Organic chemistry Flashcards
(27 cards)
homologous series
- Family of similar compounds
- similar chemical properties due to the same functional group.
Functional group
- set of atoms which dictate the chemical properties of that compound.
- compounds that share same functional group, share similar chemical properties.
Alkane
C - C
- ane
Alkene
C = C
-ene
Alcohol
C - O - H
-anol
Carboxylic acid
C = O - O - H
-anoic acid
Ester
C = O - O - C
-yl -anoate
characteristics of a homologous series
All members of the series can be presented by the same general formula
Consecutive members of the series differ by CH2
They have similar chemical properties because they have the same functional group
Their physical properties change in a predictable way
Alkane General formula
CnH2n+2
Saturated Carbons
Alkanes are hydrocarbons (compounds that contain only carbon and hydrogen).
Since no more atoms can add onto the molecule they are described as saturated hydrocarbons.
They are generally unreactive except for combustion and substitution reaction.
Alkane Combustion
The complete combustion of an alkane gives carbon dioxide and water
The incomplete combustion of an alkane gives carbon monoxide and water
Alkane Substitution
Alkanes react with chlorine in bright light to give a mixture of chloroalkanes.
One hydrogen atom is substituted by one chlorine atom.
Cl- Chloroalkane
Cl2- dichloroalkane
Cl3 - trichloroalkane
Cl4 - tetrachloroalkane
General formula Alkene
CnH2n
Unsaturated hydrocarbons
Alkenes contain carbon double bonds (C=C). Unlike alkanes, alkenes can undergo addition reactions due to the C=C double bond, and are therefore called unsaturated hydrocarbons.
Addition Reaction
The C=C double bond in alkenes can be broken to “add” molecules onto the compound. There will therefore two reactants but only one product formed.
Alkenes can undergo addition reactions with bromine, hydrogen, and steam.
Test for Alkene
Aqueous bromine undergoes addition reactions with alkenes. As a result, the original brown colour of aqueous bromine will turn colourless in the presence of alkenes.
Dibromoethane
Hydrogen
Hydrogen reacts with alkenes to produce alkanes.
The conditions required for this reaction are:
- Temperature 150 degrees
- Nickel catalyst
Water (steam)
Water can react with alkenes to make alcohols. This type of reaction is called hydration.
The conditions required for this reaction are:
- Temperature 300 degrees
- Pressure 60 atmospheres
- Phosphoric acid catalyst
Addition Polymerization
Polymerization is the formation of long chain molecules called polymers from a large number of monomer molecules.
General formula Alcohols
CnH2n+1OH
Ethanol manufacture
Ethanol can be manufactured by two methods:
- Catalytic hydration of ethene
- Fermentation
Hydration of Ethene
Water can react with alkenes to make alcohols. This type of reaction is called hydration.
The conditions required for this reaction are:
Temperature 300 degrees
Pressure 60 atmospheres
Phosphoric acid catalyst
The advantages of hydration (for ethanol manufacture) are
- No waste products
-Produces ethanol continuously
The disadvantages are
- Use of crude oil which is non-renewable
- Requires a lot of energy for high heat and pressures
Fermentation
Fermentation is the chemical breakdown of glucose by yeast (or other microorganisms). Carbon dioxide and ethanol is produced in the process and the reaction is catalysed by yeast enzymes.
yeast Glucose ———> Ethanol + Carbon dioxide
The advantages of fermentation
- Renewable (uses plants)
- Uses less energy (lower temperature & pressure)
The disadvantages are
- Slow, batch process i.e. needing new batch once yeast die
- Produces carbon dioxide as waste
Properties & uses of ethanol
Ethanol burns with blue flame. Combustion of ethanol will produce carbon dioxide and water.
Ethanol can be used:
- As a fuel (i.e. combusted)
as a solvent in perfume and food industries
- To make other organic chemicals such as esters
