C6.2 Flashcards
Hydrocarbons
Compounds that only contain hydrogen and carbon atoms
What are alkanes
Homologous hydrocarbons
Why do alkanes from a homologous series
They have common features :
-same general formula
-carbon atoms are joined together by single covalent bonds
All alkanes are SATURATED
Are alkanes saturated or non saturated
Saturated
General formula for alkanes
CnH2n+2
Each successive member differs by a CH2 group
How do alkanes react
Through combustion
If there is a plentiful supply of oxygen or air , complete combustion happens
Are the atoms oxidised or reduced during combustion
Carbon atoms are oxidised , forming carbon dioxide
Hydrogen atoms are oxidised , forming water
What happens if there is a poor supple of oxygen or air during combustion
Incomplete combustion happens instead
Water is formed , but carbon is only oxidised to carbon monoxide , CO
Some carbon atoms may not be oxidised if there is a further lack in oxygen or air , forming C
Why is CO bad
It is a toxic gas and can cause suffocation
Crude oil
A fossil fuel formed from the remains of marine organisms that died millions of years ago , turning into crude oil due to chemical reactions
Finite resources
No longer being made or are being made extremely slowly , and is being used up faster than being formed
Features of a homologous series
Saturated - all atoms joined together by simple covalent bonds
Same general formula
All differ by CH2
What type of compounds are alkanes
Colourless , but have gradual physical property changes as the number of carbon atoms in the chain increase
Generally unreactive
CH4
Methane
C2H6
Ethane
C3H8
Propane
C4H10
Butane
Name the first four alkanes
Methane , ethane , propane , butane
What are alkenes
Hydrocarbons that form a homologous series
What is the main difference between alkanes and alkenes
Alkene molecules contain a C=C double bond
This means that alkenes are unsaturated
General formula for alkenes
CnH2n
Functional group
An atom , or group of atoms , or type of bond in a molecule that uses responsible for the characteristic reactions of the substance
In alkenes , which bond allows the substance to undergo additional reactions
The C=C double bond
Addition reaction
An atom or group of atoms combines with a molecule to form a larger molecule , with no other
products formed
Basic test for unsaturation
Bromine reacts with alkenes but not alkanes . Bromine water is orange brown , but will turn colourless if an alkene is mixed with it . It remains orange brown if an alkane is added to it
Alkenes can also undergo addition reactions with hydrogen in the presence of
A nickel catalyst
The more carbon atoms there are in the alkane molecules
-the larger the molecules
-the stronger the intermolecular forces
-the higher the boiling point
How is crude oil made useful
It is made up of a mixture of hydrocarbons , mostly alkanes
They are separated using fractional distillation . This works well because each alkane has a different boiling point
Describe the process of fractional distillation - crude oil
-Crude oil is heated and it’s vapours are piped into the bottom of a fractionating column , which has a a temperature gradient ( hot at the bottom , cold at the top )
-Vapours cool as they rise through the column
-each fraction contains many substances with similar boiling points
Fraction
Separated parts of the crude oil
Which alkane has the highest boiling point
Bitumen , during fractional distillation it leaves at the bottom of the column and is in the solid state at room temperature
Which substances have the lowest boiling points during fractional distillation
Refinery gases - methane , ethane , propane , and butane have the lowest boiling points
They reach the top and leave the column without cooling enough to condense
The other substances
Are in liquid state at room temperature, they fall into trays and leave from the middle of the column
