C7-Organic Chemistry

• A hydrocarbon is a molecule made up of hydrogen and carbon atoms only.
• A homologous series is a group of molecules that have similar properties and all share a general formula
• Alkanes have a general formula of C$_n$H$_{2n+2}$
• Alkanes are saturated compounds, as they have a single covalent bond between each carbon atoms
• Methane is $CH_4$
• This is the displayed formula for methane

  
• Ethene is $H_2C_6$
• This is the displayed formula for ethene

  
• Propane is $H_3C_8$
• This is the displayed formula for propane

  
• Butane is $C_4H_{10}$
• This is the displayed formula for butane

  
• As the length of the hydrocarbon increases, the viscosity increases
• As the length of hydrocarbon increases, the flammability decreases
• As the length of hydrocarbons increases, the boiling point increases
• Complete combustion of a hydrocarbon :

  Hydrocarbon + Oxygen $\rightarrow$ Carbon Dioxide + Water
• Crude oil is a finite resource
• Crude oil is the remains of an ancient biomass consisting mainly of plankton that was buried in mud under high pressure
• Fractional distillation separates hydrocarbon :

  • Crude oil is heated until it becomes a gas and this is fed into the fractionating column
  • In the column there is a temperature gradient as hot at the bottom and cooler at the top
  • The longer hydrocarbon chains have high boiling points and condense back into liquids near the bottom of the column
  • The shorter hydrocarbon chains having low boiling point and leave the fractional column as a gas at the top
• Uses of products for fractional distillation ;

  • For fuel such as petrol, diesel oil and kerosene
  • For feedstock
  • For other useful materials such as solvents and lubricants(reduces friction)
• Cracking is the process of breaking up longer chain hydrocarbons into smaller, more useful ones
• The two methods of cracking are steam and catalytic cracking
• In catalytic cracking, the long chain hydrocarbons are vapourised and then mixed with a catalyst
• In steam cracking, the long chain hydrocarbons are vapourised and then mixed with steam at very high temperature
• Alkenes have a general formula of $C_nH_{2n}$
• Alkenes are unsaturated compounds, as they have a double covalent bond between each carbon atoms
• Alkanes are less reactive than alkenes
• Ethene is $C_2H_4$
• This is the displayed formula for ethene

  
• Propene is $C_3H_6$
• This is the displayed formula for propene

  
• Butene is $C_4H_8$
• Pentene is $C_5H_{10}\$
• This is the displayed formula for pentene

  
• Complete combustion of alkenes :

  Alkene + Oxygen $\rightarrow$ Carbon Monoxide + Carbon Dioxide + Water
• Incomplete combustion of alkenes result in a smoky yellow flame
• Alkenes reacting with hydrogen :

  • The two hydrogen molecule are added across the carbon double bond to form an alkane
• Alkenes reacting with steam :

  • Alkenes react with steam at high temperatures and pressure in the presence of a catalyst to form alcohols
• Alkenes reacting with halogens :

  • The two atoms from the halogen molecule are added across the carbon double bond
• To test for alkenes, bromine water is used