What is an alkane?
A saturated hydrocarbon. A compound of hydrogen and carbon only, with no C=C bonds.
What is the homologous series?
A 'family' of organic compounds that have the same functional group and similar chemical properties.
What do the alkanes form?
A homologous series
What do all homologous series' have/do?
- the same general formula
- differ by CH2 in molecular formulae from neighbouring members of the series
- show a gradual variation in physical properties, such as their boiling points
- similar chemical properties
What is the general formula for alkanes?
CnH2n+2 (where n is the number of carbon atoms in the molecule)
Decane is an alkane. Its molecules contain 10 carbon atoms. Predict the molecular formula of decane and explain your answer.
The formula will be C10H22. This is because n = 10. So, 2n+2 = (2 � 10) + 2 = 20 + 2 = 22.
Hexane is an alkane. Its molecules contain six carbon atoms. Predict the molecular formula of hexane.
The formula will be C6H14.
CH4
Methane
C2H6
Ethane
C3H8
Propane
C4H10
Butane
C5H12
Pentane
C6H14
Hexane
C7H16
Heptane
C8H18
Octane
C9H20
Nonane
C10H22
Decane
What does saturated mean?
Containing no carbon-to-carbon double bonds, only single bonds.
What is the general formula for alkenes?
CnH2n (where n is the number of carbon atoms in the molecule).
Decene is an alkene. Its molecules contain ten carbon atoms. Predict the molecular formula of decene and explain your answer.
The formula will be C10H20. This is because n = 10. So, 2n = (2 � 10) = 20.
Hexene is an alkene. Its molecules contain six carbon atoms. Predict the molecular formula of hexene.
The formula will be C6H12.
C2H4
Ethene
C3H6
Propene
C4H8
Butene
C5H10
Pentene
C6H12
Hexene
C7H14
Heptene
C8H16
Octene
C9H18
Nonene
C10H20
Decene
What are isomers?
Chemicals that have the same molecular formula but different arrangements of atoms.
Explain the relationship between but-1-ene and but-2-ene.
But-1-ene and but-2-ene have the same molecular formula, but the position of their C=C bond is different. The number in their names show where that bond is located in the molecule. But-1-ene and but-2-ene are isomers.
What is an alkene?
An unsaturated hydrocarbon
What is a hydrocarbon?
A compound that contains hydrogen and carbon only.
What does unsaturated mean?
Unsaturated means a compound contains at least one double or triple bond.
What is a functional group?
An atom, or group of atoms, that determines the main chemical properties of an organic compound.
What is the functional group in alkenes?
The C=C bond
What is the C=C bond responsible for?
The typical reactions in alkenes
What reaction do alkanes and alkenes both undergo?
Complete combustion
What is complete combustion?
Burning in a plentiful supply of oxygen or air. Complete combustion of a hydrocarbon produces water vapour and carbon dioxide.
What reactions do only alkenes undergo?
Addition reactions
What is an addition reaction?
A type of reaction in which two substances react together to form one new substance.
What does the complete combustion of alkanes and alkenes involve?
The oxidation of hydrocarbons
What is oxidation?
The gain of oxygen, or loss of electrons, by a substance during a chemical reaction.
What does the complete combustion and oxidation of alkanes and alkenes produce?
Carbon dioxide and water
Change this word equation into a symbol equation: Ethane + oxygen ? carbon dioxide + water
C2H6(g) + 3�O2(g) ? 2CO2(g) + 3H2O(l)
Change this word equation into a symbol equation: Ethene + oxygen ? carbon dioxide + water
C2H4(g) + 3O2(g) ? 2CO2(g) + 2H2O(l)
Why are more molecules of oxygen needed to balance the equation for ethane?
Because the alkane contains more hydrogen atoms which need to be oxidised to form water molecules.
Describe how alkanes and alkenes are oxidised during complete combustion. This creates the products carbon dioxide and water.
The alkanes and alkenes react with oxygen. Their carbon atoms and hydrogen atoms gain oxygen.
How are alkenes allowed to undergo addition reactions?
Because of the functional group, C=C
Ethene reacts with bromine to make...?
dibromoethane:
What is the balanced equation for ethene + bromine ? dibromoethane
CH2=CH2 + Br2 ? CH2BrCH2Br
What is a covalent bond?
A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons.
Why is CH2=CH2 + Br2 ? CH2BrCH2Br an addition reaction?
Because one molecule combines with another molecule, forming one larger molecule and no other products.
Propene, CH3CH=CH2, reacts with bromine. Predict the structure of the product formed.
CH3CHBrCH2Br
But-1-ene, CH2=CHCH2CH3, reacts with bromine. Predict the structure of the product formed.
The structure is: CH2BrCHBrCH2CH3
How can you distinguish between alkanes and alkenes?
An orange-brown solution of bromine dissolved in water, called bromine water, is used to distinguish between alkanes and alkenes
What happens to bromine water when mixed with an alkane?
There is no change when bromine water is mixed with an alkane
What happens to bromine water when mixed with an alkene?
The bromine water becomes colourless when it is mixed with an alkene
Colour of small alkanes?
Light
Colour of large alkanes?
Dark
Viscosity (gloopiness) of small alkanes?
Low
Viscosity (gloopiness) of large alkanes?
High
Boiling point of small alkanes?
Low
Boiling point of large alkanes?
High
How volatile are small alkanes? (how easily do they turn into gases?)
Volatile (turn into gases easily)
How volatile are large alkanes? (how easily do they turn into gases?)
Not volatile (do not turn into gases easily)
Flammability of small alkanes?
High
Flammability of large alkanes?
Low
How useful are small alkanes as fuels?
Useful
How useful are large alkanes as fuels?
Useless
Boiling point of methane?
-162
Boiling point of ethane?
-89
Boiling point of propane?
-42
Boiling point of butane?
-1
Boiling point of pentane?
36
Boiling point of hexane?
69
Boiling point of heptane?
98
Boiling point of octane?
126
Boiling point of nonane?
151
Boiling point of decane?
174