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PHS CHEMISTRY 1 2018 - ORGANIC CHEMISTRY (FUELS (The fossil fuels are coal…
PHS CHEMISTRY 1 2018 - ORGANIC CHEMISTRY
NAMES OF COMPOUNDS
Methane -
Ethane -
Ethene -
Ethanol -
Ethanoic acid -
Alk
ane
- single bonds
Alk
ene
double bonds
Alcohols -
ol
have an OH functional group
Carboxylic acids -
oic
have COOH functional group
FUELS
The
fossil fuels
are
coal
,
petroleum
(crude oil) and
natural gas
Petroleum
is formed from the remains of dead organisms that fell to the ocean floor and were buried under thick sediment. High pressures slowly converted them to petroleum, over millions of years. It is a mixture of hydrocarbons and it has useful separation into fractions by fractional distillation.
Coal
is the remains of lush vegetation that grew in ancient swamps. The dead vegetation was buried under thick sediment. Pressure and heat slowly converted it to coal, over millions of years.
Natural Gas
is mainly
methane
. It is often found with petroleum. It is formed in the same way. But high temperatures and high pressures caused the compounds to break down into gas.
Fractional Distillation
eg.
GASOLINE
(petrol) - used as fuel for cars
PARAFFIN
(kerosene) - fuel for aircraft, oil stoves and lamps
DIESEL OIL
(gas oil) - fuel for diesel engines
LUBRICATING FRACTION
- oil for car engines and machinery
BITUMEN
- for making roads
HOMOLOGOUS SERIES
A
homologous
series is a 'family' of compounds with similar chemical properties due to similar structures.
⟶ This is because they have the same
functional group
⟶ a functional group is a
part of a molecule that largely dictates how the molecule will react
⟶ eg. all alkanes have similar reactions because they all have the same functional group, the C - C bond
ALKANES
GENERAL FORMULA
is CnH2n+2
only
single bonds
present in chain
alkanes are
saturated compounds
as the maximum number of hydrogen atoms per carbon is present
end with
'ane'
generally, alkanes are quite unreactive
although, alkanes do burn well in a good supply of oxygen - forming carbon dioxide and water vapour, and giving off heat
⟶ they are used as fuels
ALKENES
GENERAL FORMULA
is CnH2n
chains with
double bonds
form alkenes
because they contain
double bonds
, they are
unsaturated
end with
'ene'
TEST FOR UNSATURATION
bromine water
can be used to test whether a hydrocarbon is unsaturated
⟶ the solution is orange, and if a C = C double bond is present, a reaction takes place and the colour disappears
ethene with bromine water
because alkenes are more reactive than alkanes, they can add on hydrogen again
⟶ eg. ethene can add on hydrogen again to form ethane
ethene with hydrogen
alkenes can also add water (as steam) to form an alcohol
ethene with steam
These reactions are called
addition reactions
. An addition reaction turns an
unsaturated alkene into a saturated compound
POLYMERISATION
Alkene molecules undergo a very useful addition reaction, where they add on to each other to form compounds with very long carbon chains. The alkene molecules are called
monomers
and the long-chain compounds that form are called
polymers
.
The product is
poly(ethene)
polymerisation
CRACKING
The alkenes are made from alkanes by cracking. For example, ethene is formed by cracking ethane. Hydrogen is also produced
cracking
ALCOHOLS
GENERAL FORMULA
is CnH2n+1OH
the OH functional group means they will all react in a similar way
ethanol is a good solvent. It dissolves many substances that do not dissolve in water
it evaporates easily - it is volatile. That makes it a suitable solvent to use in glues, printing inks and perfumes
it burns readily in oxygen, and the reaction gives out plenty of energy, as heat, therefore it is used as a fuel
ethanol is also a constituent of wine and beer
CARBOXYLIC ACID
GENERAL FORMULA
is CnH2nO2
the functional group COOH is also called the
carboxyl group
Ethanoic acid is made by oxidising ethanol. The oxidation can be carried out in two ways:
FERMENTATION
- THE BIOLOGICAL WAY
When ethanol is left standing in air, bacteria bring about its oxidation to ethanoic acid. (
acid fermentation
)
Acid fermentation is used to make vinegar. The vinegar starts as foods such as apples, rice and honey, which are first fermented to give ethanol
USING AN OXIDISING AGENT
- THE CHEMICAL WAY
Ethanol is oxidised much faster by warming it with potassium manganate (VII), in the presence of acid. The manganate ions are themselves reduced to Mn 2+ ions, with a colour change. The acid provides the H + for the reaction:
purple---------------------------------------colourless
MnO4 (-) + 8H (+) + 5e (-) ⟶ Mn (2+) + 4H2O
REACTIONS
carboxylic acids react with metals to form a salt and hydrogen
they react with alkali (neutralisation) to form a salt and water
carboxylic acids react with alcohols to give compounds called
esters
.
a solution of ethanoic acid is
acidic
because it contains H+ ions. They are present because some ethanoic molecules
dissociate
in water - it is a
weak acid
Esters
are two hydrocarbon chains joined by an oxygen (and give a product of water) eg:
formation of propyl ethanote (an ester)
two molecules join together to make a larger molecule, with the loss of a small molecule, water. This is a
condensation reaction
.
the negative ion after the proton has left gets an
'anoate'
ending
the reactions are reversible and eg. sulfuric acid can act as a catalyst
