfill or in the sea, damaging wildlife and taking up valuable land

the production of toxic gases when they are burned can cause health risks to wildlife and humans

Question 27

what is a mono-substitution reaction with alkanes

Answer 27

if an alkane reacts with a halogen (eg. chlorine, bromine) in the presence of ultraviolet radiation, one of the hydrogens is replaced by one of the halogens.

example:

CH4 + Cl2 –> CH3Cl + HCl