Study of carbon compounds extracted from living organisms
Hydrocarbon
Class of organic compounds containing carbon & hydrogen only - covalently bonded
Types of hydrocarbons
Alkanes -> saturated hydrocarbons
Alkenes -> unsaturated hydrocarbons
Alkanes
Saturated hydrocarbons
Family of organic compounds in which the carbon atoms are single bonded
Functional group of alkanes
[C-C] singlecovalent bonds between carbon atoms
Homologous series
Family of organic compounds with same functionalgroup = same chemicalproperties, same generalformula, difference between 2 successive members are constant
Chemistry of alkanes
Only undergo substitutionreaction where Hydrogen replaced by monovalent atom in presence of light
Organic solvents
CHCl3 (chloroform)
CCl4 (carbon tetrachloride)
are volatile, have lowboilingpoint and are flammable
Alkanes
Burn in excess oxygen to give CO2 & H2O
Used as fuels
main constituent of natural gas is methane
Alkenes
Unsaturated hydrocarbons, organic compounds with a double covalent bond between carbon atoms
general formula -> [ Cn H2n ]
functional group -> c double bond c
Alkenes
Form homologous series
Undergo addition reactions
have same generalformula
have same functional group so have same chemicalproperties
Addition reactions of alkenes
2 monovalent atoms (radicals) are added to 2 adjacent carbon carrying the double bond which will break down to give a singlebond, forming saturated compound
Addition reactions of alkenes
Hydrogenation - in presence of nickelcatalyst and heat
alkene + hydrogen -> alkane
Halogenation
Hydration of alkenes
Alkene + Steam -> Alkanol, in presence of phosphoric or tungesticacid + heat and pressure
Alkanes undergo substitution which give 2 products, alkenes undergo addition which gives only 1 product
Test for unsaturation (presence of double bond)
Using aqueous bromine/bromine dissolved in CCl4 (orange) - alkane nochange, alkene decolourisation
Using acidified potassium manganate VII (purple) - alkane nochange, alkene decolourisation
Alkenes burn in good supply of oxygen to give CO2 & H2O and a large amount of heat, so they can be used as fuels
Isomers
Organic compounds with same molecularformula & different structuralformula
Crude oil (petroleum)
Complex mixture of saturatedhydrocarbons (alkanes) of similar boilingpoints, can be separated by fractional distillation but each section is still a mixture of alkanes
Products of fractional distillation of crude oil
Refinery gas - heatingandcooking
Petrol - fuelforcars
Naphtha - chemicals
Kerosene - jetfuel and used in stoves
Diesel oil - fuelfordieselengines
Fueloil - fuelforships and home heating systems
Lubricating oil - lubricants, waxes and polishes
Bitumen - roadsandroofs
Cracking
Breakdown of long chain alkanes to small chain alkanes to obtain more petrol
Cracking
Thermal cracking (high temp and pressure)
Catalytic cracking (in presence of catalyst)
Cracking of alkanes can produce alkenes & hydrogen making it an industrial process to prepare hydrogen like electrolysis
Alcohols (alkanols)
Homologous series of compounds of alkanes in which a hydrogen atom is replaced by an OH group
General formula (alcohols)
CnH2n+1OH or CnH2n+2O
Industrial preparation of ethanol
1. Catalytic hydration of ethene gas
2. Fermentation of sugar in presence of yeast
Fermentation
Max ethanol concentration 15%, if exceeded yeast will die
If 100% ethanol needed, fractionaldistillation is used
Optimum temp 35-40°C
Ethanol can oxidise to ethanoicacid if air enters apparatus
what is seen during fermentation? - bubblesofCO2
- frothisobtained
Fermentation is a process of biotechnology, using micro-organisms in production of compounds
Alcohols
undergo oxidation to give correspondingacid. slow when done in air and can be sped up by oxidising agents such as potassium manganate VII and potassium dichromate VI
alkanols are reducing agents
Alkanol + 2 oxygen -> Alkanoic acid (oxygen given by oxidising agent)
Burn to give clean flame in exothermic reaction
Uses of ethanol
Alcoholicdrinks
Solvent
Fuel
Carboxylic acids (alkanoic acids)
Compounds with a carboxyl functional group [-C(=O)OH]
General formula (carboxylic acids)
CnH2nO2 or CnH2n+1COOH
Preparation of ethanoic acid
Oxidation of ethanol by oxidising agent or bacterial oxidation
Carboxylic acids
Weak acids, partially ionise in water
Can react with bases & carbonates
Esterification reaction
Organic acid + Alcohol -> Ester + Water, using sulfuric acid as catalyst
Esters
Have a fruity smell, used for flavouring food & perfumes
Dehydration of ethanol
Ethanol -> Ethene, using concentratedH2SO4 (sulfuric acid) or Al2O3 & high temp or pumice stone & high temp
Formation of alkyl
Alkane - hydrogen -> alkyl
for alkanes to react with bromine it should be used as liquid Br2 without dissolving in solvent and reaction must be in presenceoflight
ethene is not used as fuel because it is used for manufacturing some industrial products like polyethene (plastic) and ethanol