C10 - Organic Reactions Flashcards
What are alkenes
A homologous series of unsaturated hydrocarbons due to them having 2 less hydrogen atoms than the alkane with the same number of carbon atoms. This is becuase of the carbon carbon double bond in them
General formula for alkenes
CnH2n
First four alkenes
Ethene, Propene, Butene, Pentene
Methene doesn’t exist as methane only has 1 carbon atom
Defenition of a functional group
The part of a molecule that determins how it reacts e.g. the alkenes carbon-carbon double bond
Combustion of alkenes
- Produces unburnt carbon particles due to incomplete combustion
- This means they burn with a smoky flame
Reaction of alkenes with hydrogen and conditions required
- The two hydrogen atoms add ACROSS the double bond
- The carbon-carbon double bond is converted to a single bond
- So reacting an alkene with hydrogen produces an alkane
- The conditions required are nickel as a catalyst and 150°C
(Hydrogenation reaction)
Reaction of alkanes with water and conditions required
- The water must be steam
- The temperature and pressure must be relativley high
- Phosphoric acid is used as a catalyst
- This is a reversible reaction and it produces an alcohol e.g. ethanol
(Hydration reaction)
Reaction of alkenes with the halogens
- The two halogen atoms are added across the double bond
- The double bond is opened up into a single carbon-carbon bond
Uses of alcohols
- Fuels
- Alcoholic drinks
- Solvents
Functional group for alcohols
-OH (hydroxyl group)
first 4 alcohols and their structural formulas
Methanol - CH₃OH
Ethanol - CH₃CH₂OH
Propanol - CH₃CH₂CH₂OH
Butanol - CH₃CH₂CH₂CH₂OH
Two ways of making ethanol
- Reacting ethene with steam
- Fermentation of sugar cane
Conditions for fermentation
- Temperature is around 30°C
- Must have anaerobic conditions (no oxygen)
- Add yeast
- Slightly acidic conditions
Advantages and disadvantages of making ethanol by ethene and steam
- Fast and continuous process
- Produces pure ethanol
- However, crude oil is the source for lots of the ethene which is non-renewable
- Is an expensive process as energy is needed to increase the temperature and pressure
Advantages and disadvantages of making ethanol by fermentation
- Low temperature - the reaction doesn’t require lost of energy
- The sugar comes from plants so is renewable
- Is carbon neutral
- Produces an aqueous solution of ethanol (15%) so further fractional distillation needs to be done which is costly
- Ethical concerns about using food sources to make alcohol
- Is a batch process so is slow and laborious
Solubility of alcohols in water
The smaller chain alcohols up to and including propanol are all soluble in water and form neutral solutions
As the number of carbon atoms increases, the solubility decreases as the CH₃ part is hydrophobic
Equation for the reaction of sodium with ethanol
ethanol + sodium —> sodium ethoxide + hydrogen
Reaction of alcohols with an oxidising agent and give the name of it
- The oxidising agent used is acidified potassium dichromate
- The alcohol reacts to make a carboxylic acid and water
Combustion of alcohols
- They burn well with a clear flame
- This forms carbon dioxide and water
Functional group of carboxylic acids
COOH
What happens when carboxylic acids dissolve in water
- As they are weak acids, they ony partially ionise and this is shown by a reversbile reaction
- This gives a solution with an acidic pH
CH₃COOH ⇌ CH₃COO⁻ + H⁺
Reaction of a carboxylic acid witha metal carbonate e.g. ethanoic acid with sodium carbonate
ethanoic acid +sodium carbonate ⟶ sodium ehtanoate + carbon dioxide + water
What is an ester and what are they used for
pleasant smelling compunds that are used in artificial flavourings and perfumes (as they are very volatile)
reaction of ethanoic acid with ethanol
(carboxylic acid with an alcohol) and key points about the reaction
ethanoic acid + ethanol ⇌ ethyl ethanoate + water
* A sulfuric acid catalyst is needed
* The reaction is reversible
General formula for an Alcohol
CnH2n+1OH
