Homologous series Flashcards
1
Q
What is a family of compounds known as?
A
a homologous series
2
Q
What are hydrocarbons?
A
compounds that contain hydrogen and carbon only
3
Q
What are the alkanes?
A
the alkanes are a homologous series of saturated hydrocarbons where all carbon to carbon bonds are single covalent bonds
4
Q
What is the first member of the alkane homologous series?
A
Methane
5
Q
What is the third member of the alkane homologous series?
A
Propane
5
Q
What is the second member of the alkane homologous series?
A
Ethane
6
Q
What is the fourth member of the alkane homologous series?
A
Butane
7
Q
What is the fifth member of the alkane homologous series?
A
Pentane
8
Q
What is the sixth member of the alkane homologous series?
A
Hexane
9
Q
What is the seventh member of the alkane homologous series?
A
Heptane
10
Q
What is the eight member of the alkane homologous series?
A
Octane
11
Q
What is the molecular formula for methane?
A
CH4
11
Q
What is the molecular formula for ethane?
A
C2H6
12
Q
What is the molecular formula for propane?
A
C3H8
13
Q
What is the molecular formula for butane?
A
C4H10
14
Q
What is the molecular formula for pentane?
A
C5H12
15
Q
What is the molecular formula for hexane?
A
C6H14
16
Q
What is the molecular formula for heptane?
A
C7H16
17
Q
What is the molecular formula for octane?
A
C8H16
18
Q
Physical state of methane at room temp?
A
gas
19
Q
Physical state of ethane at room temp?
A
gas
20
Q
Physical state of propane at room temp?
A
gas
21
Q
Physical state of butane at temp?
A
gas
22
Q
Physical state of pentane at temp?
A
liquid
23
Physical state of hexane at temp?
liquid
24
Physical state of heptane at temp?
liquid
25
Physical state of octane at temp?
liquid
26
Full structural formula for butane?
H H H H | | | | H—C—C—C—C—H | | | | H H H H
27
Shortened structural formula of butane
CH3CH2CH2CH3 OR CH3(CH2)2CH3
28
General formula for the alkanes
CnH2n+2
29
What are examples of physical properties?
-melting points -boiling points -viscosity -colour
30
Describe the physical properties of the alkanes
for the melting and boiling point data for alkanes, there is a gradual increase from methane to octane. longer chains have higher melting and boiling points as bigger molecules have stronger forces of attraction between them and so it takes more energy to separate the bigger alkane molecules from each other they are insoluble in water
31
What are the alkanes used for?
they are used as fuels
32
When alkanes burn completely what do they produce?
Carbon dioxide and water CH4 + O2 —-> CO2 + H20
33
What are the common features of the alkane homologous series?
same general formula similar properties- they all burn show a gradual change in physical properties - boiling points increase as the alkane molecules increase in size
34
What are known as isomers
compounds that have the same molecular formula but different structural formulae are known as isomers
35
What different things do isomers have?
Isomers have different physical properties
36
As the alkanes become larger in size what happens to isomers
the number of isomers fore each alkane increases too e.g. pentane has three isomers and hexane has five isomers
37
What are the rules for naming branched alkanes?
Identify the longest chain of carbon atoms and name the alkane with this number of carbon atoms identify the branch and name it according to the number of carbon atoms in the branch number the branch so that it has the lower of two possible numbers (what carbon atom it comes off)
38
When there is only one branch what is the name, the structure of the branch?
methyl -CH3
39
When there is only two branches what is the name, the structure and the prefix of the branch?
ethyl -C2H5 di
40
When there is only three branches what is the name, the structure and the prefix of the branch?
propyl -C3H7 tri
41
If there were two methyl branches what prefix would we add?
di
42
If there is only one way to draw a branch (such as methylbutane) what do we not need to do?
Use a number to indicate from which carbon atom it stems off
43
If there are two methyl branches on the third and fourth carbon atom how would we write the formula (for hexane)?
3,4 dimethylhexane
44
Definition of physical properties within homologous series’
something that can be observed or measured e.g. melting and boiling points, viscosity and colour
45
What are the cycloalkanes?
a homologous series of hydrocarbons where the carbon atoms join together to form a closed ring
46
Name the cycloalkanes
cyclopropane cyclobutane cyclopentane cyclohexane cyclohexane cyclooctane
47
What is the molecular formula of cyclopropane?
C3H6
48
What is the molecular formula of cyclobutane?
C4H8
49
What is the molecular formula of cyclopentane?
C5H10
50
What is the molecular formula of cyclohexane?
C6H12
51
What is the molecular formula of cycloheptane?
C7H14
52
What is the molecular formula of cyclooctane?
C8H16
53
What state at room temperature is cyclopropane?
gas
54
What state at room temperature is Cyclobutane?
gas
55
What state at room temperature is Cyclopentane?
liquid
56
What state at room temperature is Cyclohexane?
liquid
57
What state at room temperature is Cycloheptane?
liquid
58
What state at room temperature is Cycoloctane?
liquid
59
What is the general formula of the cycloalkanes
CnH2n
60
Describe the physical properties of the alkanes
Insoluble in water but soluble in nonpolar solvents like hexane or benzene.
Melting and boiling points increase with the number of carbon atoms due to stronger London dispersion forces.
Branching lowers the boiling and melting points compared to straight chains.
61
Describe the chemical properties of the cycloalkanes
Like other alkanes, cycloalkanes can be hydrogenated in the presence of a catalyst, though they are already saturated.Cycloalkanes are relatively stable due to their saturated structure (single bonds), making them less reactive than unsaturated hydrocarbons (like alkenes).
62
What are the uses of the cycloalkanes ?
They can be used as - solvents like industrial applications and the extractions of oils and fats.
Fuel like gasoline.
Lubricants and waxes.
63
What are the alkenes?
Methene, ethene, propene, butene, pentene, hexene, heptene, octene
64
What is the general formula for the alkenes ?
CnH2n
65
What does the fact that the cycloalkanes and the alkenes have the same general formula allow us to conclude?
Cycloalkanes have a ring structure with single bonds between carbon atoms and no double bonds.
Alkenes have a double bond between carbon atoms and an open-chain structure.
Although their formulas are the same, their structural arrangements differ, making cycloalkanes saturated and alkenes unsaturated.
66
What are the names of the alkenes?
Ethene, propene, butene, pentene, hexene, heptene, octene
67
What is the shortened structural formula of ethene?
CH₂=CH₂
68
What is the shortened structural formula of propene?
CH₂=CH-CH₃
69
What is the shortened structural formula of hexene?
CH₂=CH-CH₂-CH₂-CH₂-CH₃
70
How can we work out the molecular formula for the alkenes?
Start with the general formula: Alkenes follow the general formula CₙH₂ₙ (where n is the number of carbon atoms).
Count the carbon atoms: Determine the number of carbon atoms in the compound.
Calculate the hydrogen atoms: For every carbon atom, there will be two hydrogen atoms, minus any hydrogens involved in the double bond or substituents.
71
Ethene State at room temperature
gas
72
Propene state at room temperature
gas
73
butene state at room temperature?
liquid
74
pentene state at room temperature
liquid
75
hexene state at room temperature
liquid
76
heptene state at room temperature
liquid
77
octene state at room temperature
liquid
78
What temperature is room temperature ?
25C
79
How can alkenes also form isomers?
Structural isomers: Differ in the position of the double bond or branching of the carbon chain (e.g., but-1-ene vs. but-2-ene).
Geometric (cis-trans) isomers: Occur due to restricted rotation around the double bond, where groups attached to the double-bonded carbons differ in spatial arrangement (e.g., cis-but-2-ene vs. trans-but-2-ene).
80
how are the isomers of alkanes named?
Identifying the longest continuous carbon chain as the parent alkane.
Numbering the chain to give substituents the lowest possible numbers.
Naming and numbering the alkyl groups (substituents) attached to the chain.
Listing substituents alphabetically with their positions before the parent name.
Using prefixes like di-, tri-, etc., for multiple identical substituents.
81
How do we name an alkenes isomers
Identify the longest carbon chain containing the double bond.
Number the chain to give the double bond the lowest possible number.
Use the prefix for the number of carbons (e.g., eth-, prop-, but-).
Add the suffix -ene with the position of the double bond (e.g., but-1-ene).
82
How do we name an alkene’s iosmers when there are alos branches
where there are branches, the double bond takes priority over the branch
E.G
4-methlypent2ene
83
What is the general formula for the alkenes?
CnH2n
84
What does “saturated” mean?
a molecule contains only single bonds between carbon atoms, with each carbon fully bonded to the maximum number of hydrogen atoms. For example, alkanes are saturated hydrocarbons.
85
When there is multiple double bonds in an alkene what is used to indicated the number of double bonds
a prefix is used
Diene for two double bonds
Triene for three double bonds
86
Describe the physcial properties of the alkenes
Their melting and boiling points increase
They are insoluble in water
They burn to produce Co2 and H2O
Unsaturated
87
What does unsaturated mean in chemistry
a compound that can have more atoms added to it. It will contain at least one carbon-to-carbon double bond
88
What does the presence of the carbon-to-carbon double bond allow alkenes to take part in ?
an addition reaction
88
What is an addition reaction?
a chemical reaction where molecules add across a double bond
88
What do alkenes produce when they react with hydrogen gas
alkanes
89
What is the name of the reaction involving alkenes reacting with hydrogen gas to produce alkanes?
Hydrogenation
90
Define hydrogenation
an addition reaction where hydrogen is added across a double bond (alkene - alkane)
91
Following a hydrogenation reaction, is alkane said to be saturated or unsaturated - justify your answer
saturated because no more atoms can be added to the molecule
92
What is a convenient laboratory test for the presence of double bonds in a molecule
Ahake the compound with bromine solution
Alkenes cause the bromine solution to decolourise rapidly
With alkanes and cycloalkanes the bromine does not decolourise rapidly
The reaction with the alkene with bromine solution is an other example of an addition reaction: the bromine molecule adds across the double bond of the alkene
93
Describe alkenes reacting with the halogens
an addition reaction, forming dihalogenoalkanes. The reaction occurs via an electrophilic addition mechanism, where the π-bond of the alkene breaks, and halogen atoms bond to the carbon atoms.
94
What is formed when alkenes are made to react together?
Alkenes can be made to react with eachother to form very large compounds known as polymers
E.G.
ethene molecules can react with other ethene molecules to form polyethene
95
What are polymers
a very large molecule formed by the joining together of many smaller molecules (monomers)
96
What is hydration
a chemical reaction in which a molecule of water is added to an unsaturated hydrocarbon producing an alcohol
97
What is a homologous series
a group of molecules with the same general formula and similar chemical properties
98
What is fractional distillition
crude oil is a collection of hydrocarbons and during fractional distillation the crude oil is heated up and as each hydrocarbon has a different boiling point they can be collected individually
this results in long useless hydrocarbonic
99
Cracking hydrocarbons
cracking turns long saturated hydrocarbosn into two smaller hydrocarbons where one is saturated and the other is unsaturated
It is unsaturated as their is not enough hydrogens to make two alkanes
100
What do we use for petrols
short saturated molecules
101
What do we use for plastics
short unsaturated molecules
102
What do we need to remember in the experiment during crude oil
Before removing the heat from the delivery tube lift the delivery tube out of the bromine solution to prevent suck back
103
When one burns a hydrocarbon what is produces
CO2 which is linked to global warming and to climate change
