Section 3 - Pgs 45-48 Flashcards
What is a homologous series?
A group of compounds that can all be represented by the same general formula.
What colour flame does incomplete combustion of alkanes produce?
Smoky yellow
What are the first 4 alkenes called?
1) Ethene
2) Propene
3) Butene
4) Pentene
Compare the two methods of producing ethanol in terms of rate of reaction.
Ethene and steam: Very fast
Fermentation: Slow
What is the temperature, pressure and catalyst used for making ethanol from ethene and steam?
- 300*C
- 60-70 atm
- Phosphoric acid
What is a general formula?
An empirical formula that represents the composition of any member of an entire class of compounds.
Is there a molecule called “methene”?
No, there is not enough carbons to have a double bond. The first alkene is ethene.
What types of reactions do alkanes undergo?
- Combustion
- Substitution reactions
What is the process of turning ethanol into ethene called?
Dehydration -> Water needs to be removed
What colour flame does complete combustion of alkanes produce?
Blue
Compare the two methods of producing ethanol in terms of purity of the product.
Ethene and steam: Pure
Fermentation: Very impure -> Needs further processing
What is the general formula of alkanes?
CnH2n+2
How many carbon atoms are in ethane?
2
What is the general formula of alkenes?
CnH2n
What is the word equation for ethene reacting with bromine?
Ethene + Bromine -> Dibromoethane
What is organic chemistry?
Chemistry that deals with carbon compounds.
Write a symbol equation for the production of ethanol by fermentation.
C6H12O6 -> 2C2H5OH + 2CO2
Describe how ethene and steam can be used to produce ethanol.
- Ethene is taken from crude oil
- Ethene reacts with steam to produce ethanol
- Temperature of 300*C and 60-70 atm
- Phosphoric acid used as catalyst
Explain in detail the two ways in which a haloalkane can be formed.
Substitution in alkanes:
1) In the presence of UV light, a hydrogen atom in an alkane can be replaced by a bromine or chlorine atom.
2) The hydrogen that was replaced then reacts with the second halogen in its molecule, forming, for example, hydrogen bromide.
Addition in alkenes:
1) A C=C bond is split, allowing each of the two carbons to bind to a halogen atom.
2) There are no other products.
What is the general word equation for complete combustion of alkanes?
Alkane + Oxygen -> Carbon Dioxide + Water (+ Energy)
What are alkanes?
Alkanes are a homologous series of saturated hydrocarbons with the general formula: CnH2n+2.
What types of reactions do alkenes undergo?
- Combustion
- Addition reactions
What does saturated mean?
Containing only single bonds (so that no more molecules or atoms can join onto the molecule).
How can you test for the presence of carbon-carbon double bonds (i.e. whether a hydrocarbon is saturated or unsaturated)?
1) Shake the hydrocarbon with orange bromine water.
2) If the solution turns colourless, C=C bonds are present. If it doesn’t, then they are not.
How many carbon atoms are in propane?
3
How many carbon atoms are in pentane?
5
What is a substitution reaction?
When an atom is replaced by another. In alkanes, this is usually a hydrogen, which is replaced by a different atom (e.g. bromine)
Why does the bromine water test for carbon-carbon double bonds work?
1) The bromine is orange at first.
2) Adding an alkene causes the double bond to open up, adding the bromine to the molecule and making a dibromoalkane.
3) The dibromoalkane is colourless and there are no bromine molecules to give the solution an orange colour. This makes the solution colourless.
Give the symbol equation for turning ethanol into ethene.
C2H5OH -> C2H4 + H2O
Describe the process of turning ethanol into ethene.
Ethanol vapour is passed over a hot catalyst of aluminium oxide. (Diagram Pg 48 of revision guide)
What are alkenes?
Alkenes are a homologous series of unsaturated hydrocarbons with the general formula: CnH2n.
Compare the two methods of producing ethanol in terms of the availability of raw materials.
Ethene and steam: Ethene is from oil -> Finite resource
Fermentation: Sugar -> A renewable resource
How do alkanes react with halogens?
They can react with chlorine or bromine (halogens) to make haloalkanes in the presence of UV light. This is an example of a substitution reaction.
When do complete and incomplete combustion of alkanes happen?
- Complete combustion happens when there is sufficient oxygen
- Incomplete combustion happens when there is insufficient oxygen
What are hydrocarbons?
Molecules made up of hydrogen and carbon atoms only.
Give an example of a substitution reaction.
In the presence of UV light, methane reacts with bromine and a single bromine atom replaces a hydrogen atom in the methane molecule.
How many carbon atoms are in methane?
1
What is the general word equation for incomplete combustion of alkanes?
Alkane + Oxygen -> Carbon + Carbon Monoxide + Carbon Dioxide + Water (+ Energy)
Apart from ethanol, what else is produced during the fermentation of sugar?
Carbon dioxide
What is the word equation for methane reacting with bromine?
Methane + Bromine -> Bromomethane + Hydrogen bromide
How do alkenes react with halogens?
They make haloalkanes. This is an example of an addition reaction.
How many carbon atoms are in butane?
4
What are the products of complete and incomplete combustion of alkanes?
Complete: - Carbon Dioxide - Water Incomplete: - Carbon Dioxide - Water - Carbon - Carbon Monoxide
How many covalent bonds can a hydrogen atom make?
1
Compare the two methods of producing ethanol in terms of the continuity of the process.
Ethene and steam: Continuous
Fermentation: Batch
How do alkenes combust?
Just like alkanes do.
How many more atoms can join onto a double carbon in an alkene and why?
2 - The double bond opens up, meaning that the carbon either side of the bond can make an extra single bond with another atom.
Compare the two methods of producing ethanol in terms of cost.
Ethene and steam: High equipment cost + Low labour cost
Fermentation: Low equipment cost + High labour cost
What are isomers?
Molecules with the same molecular formula but different structures.
(e.g. Butene can have the double bond on a different pair of carbons in each isomer)
Describe how fermentation can be used to produce ethanol.
- Raw material is sugar
- Yeast is used to convert sugar into ethanol
- Temperature of 30*C
What is a symbol equation for the incomplete combustion of methane?
4CH4 + 6O2 -> C + 2CO + CO2 + 8H2O
(However, this is just an example. The products depend on the amount of oxygen. For example, there could be 7O2, but no carbon is produced.)
What does unsaturated mean?
Containing at least one double bond (so that they can make more bonds and other atoms or molecules can join onto the molecule).
What catalyst is used in turning ethanol into ethene?
Aluminium oxide
What are the advantages of complete combustion of alkanes over incomplete combustion?
- Releases more energy
- No poisonous gases
What is a good mnemonic for remembering the first 4 alkanes/alkenes?
Mice
Eat
Peanut
Butter
(Methane, Ethane, Propane, Butane)
What are the first 5 alkanes called?
1) Methane
2) Ethane
3) Propane
4) Butane
5) Pentane
What are haloalkanes?
Molecules which are formed when a halogen reacts with an alkane or alkene.
What are the two methods of producing ethanol?
- Fermentation
* Ethene and steam
Write a symbol equation for the production of ethanol from ethene and steam.
C2H4 + H2O -> C2H5OH
What is the symbol equation for the complete combustion of methane?
CH4 + 2O2 -> CO2 + 2H2O
How many covalent bonds can a carbon atom make?
4
