7.2 Reactions of alkenes and alcohols (Triple) Flashcards
Triple Science only
What bond do alkenes have?
At least one double covalent bond
What is the general formula of alkenes
CnH2n
What are alkenes?
An unsaturated hydrocarbon with the functional group C=C.
What are the first four alkenes?
- Ethene (C2H4)
- Propene (C3H6)
- Butene (C4H8)
- Pentene (C5H10)
Why are alkenes described as unsaturated?
Alkenes contain two fewer hydrogen atoms than the alkane with the same amount of carbons.
What happens to molecules with the same functional group?
They react in similar ways
What are the addition reactions with alkenes? (4)
- (Incomplete) combustion (w/ oxygen)
- Hydrogenation (w/ hydrogen)
- Hydration (w/ water)
- Reaction with halogens
What do alkenes produce when reacting with oxygen in combustion? (3) Why?
- Water and carbon dioxide (like other hydrocarbons)
- Burn with a smokey flame; because they produce burnt carbon particles due to incomplete combustion.
What conditions are needed to react alkenes with hydrogen in hydrogenation? (2)
- Nickel catalyst
- ~150ºC
What do alkenes produce when reacting with hydrogen in hydrogenation? Why?
Alkanes; because the addition of hydrogen atoms across the carbon-carbon double bond causes the double bond to convert into a carbon-carbon single bond.
How do alkenes react with hydrogen, water and halogens?
By the addition of hydrogen atoms which causes the carbon-carbon double bond to convert into a carbon-carbon single bond.
What conditions are needed to react alkenes (ethene) with water in hydration? (4)
- Steam
- ~300ºC
- 70 atm
- Catalyst (e.g. phosphoric acid)
What type of reaction is the hydration reaction of alkenes and water?
Reversible
What is an advantage of making ethanol by hydrating ethene?
Produces a high yield of ethanol: can be increased by passing back any unreacted ethene and steam through the catalyst.
What do the first four alkenes produce when reacting with chlorine? (4)
- Dichloroethane
- Dichloropropane
- Dichlorobutane
- Dichloropentane
What do the first four alkenes produce when reacting with bromine? (4)
- Dibromoethane
- Dibromopropane
- Dibromobutane
- Dibromopentane
What do the first four alkenes produce when reacting with iodine? (4)
- Diiodoethane
- Diiodopropane
- Diiodobutane
- Diiodopentane
What are the main uses of alcohol? (3)
- Fuels
- Solvents
- Alcoholic drinks
What is the functional group for alcohols?
-OH
What are the first four alcohols?
- Methanol (CH3OH)
- Ethanol (C2H5OH)
- Propanol (C3H7OH)
- Butanol (C4H9OH)
What are the disadvantages of making ethanol by hydrating ethene?
- The reaction requires a lot of energy due to high temperatures
- The ethene comes from crude oil and is non-renewable.
What are ways to make ethanol? (2)
- Hydration of ethene
- Fermentation of sugar
Describe the process of fermentation to produce ethanol. (2)
1) Sugar solution (e.g. glucose) mixed with yeast.
2) Yeast converts sugar solution into solution of ethanol and produces carbon dioxide.
What conditions are needed to ferment sugar (e.g. glucose) to produce ethanol? (2)
- ~30ºC
- Anaerobic conditions
What are the advantages of producing ethanol using fermentation?
- Low temperature means lower amount of energy required.
- Sugar used from plants so is renewable.
What is the disadvantage of producing ethanol using fermentation?
Energy needed to purify ethanol by distillation as it is an aqueous solution.
What occurs when alcohol is added to water?
Alcohols are soluble in water and produce a neutral solution.
Describe the trends in solubility of alcohols in water.
As the number of carbon atoms increases, the solubility decreases.
What occurs when alcohol is reacts with sodium? (2)
- Effervescence
- Produces hydrogen and:
(a) sodium methoxide
(b) sodium ethoxide
(c) sodium propoxide
(d) sodium butoxide
What occurs when alcohol is reacts with oxidising agents? (1)
Produce carboxylic acid (e.g. methanol acid) and water.
What occurs when alcohol is reacts with oxygen (combusted)? (1)
Produces carbon dioxide and water
What are the first four carboxylic acids?
- Methanoic acid (HCOOH)
- Ethanoic acid (CH3COOH)
- Propananoic acid (C2H5COOH)
- Butananoic acid (C3H7COOH)
What occurs when carboxylic acid is dissolved in water? (2)
- They become weak acids
- They ionise to produce an ester and H+
Explain why carboxylic acids are weak acids in terms of ionisation and pH?
Carboxylic acids are considered weak acids as:
- They only partially ionise [they contain less hydrogen ions than strong solution of the same concentration]
- They have a higher pH than a strong acid of the same concentration.
What occurs when carboxylic acid is reacts with metal carbonate? (1)
- Produce and ester (e.g. ethyl ethanoate), carbon dioxide and water
What occurs when carboxylic acid is reacts with an alcohol? (1)
- Produce ester (e.g. ethyl ethanoate) and water
Why are esters useful?
- They often have a pleasant smell so are used in foods.
What conditions are needed to react carboxylic acids with alcohol? (2)
- Catalyst (e.g. sulphuric acid)
