Alkenes and alcohols
- Chemistry
- Properties of hydrocarbonsFunctional groups: Alkanes, alcohols, carboxylic acids and estersPolymers
- GCSE
- AQA
- Created by: Andrew
- Created on: 26-10-18 16:32
Alkenes
Definition: Unsaturated hydrocarbons with a C=C (carbon double bond) functional group
- Unsaturated - Not combined with as much hydrogen as possible
- Hydrocarbons - Molecules made from only carbon and hydrogen atoms
- Functional group - A group of atoms in a compound that determine the nature of the reaction that the compound will undergo
Properties:
- Highly reactive (due to carbon double bond)
- Homologous series (all have twice as many hydrogen atoms as carbon atoms)
- Unsaturated
The four shortest alkenes in order are: Ethene, propene, butene, pentene
Methene is not possible as it would have a single carbon atom so cannot have a C=C bond
Reactions of alkenes
Key points:
- The functional group (C=C double bond in alkenes) determines how it will react
- A common reaction for alkenes is addition reactions, the C=C bond opens and new atoms bond with the carbon
Some addition reactions with alkenes are:
- Alkene + water (steam) + posphoric acid catalyst --> alcohol
- Alkene + oxygen --> carbon monoxide + carbon (soot) + water (combustion)
- Alkene + hydrogen + nickel catalyst --> alkane (this process is called hydrogenation)
- Alkene + bromine water --> dibromoalkane (this can be used to differenciate between alkanes and alkenes as alkanes do not react with bromine water)
Image for addition reaction of an alkene
Alcohols
Definition: An organic compound with a hydroxyl (OH) functional group bonded to a saturated carbon atom
- Hydroxyl - An OH functional group
- Saturated - Bound to as much hydrogen as possible, no double (or more) bonds
The general formula for an alcohol is: CnH2n+1OH
The four smallest alcohols are: Methanol, ethanol (the alcohol we consume), propanol, butanol
Reactions of alcohols
- The funtional group for alcohols is a hydroxyl (OH) group
Some reactions of alcohols:
- Alcohol + water --> neutral solution
- Alcohol + air (and heat) --> carbon dioxide + water (combustion)
- Alcohol + oxidising agent --> carboxylic acid
- Alcohol + sodium --> hydrogen
Fermentation
A common method for producing ethanol, yeast is added to a sugar solution to produce ethanol and carbon dioxide.
Ideal conditions:
- 37°C
- Slightly acidic
- Anaerobic
Side note: This is how alcoholic drinks are made, the carbon dioxide produced is also what makes bread rise.
Carboxylic acids
Definition: An organic compound with a carboxyl functional group
- Carboxyl functional group - carbon with a double bond to oxygen and a single bond to a hydroxyl group, written as COOH
- The general formula for a carboxylic acid: CnH2n+1COOH
The four smallest carboxylic acids in order are: methanoic acid, ethanoic acid, propanoic acid, butanoic acid
Reactions of carboxylic acids
- The functional group is a carboxyl (COOH) group
Some reactions are:
- Carboxylic acid + a carbonate --> a salt + carbon dioxide + water
- Carboxylic acid + water + acid catalyst --> ester + water
- Carboxylic acid + water --> acidic solution
Addition polymerisation
Definition: The joining of short chain monomers (molecules in a polymer) to produce a long chain polymer
Important: Alkenes are used as monomers in addition polymerisation because their carbon double bonds open to bond to other monomers
- In this reaction, the polymer is the only product.
- Naming polymers is easy, just add "poly" in front of the monomers name
Example:
- Ethene monomers join to create poly(ethene)
- Propene monomers join to create poly(propene)
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