1.5- Organic chemistry Flashcards
Define saturated and unsaturated?
Saturated: contains single carbon-carbon bonds only
Unsaturated: contains a carbon-carbon double bond
Define hydrocarbon?
Compound consisting of hydrogen and carbon only
Define petroleum fraction?
Mixture of hydrocarbons with a similar chain length and boiling point range
Define molecular formula?
Formula which shows the actual number of each type of atom
Define empirical formula?
Shows the simplest ratio of whole number of atoms of each element in the compound
Define general formula?
The algebraic formula for a homologous series e.g. CnH2n
Define displayed formula?
Show all the covalent bonds present in a molecule
Define homologous series?
Families of organic compounds with the same functional group and the same general formula
They show a gradual change in physical properties like boiling point
Each member differs by CH2 from the last
Same chemical properties
Define functional group?
An atom or group of atoms which when present in different molecules causes them to have similar properties
General formulae for alkanes, alkanes and haloalkanes?
Alkane- CnH2n+2
Alkene- CnH2n
Haloalkane- CnH2n+1X
What are structural isomers?
Compounds with the same molecular formulae but different structural formulae
Define chain isomerism?
Compounds with the same molecular formula but different structures of the carbon skeleton
Define positional isomerism?
Compounds with the same molecular formula but different structures due to different positions of the same functional group on the carbon skeleton
Define functional group isomerism?
Compounds with the same molecular formula but different structures due to atoms arranged to give different functional groups
What is petroleum/crude oil?
Mixture consisting of mainly alkane hydrocarbons
Explain the steps of fractional distillation?
- Crude oil is preheated and vaporised and passed into the column
- The fractions condense at different heights
- The temperature of the column decreases upwards
- The separation depends on the boiling point
- Boiling point depends on the size of molecules
- The larger the molecules the larger the van der Waals forces
- Similar molecules condense together
- small molecules condense at the top at lower temperatures and big molecules condense at the bottom at higher temperatures
What is vacuum distillation?
It allows heavier fractions to be further separated without high temperatures which could break them down
Heavy residues from the fractionating column are distilled again under a vacuum
Lowering the pressure over a liquid will lower its boiling point
What is cracking and what does it produce?
Conversion of large hydrocarbons into smaller molecules by breaking of C-C bonds
High Mr alkanes –> smaller Mr alkanes+ alkenes + (hydrogen)
What are the economic reasons for cracking?
Shorter chain length petroleum fractions are more in demand
To make use of excess larger hydrocarbons
Products of cracking are more valuable than the starting materials
What is thermal cracking?
High pressure (7000kPa) and high temperature (400-900°C)
Produces mostly alkenes (ethene used to make polythene and ethanol) and sometimes hydrogen (haber process and margarine manufacture)
What is catalytic cracking?
Low pressure and high temperature (450°C) and zeolite catalyst
Produces branched and cyclic alkanes and aromatic hydrocarbons
Used to make motor fuels
What is a fuel?
Something that releases energy when burnt
What is complete and incomplete combustion?
Complete: in excess oxygen alkanes will burn in complete combustion producing CO2 and H2O
Incomplete: If there is a limited amount of oxygen then incomplete combustion occurs producing CO (toxic) and/or C (sooty flame)
How is SO2 produced from burning fuels and what does it cause?
Sulphur impurities found in the petroleum fraction
Cause acid rain
How can SO2 be removed?
Flue gas desulphurisation- waste gases pass through a scrubber containing basic calcium oxide which reacts with the acidic SO2 in a neutralisation reaction to produce Calcium sulphite
How are nitrogen oxides produced and what do they cause?
Formed when N2 in the air reacts at high temperatures and spark in the engine
NO is toxic
NO2 causes acid rain
What does CO2 contribute towards?
Global warming
What do unburnt hydrocarbons cause?
Formation of smog
What does soot cause?
Global dimming and respiratory problems
What are catalytic converters?
Remove CO, NOx and unburnt hydrocarbons turning them into harmless CO2, N2 and H2O
Have ceramic honeycomb coated with a thin layer of catalyst metals platinum, palladium, rhodium to give a large surface area
