Chemistry 7.2 (Alcohols, Carboxylic Acids and Esters)
- Created by: Becca.
- Created on: 21-06-16 11:33
Hydrocarbons
Made up only of carbons and hydrogens
Carbon can be many different structures: simple molecular eg.carbon dioxide, giant lattice eg.graphite/diamond
Hydrocarbons are fuels
Alkanes
(CnH2n+2)
Alkanes are hydrocarbons
Only has single C-C bonds, therefore alkanes are saturated compounds
Alkanes have covalent bonding therefore have strong intramolecular bonds, the larger the molecule to stronger the bonds (this makes them solids)
Properties: oily hydrocarbons don't mix with H2O /aqueous solutions, flammable (products are H2O and CO2)
Functional group: C-H
eg. ethane C2H6
Alkenes
(CnH2n)
Contain a double C=C bond, they are unsaturated compounds which makes it more reactive than alkanes
Functional group: C=C
Alcohols
(CnH2n+1OH)
Short chains have low boiling points due to weak intermolecular forces (long chainshave higher boiling points), however this is still higher than the corresponding alkane because the O-H strengthens the intermolecular bonds; short chains are also soluble
Flammable (products: carbon dioxide and water)
Functional group: O-H
Production of ethanol
Fermentation of sugar: C6H12O6 --> 2C2H5OH + 2CO2 ; glucose(maize/corn) --> impure ethanol + carbon dioxide.
Advantages: low temperature/pressure, renewable resource, carbon neutral. Disadvantages: low atom economy (51%), impure ethanol, feedstock takes up land which could be used for housing and food
Converting ethene: C2H4 + H2O --> C2H5OH ; crude oil + water --> ethanol.
Advantages: high atom economy (100%), 95% yeild, 96% pure ethanol. Disadvantages: high temperature/pressure, producing ethene requires energy, non-renewable source
Converting biomass: C6H12O6 --> 2C2H5OH + 2CO2 ; glucose(genetically modified e.coli bacteria) --> impure ethanol + carbon dioxide.
Advantages: carbon neutral, renewable resource, low temperature/pressure. Disadvantages: low atom economy (51%), impure ethanol, fossil fuels need to purify
Carboxylic acids
End in -COOH
Have unpleasant tastes and smells eg. rancid butter, sweaty socks, vinegar
eg. ethanoic acid CH3COOH
Carboxylic acids are weak because they are organic acids, ie. with carbon, so only partially ionise when put in water
Inorganic acids, ie. without carbon, are strong as the they give off all of the hydrogen ions/fully ionise when put in water
Acid + Metal → Salt + Hydrogen
Acid + Alkali → Salt + Water (+ Carbon dioxide, if a carbonate)
Carboxylic Acid + Alcohol → Ester + Water
Esters
Carboxylic Acid + Alcohol → Ester + Water
Smells eg. pear drops (nice)
Used in fragrances, food, solvents etc
Making: heat alcohol and carboxylic acid under reflux with concentrated sulfuric acid (catalyst)
Reflux: heating under reflux prevents products escaping as they condense and fall back
Distillation: esters generally have lower boiling points than reactants
Purification: impurities dissolve in aqueous solution and then is tapped off
Drying: anhydrous (without water) calcium cholride absorbs water in organic ester layer which is then filtered off
Distillation: to remove impurities
Fats and Oils
Fats and oils are naturally occuring esters
Glycerol + fatty acids --> fats (alcohol + carboxylic acid --> ester + water),
They are long molecules and used as an energy store
Animal fats: solid, saturated (single bonds)- cannot add other atoms, bad for the heart
Vegetable fats (oil): unsaturated (double bonds)- able to snap open and introduce new atoms, healthier
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