hydrocarbons

• what is a homologous series ?

  A series of organic compounds with the same general formula and similar chemical properties as they have the same functional group
• what is the functional group of alcohols ?

  hydroxyl group (-OH)
• what is the functional group of carboxylic acids ?

  carboxyl group (-COOH)
• what are the characteristics of a homologous series ?

  • have the same functional group
  • have similar chemical properties
  • each member of the series differs from the next by an additional -CH2- unit
  • is a gradual change in their physical properties as we go down the series from one member to the next
• what is the prefix when n=1?

  meth
• what is the prefix when n=2 ?

  eth
• what is the prefix when n=3 ?

  prop
• what is the prefix when n=4 ?

  but
• what is the prefix when n=5 ?

  pent
• what are alkanes ?

  hydrocarbons that contain only carbon- carbon single bonds and carbon- hydrogen bonds
• what is the general formula of alkanes ?

  CnH2n+2
• alkanes are saturated as they contain only carbon- carbon single bonds
• are alkanes reactive or unreactive ?

  unreactive
• why are alkanes unreactive ?

  they are saturated, with each carbon atom being covalently bonded to 4 other atoms so no new atoms can be added to it anymore
• what is the solubility of alkanes ?

  • are insoluble in water
  • are soluble in most organic solvents like tetrachloromethane
  • liquid alkanes are often used as solvents for other organic compounds
• what happens when alkanes/ alkenes burn in excess oxygen ?

  complete combustion takes place to produce carbon dioxide and water
• what happens when alkanes/ alkenes burn in insufficient oxygen ?

  incomplete combustion takes place to produce carbon monoxide, carbon dioxide, carbon and water
• what reaction takes place when alkanes react with halogens ?

  substitution reaction
• what are the products of the reaction where a hydrogen atom is substituted by a chlorine atom ?

  chloromethane and hydrogen chloride
• what are alkenes ?

  hydrocarbons that contain carbon- carbon double bonds
• what is the general formula of alkenes ?

  CnH2n
• what is the solubility of alkenes ?

  • insoluble in water
  • soluble in most organic solvents like hexane and tetrachloromethane
• alkenes are unsaturated as they contain carbon- carbon double bonds
• are alkenes reactive or unreactive ?

  reactive as each carbon atom is covalently bonded to 3 other atoms only so a new atom can be added to it
• what is the difference in the flames of alkanes and alkenes when they burn ?

  alkenes burn with sootier flames than alkanes because the percentage of carbon by mass in alkenes is higher than that in alkanes for the same number of carbon atoms present
• what are the conditions for hydrogenation ?

  150 degrees, nickel catalyst
• write down the word equation of hydrogenation ?

  alkene + hydrogen -> alkane
• what is observed when alkenes are reacted with bromine ?

  the solution decolourises
• what is observed when alkanes are reacted with bromine ?

  no observations
• what are the conditions of hydration ?

  300 degrees, 60 atm and phosphoric (V) acid catalyst
• what is cracking ?

  it is the process where larger hydrocarbon molecules, usually alkanes, are broken down into smaller hydrocarbon molecules
• what are the conditions of catalytic cracking ?

  500 to 700 degrees, 1 atm, aluminium oxide or silicon dioxide catalyst
• what is the importance of cracking ?

  • converts the less useful components, long- chain alkanes, of crude oil into shorter- chain alkenes or shorter- chain alkanes
  • to match the demand of shorter- chain alkanes and alkenes for fuel and industrial processes
  • produces hydrogen as a byproduct which is important for industrial reactions like production of ammonia
• what are isomers ?

  compounds that have the same molecular formula but different structural formula
• how can we test for unsaturated hydrocarbons ?

  bromination, shaking aqueous bromine with the hydrocarbon
• how do we classify polyunsaturated fats ?

  fats that contain hydrocarbon chains with 2 or more carbon- carbon double bonds in each chain
• how can we manufacture margarine from vegetable oils ?

  through hydrogenation of a part of a vegetable oil molecule
• explain why margarine is solid while vegetable oil is liquid ?

  as more hydrogen molecules are added into the oil molecules, there are fewer carbon- carbon double bonds and the melting point of the oil increases
• is margarine saturated or unsaturated ?

  saturated
• is vegetable oil saturated or unsaturated ?

  unsaturated