unit7) Organic chemistry

• What are hydrocarbons

  Compounds that only contain carbon and hydrogen
• What are alkanes

  saturated hydrocarbons
• List the 1st 4 alkanes

  Methane, ethane, propane, butane

  
• Alkanes: saturated or unsaturated


  saturated
• Formula of methane

  CH4
• Formula of ethane

  C2H6
• Formula of propane

  C3H8
• Formula of butane

  C4H10
• General formula for alkanes

  CnH2n+2
• Properties of short chain hydrocarbons

  Low boiling point, high volatility, low viscosity, high flammability
• Properties of long chain hydrocarbons

  higher boiling point, lower volatility, high viscosity, lower flammability
• Equation for complete combustion of a hydrocarbon

  Hydrogen + oxygen -> carbon dioxide + water vapour
• What is crude oil?

  Mixture of hydrocarbons, formed from remains of plants/animals/plankton over millions of years.
• Disadvantages of crude oil

  Finite as it takes so long to form, once used it cannot be replaced
• What is fractional distillation used for (crude oil)

  Splitting crude oil into separate hydrocarbon fractions
• How does fractional distillation work?

  -crude oil is evaporated. Gases enter fractionating column-there is a temp gradient in a fractionating column. Hot at bottom and cooler at top-shorter hydrocarbons have lower bpts so they condense further up the column and vice versaYou end up with the crude oil separated into different fractions. Each fraction contains a mixture of hydrocarbons that contain a similar number of carbon atoms so have similar boiling points.

  
• Uses of crude oil

  Fuels: diesel, kerosene, heavy fuel oil, petroleum. petrochemical industry (feedstock),
• What's cracking

  Splitting up long chain hydrocarbons
• Why is cracking useful

  Because long chain alkanes are not as useful as shorter alkanes which can be used as fuelsBecause cracking produces alkenes as well as alkanes. Alkenes are a starting material for other compounds and polymers.
• What type of reaction is cracking

  Thermal decomposition
• Steps of catalytic cracking

  1)heat long chain hydrocarbons to vaporise them 2)vapour is passed over a hot powdered aluminium oxide catalyst 3)long chain molecules split apart on the surface of the specks of catalyst
• Steps of steam cracking

  1)heat long chain hydrocarbons to vaporise them

  2)mix them with steam

  3) heat to high temp
• What are alkenes


  unsaturated hydrocarbons (double bond c=c)
• Reactivity of alkenes

  more reactive than alkanes due to double bond
• Alkenes; saturated or unsaturated?

  unsaturated
• Name the 1st four alkenes and their formulas

  Ethene (e2h4), propene (c3h6), butene (c4h8), pentene (c5h10)

  
• Incomplete combustion


  The process by which an alkene burns in insufficient oxygen to produce some carbon monoxide (CO).
• Equation for incomplete combustion of Alkenes

  Alkene + oxygen -> carbon + carbon monoxide + carbon dioxide + water
• Functional group of alkenes

  C=c
• How do alkenes react?

  Addition reactions (carbon double bond opens)
• What is hydrogenation?

  Hydrogen reacting with an alkene by addition reactions
• What happens in hydrogenation

  Hydrogen reacts with double bonded carbons to open the double bond and form the equivalent saturated alkane. Reacted in presence of catalyst

  
• How to form alcohol from alkenes

  • react alkene with steam in the presence of a catalyst
  • water added across double bond. Alcohol formedE.g. butene + water (with acid catalyst)-> butanol

  
• How is ethanol produced from ethene?

  -eg: ethanol made by mixing ethene with steam and passing over catalyst-after reaction: passed from reactor to condenser.-Ethanol and water have a higher bpt than ethene. Both condense while un reacted ethene is recycled back into reactor.-alcohol purified from mixture by fractional distillation
• Addition reaction of alkenes with halogens

  C=C bond becomes opened and each C bonds to a halogen atom
• How to test for alkenes?

  Bromine water turns from orange to colourless if unsaturated alkene is present
• Bromine + ethene

  Dibromoethane

  
• What are polymers

  long chains of monomers
• What is polymerisation?

  Process by which small molecules called monomers join together to form polymers
• Conditions for polymerisation

  High pressure and a catalyst