Organic Chemistry Flashcards
What are the columns in the fractional distillation of petroleum and their uses?
LPG (Liquefied Petroleum Gas) - Fuel for cooking
Gasoline - Fuel for cars
Naphtha - Chemical feedstock, detergents, plastics
Kerosene - Lamps, fuel for aircraft
Diesel - Fuel for diesel engines
Lubricating oils - Lubricants, polishes & waxes
Bitumen - Road surfaces
(Petroleum is pumped in)
What happens as the hydrocarbon molecules increase? (Top to bottom down column)
Boiling points increases
- Intermolecular forces between molecules increases as size of molecule increases
- More energy required to overcome IMF
Higher viscosity
- IMF between molecules increases, as size of molecule increases
- Forces are difficult to overcome, become waxier and thicker, do not flow easily
Less flammable
- Percentage by mass of carbon increases, as size and mass of molecules increases, hydrocarbons become less flammable
Low volatility
- IMF between molecules increase when size of molecules increases, more heat required to break forces to change their physical state
What are alkanes?
- C(n)H(2n+2)
- Obtained directly from fractional distillation of petroleum
- Contains carbon-carbon single bond (no functional group)
- Saturated hydrocarbons
What are the reactions with alkanes?
COMBUSTION (exothermic, blue/clean flame)
Alkane + oxygen -> water + carbon dioxide
INCOMPLETE COMBUSTION (yellow smoky flame)
Alkane + oxygen -> carbon monoxide + water
OR
Alkane + oxygen -> soot (carbon) + water
(soot, carbon monoxide & water as waste products)
SUBSTITUTION
- Presence of light as catalyst
- Hydrogen atom is displaced by a molecules of halogen gas
CH4 + Cl2 -> CH3Cl + HCl
Ch3Cl + Cl2 -> CH2Cl2 + HCl
Cracking
- Breaking of large alkane molecules tp produce smaller useful molecules
- Smaller alkanes, burn easier
1. Large alkane -> smaller alkane + alkenes
2. Large alkene -> alkenes + hydrogen
What are alkenes?
- C(n)H(2n)
- Functional group of carbon-carbon double bond (C=C)
- Unsaturated hydrocarbon
Alkenes are generally more reactive as they have a carbon-carbon double bond, bonded to 3 other atoms respectively, new atom can be added when bond is broken
What are the reactions with alkenes
COMBUSTION (sootier flames than alkanes, higher carbon % by mass)
Alkene + oxygen -> water + carbon dioxide
ADDITION (HYDROGENATION) (nickel catalyst, 200°C)
Alkene + hydrogen -> alkane
HYDRATION (conc. phosphoric acid, 300°C)
Alkene + steam -> alcohol
BROMINATION (Distinguish alkane from alkene)
Alkene + Bromine -> 1,2-dibromoalkane
Dibromoalkane is colourless,
Alkane: BROWN BROWN
Alkene: BROWN COLOURLESS
What are alcohols
- C(n)H(2n+1)OH
- Functional group of hydroxyl -O-H
- Colourless neutral liquids, low bp
What are the production methods and reactions with alcohol
FERMENTATION (anaerobic respiration of yeast, at optimum temp 40°)
Glucose/sugar -> ethanol + carbon dioxide
Ethanol from yeast only gives a low concentration and must be separated from sugar by fractional distillation
HYDRATION (conc. phosphoric acid, 300°C)
Alkene + steam -> alcohol
COMBUSTION clean/blue flame
Alcohol + oxygen -> water + carbon dioxide
OXIDATION (by bacteria with oxygen or reducing agent KMnO4
Alcohol + oxygen -> carboxylic acid + water
C3H7OH + O2 -> C2H5COOH(aq) + H2O
Alcohol tastes sour after left in the air due to oxidation in carboxylic acid
What are carboxylic acids
- C(n-1)H(2n-1)COOH
O
II - Functional group carboxyl - C-O-H
What are the reactions with carboxylic acids (weak acid)
Partially ionises H+ ions when dissolved in water (for salt, metal is at the back, H is replaced)
Acid + metal -> salt + hydrogen
Acid + metal carbonate -> salt + carbon dioxide + water
Acid + alkali -> salt + water
ESTERIFICATION
Carboxylic acid + alcohol -> ester +water
ethanoic acid + propanol -> propyl ethanoate
Conditions for combustion
Complete combustion -> CO2 & H2O
Incomplete gives CO
Alkenes have a higher % of C compared to alkanes (C:H ratio)
Alkenes burn brighter, smokier flame, produces soot
Conditions for hydrogenation
H2 200°C Nickel catalyst (normal pressure)
(Form margarine)
Cn+H2 -> CnH2n+2 (alkane)
Conditions for hydration
Steam 300°C 65atm Phosphoric acid catalyst
alkene -> alcohol
Conditions for bromination
Aqueous bromine, rtp, Reddish brown Br decolourises RAPIDLY
Conditions for cracking
High temp, 600°C Al2O3/SiO2 catalyst
Produces shorter more useful alkenes & alkanes, & H2 used in Haber Process
