Organic chemistry Flashcards
1
Q
what is nomenclature?
A
describing, classifying,naming organic compounds
2
Q
Sumarise isomerism?
A
isomers are substances that have the same molecular formula but a different arrangement of atoms
3
Q
what are organic molecules
A
contain carbon and hydrogen e.g hydrocarbons
4
Q
what type of bonding occurs in organic molecules?
A
mainly covalent bonds
5
Q
what other atoms does carbon form covalent bonds with?
A
Carbon, hydrogen, nitrogen, oxygen, halogens
6
Q
if bonds are non-polar..?
if bonds are polar..?
A
- electrons are shared equally
- electrons are shared unequally
7
Q
are bonds between the C-C and the C-H polar or non-polar?
A
non-polar
8
Q
what type of bonding occurs between C-N, C-O, C-Halogen?
A
polar bonding
9
Q
what does bond polarity determined
A
the way organic molecules react
10
Q
why are alkanes saturated?
why are alkenes unsaturated?
A
- alkanes are molecules containing a single bond
- alkenes are molecules containing a double bond
11
Q
why are molecules said to be unsaturated?
A
because we can add more atomss/groups across the double bond
12
Q
carbon atoms that are arranged in chains are called
A
aliphatic molecules
13
Q
carbon atoms that are arranged in rings are called?
A
cyclical structures
14
Q
what is the molecular formula?
A
finds the actual number of atoms of each element present in the molecule
15
Q
what is the displayed/structural formula?
A
shows all the atoms and all the bonds present in the molecule
16
Q
what is the abbreviated structural formula?
A
used when balancing equations e.g CH3CH20H
17
Q
what is the skeletal formula?
A
only shows the bonds of the carbon skeleton
drawn as a zig zag
18
Q
What is the empirical formula?
A
the empirical formula of a compound is the simplest whole number ratio of atoms of each element present in the molecule
19
Q
Empirical Formula Calculations
A
20
Q
How do we calculate empirical formula calculations?
A
we can find the empirical formula of a compound from percentages or masses by using the following method:
- list all elements in the compound
- underneath, write their experimental percentage or mass
- divide each percentage or mass by the Ar for that particular element
- turn the numbers you get into simple ratios and into it’s simplest form
21
Q
form the empirical formula we can work out the..?
A
molecular formula
22
Q
question 1: A hydrocarbon W, contains 92.3% carbon by mass. the relative molecular mass of W is 78. Calculate the empirical and molecular formula of W.
A
empirical - 1:1 (CH)
molecular - C6H6
23
Q
Question 2: Compound A (Mr=58) has a percentage composition by mass of: C=62.04% H=10.41% O=27.55%
Calculate the molecular formula of A
A
empirical + molecular formula - C3H6O
24
Q
A chloroalkane, Z was shown to contain 37.2 carbon and 55% chlorine by mass. the remainder was Hydrogen. Calculate the empirical formula of compound Z
A
C2H5Cl
25
b) what additional information would be needed to calculate the molecular formula of compound Z?
would need the molecular mass
26
What is the functional group?
Is an atom or group of atoms that determine the chemical properties of the molecule
27
What part of the molecule is it?
The reactive part of the molecule
28
If an organic molecule has the same functional group they behave…?
Chemically in a similar way
29
What is the homologous series?
A name given to a family of molecules that can be represented by a general formula
30
All member of homologous series have the same functional group but..?
An increasing number of carbon atoms
31
Each successive molecule contains an additional…?
-Ch2- group
32
What do the homologous series show?
Gradual trend in physical in physical properties as carbon chain gets longer
33
Longer the hydrocarbon chain the..?
Higher the boiling point
34
What does the general formula not work for?
Cyclical structures
35
Why do aldehydes and ketones have the same general formula?
They are functional group isomers
36
Explain the structure of methane (3D and normal)
Bond angle?
Shape?
Arrangement of bonds is tetrahedral
Bond angle = 109.5
Atoms rotate freely
Occurs in all saturated molecule
37
Why do alkanes have a relatively low boiling point?
Have weak forces of attraction (weak van Der Waals forces between neighbouring molecules therefore have a low boiling point
38
Why does the boiling point increase as Alkane chain gets bigger?
As the size of alkane molecule increases the strength of Van Der Waals forces between the molecules increases (increased contact between neighbouring molecules so the bp increases so more energy must be supplied to release individual molecules as a gas
39
What is petroleum a mix of?
Separated by?
- mix of mainly alkanes
- separated by fractional distillation
40
What are structural isomers?
Compounds with the same molecular formula but different structural formula
41
3 different types of structural isomers
Chain isomers, positional isomers and functional group isomers
42
What is chain isomerism?
When there are 2 or more ways of arranging the carbon skeleton of a molecule (same molecular formula - different carbon skeleton)
43
The hydrocarbon chain can be either be…?
Branched or unbranched
44
Why do they share similar chemical properties?
They belong to the same homologous series
45
What differs?
Their physical properties
46
Why do branched-chain isomers have a lower bp?
Van Der Waals forces are weaker/ molecules are more spherical so fewer points of contact between neighbouring molecules
47
Chain isomers occur in all carbon compounds containing?
4+ carbon atoms
48
What is positional isomerism?
Have the same molecular formula the same carbon skeleton and same functional group but the functional group is joined at a different position on the carbon skeleton
49
Because of the different positions it can cause..?
Some differences in properties
50
What is functional group isomerism?
Have the same molecular formula but different functional group so belong to different homologous series
51
Since they have different functional groups they have?
Different chemical and physical properties
52
What kind of finite/non renewable resource is crude oil/petroleum
Fossil fuel
53
What is petroleum?
What is it a mixture of?
Type of Hydrocarbons?
A sticky and tary substance
Complex mixture of hydrocarbons (main straight chain alkanes)
Alkanes , cycloalkanes, aromatic hydrocarbons
54
How is crude oil/ petroleum formed?
- Formed from dead remains of vast numbers of tiny sea creatures and plants which sank to the bottom of the ocean and were covered by layers of sedimentary rock,
- as layers increased so did pressure and temperature
- under high pressure (created by weight of overlaying rock) and temperature (generated by decomposition) and absence of air/oxygen
55
What did this do?
What was oil absorbed by?
Why did the oil migrate upwards?
- Converted the organic material into oil and gas
- porous rock
- oil is less dense than water soo migrated upwards until trapped under impermeable rock
56
How do we extract crude oil?
How does natural gas stay under the surface?
- Drill into the ground ('traps') and pull it up to the surface
- forms a pocket at surface of oil reservoirs
57
How do we separate crude oil?
What type of process is fractional distillation?
- by fractional distillation
- physical process
58
Explain how different hydrocarbons are extracted from petroleum by fractional distillation?
- crusted oil is heated until vaporised
- the hydrocarbon vapour is then passed into a fractionating column
- the column is kept at a very high temperature at the bottom (350) and cooler toward the top
- the largest hydrocarbons remain liquids at temperatures as high as 350, they fall to the bottom of the column as residue
- the smaller hydrocarbons rise up the column in a gaseous state.
- as a particular hydrocarbon reaches the level in the column where temperature is equal to boiling point, it condenses and is collected
59
What type of hydrocarbons reach the top of the colum
Only the most volatile hydrocarbons reach the top of the column
60
How is the liquid collected?
What do the bubble caps do?
When vapour arrive at a tray that is sufficiently cool..?
- In a series of trays contains bubble caps
- force the rising vapours to pass through the liquid in the trays
- the vapours condense to a liquid then piped off separately
61
What is the fractionating responsible for ?
Explain why?
- primary distillation
- primary distillation does not separate individual hydrocarbons each fraction contains a mixture of hydrocarbons that have boiling points within a specific range
62
How can they be further separated?
- via secondary distillation to obtain purer products
63
After primary distillation the fractions are treated in several ways?
- some sulfur is removed to reduce the amount of pollution produced when the fractions used as fuels are burned in car engines
- some of the fraction is cracked to produce useful products
- residue is further distilled
64
What is vaccum distillation?
Allows the mixture to be separated at temperature below its normal boiling point - prevents components decomposing
65
Why do we use vaccum distillation?
At high temperature some components in residue decompose/ break down
66
Properties of short hydrocarbons
Properties of long hydrocarbons
- low bp, light in colour, highly flammable, low viscosity , more volatile
- high bp, dark in colour, low flammability, high viscosity, less volatile
67
Explain why shorter straight chain hydrocarbons have low boiling points?
Have weak Van Der Waals forces between neighbouring molecules so fewer points of contact so not much energy required to break forces so generally have low bp
68
Why do longer straight chain hydrocarbons have a higher boiling point?
Have stronger Van Der Waals forces between neighbouring molecules more points of contact so more energy required to break therefore has a boiling point
69
what are most fractions used for?
Why might some fractions be too valuable to burn?
- fuels.
- But petroleum is a finite resource, so when supplies become more limited may become to valuable to burn
70
which two substances are more likely to be cracked?
Naphtha and kerosine
71
what are the uses of Alkenes and Aromatics?
are useful starting materials (feedstock) for the petrochemical industry
72
what can they be converted into..?
important products such as plastics, dyes, detergents, medicines, paints and insecticides
73
Describe the boiling point, uses and approximate number of carbon atoms of liquified petroleum gas?
Bp - up to 25
Uses - gas cookers, gas fires, camping gas
n - 1-4
74
Describe the boiling point, uses and approximate number of carbon atoms in Petrol
Bp - 40-100
uses - petrol
n - 4-12
75
Describe the boiling point, uses and approximate number of carbon atoms in naphtha?
bp - 100-150
uses - petrochemicals
n - 7-14
76
Describe the boiling point, uses and approximate number of carbon atoms in kerosine (paraffin)
bp - 150-250
uses - jet fuel, petrochemicals
n - 11-15
77
Describe the boiling point, uses and approximate number of carbon atoms in gas oil (diesel)
bp - 220-350
uses - transport fuel, central heating fuel, petrochemicals
n - 15-19
78
Describe the boiling point, uses and approximate number of carbon atoms in mineral/lubricating oil?
bp - <350
uses - lubricating oil and petrochemicals
n - 20-30
79
Describe the boiling point, uses and approximate number of carbon atoms in fuel oil?
Bp - over 400
Uses - fuel for ships and power stations
n - 30-40
80
Describe the boiling point, uses and approximate number of carbon atoms in wax, grease
bp - over 400
uses - candles, grease for bearings, polishing waxes
n - 40-50
81
Describe the boiling point, uses and approximate number of carbon atoms in Bitumen (tar)?
Bp - over 400
uses - roofing, road surfacing
n - above 50
82
what is cracking?
large alkane molecules are broken down into more shorter more useful molecules
83
why are shorter molecules more in demand?
more useful, used in petrol
84
cracking breaks down...?
c-c bonds and (c-h)
85
write an equation for cracking?
large alkane ---> smaller alkanes + alkenes +(hydrogen)
86
why may we need to separate mixtures by fractional distillation (after cracking)?
when cracked molecules can break up in a number of different ways to form a mixture of hydrocarbons
87
these products will always contain less...?
carbon atoms than the original
88
what are the reaction conditions required for thermal cracking
- High temperature (400-900 C) and
- (High pressure) 7000kpa or 70atm
- In the absence of Oxygen
89
what is thermal cracking?
Thermal cracking takes place at high pressure and high temperature and produces shorter alkanes and a high percentage of alkenes
90
why do we have to do thermal cracking in the absence of air?
otherwise alkane combustion will occur
91
why are more c-c bonds broken ?
but at very high temperatures..?
c-c bonds are weaker (lower bond energy) than c-h bonds so more c-c bonds = broken
- c-h bonds break and hydrogen is formed
92
why is there a high proportion of shorter chain alkanes?
as temperature increases the carbon chain breaks nearer towards the end of the chain
93
how do we avoid the decomposition of alkanes?
limit the time they are exposed to high temperatures
94
what is the exposure time a.k.a and what is it?
residue time and approximately 1second
95
why is thermal cracking expensive?
requires high temperature and pressure so requires an expensive reaction vessel
96
thermal cracking occurs via a..?
a free-radical mechanism
97
what is a radical?
is a species with an unpaired electron
98
thermal cracking is started by..?
to form..?
- the homolytic fission of a c-c bond
- 2 alkyl radicals
99
what happens in homolytic fission?
in homolytic fission the bond breaks equally and each carbon atom from the c-c bond gets one of the covalently shared electrons
100
what is octane used in?
what is ethane used in?
- petrol
- to make plastics and antifreeze
101
what is catalytic cracking?
mainly used to produce..?
takes place at slight pressure, high temperature and in the presence of a zeolite catalyst, mainly used to produce motor fuels and aromatic hydrocarbons
102
how does a catalyst work?
reduces the activation energy required for te reaction so less energy is required
103
what happens in the catalytic cracker?
- hydrocarbons are vapourised
- mixed with a zeolite catatlyst
104
zeolites are synthetic which means..?
they're also ...?
they're man-made
modern catalysts
105
what is meant by catalysts are crystalline alluminosilicates?
they contain atoms of silicon, oxygen and aluminium
106
structure of a zeolite
why can the pore size be altered?
- series of pores and interconnecting chanels which create a large SA
- to accommodate hydrocarbon molecules which are cracked inside the structure
107
large alkanes are cracked to produce...?
mainly branched alkanes, cycloalkanes and aromatic hydrocarbons
108
since the proportion of alkenes produced is small this type of cracking is primarily used for...?
producing motor fuels and a major method for producing petrol
109
what are important components in petrol?
small branched chain alkanes and aromatic hydrocarbons
110
branched chain alkanes help...?
the fuel to burn more smoothly and therefore prevent petrol engine auto-ignition (knocking)
111
how can high pressure cause 'knocking'?
may cause the fuel air to mix to ignite before the spark is produced
112
in the past how was 'knocking' reduced explain why this is bad?
knocking was reduced in the past by adding lead components but now we know that lead can case pollution
113
catalytic cracking occurs via..?
a mechanism that involves carbocation intermediate
114
what is carbocation?
a molecule containing a positively charged carbon atom
115
how many covalent bonds does a positive carbon make?
3 covalent bonds
116
how does a zeolite function as a molecular sieve?
zeolites pores are small enough to allow straight chain alkanes to pass but branched chain molecules can not pass through as they are too bulky
117
zeolite is used to separate?
unbranched hydrocarbons that are used to make biodegradeable detergents
118
what is a fuel?
a substance that is burnt to release energy
119
what type of reaction is combustion?
exothermic
120
what happens in alkane combustion
alkanes heated in air to overcome the activation energy
121
combustion of octane equation?
C8H18 + 12.5o2 ----> 8co2 + 9h2o
122
why does this reaction have a high activation energy?
strong c-c and c-h bonds must be broken
123
where is the energy to overcome the activation energy supplied?
from a spark in the internal combustion engine
124
explain why the reaction is highly exothermic?
the energy released in the bond making is more than enough to compensate for the activation energy
125
what is complete combustion?
occus in a plentiful supply of oxygen
126
what is the equation for complete combustion?
ch4 + 2o2 ---> co2 + 2h20
127
as the number of carbon atoms increases..?
more oxygen is needed per alkane molecule and the reactions are more exothermic
128
how does incomplete combustion occur?
in an insufficent supply of oxygen the products are carbon monoxide and water but in some cases c-soot is formed
129
what are the two equations for incomplete combustion?
CH4 + o2 ----> c + 2H20
C4H10 +4.5O2 ---> 4CO + 5H20
130
`how is carbon monoxide released into the atmosphere?
from exhausts of petrol engine vehicles and badly maintained central heatings boilers and gas fires
131
explain the danger of carbon monoxide
carbon mooxide is a toxic gas which combines with haemoglobin in the blood and reduces the oxygen carrying cpacity leading to death by suffoctaion.
132
how is soot formed?
by incomplete combustion of diesel
133
unburned hydrocarbons escape in?
exhaust fumes
134
why are they known as a carcinogen?
they may contain benzene a known carcinogen
135
why are lead componds added to petrol?
to improve engine performance
136
explain why lead is dangerous?
lead build up in body tissue and can dammage the nervous system
137
how is the problem reduced?
by using unleaded petrol
138
how is carbon dioxide formed?
why is it bad?
- by complete combustion
- co2 is a greenhouse gas which contributes to global warming
139
explain how photochemical smog is formed?
nitrogen dioxide is present in exhaust gases which can react with unburned hydrocarbons in the presence of sunlight. The smog is produced via complex series of reactions involving free radicals
140
explain the harms smog causes?
contains chemical irritants (may increase summer increase in asthma attacks
141
how is acid rain formed?
by the presence of non-metal oxides in the atmosphere. mainly oxides of nitrogen and sulphur.
When the fraction e.g petrol is burned sulphur reacts with oxygen in the atmosphere to make oxides. Sulphur dioxide causes air pollution. These toxic oxides mix with rain water to make acid rain
142
what is sulphur?
an impurity in petroleum fractions
143
what is petroleum and sulphur made up of?
petroleum- remains of living organisms
sulphur - is a constituent of a protein
144
how is sulphur dioxide formed?
burning of fossil fuels
145
what are the two equations for sulphur dioxide?
S + O2 ----> SO2
CH3SH +3O2 -----> CO2 +2H2O +SO2
146
sulphur dioxide causes...?
Air pollution
147
sulphur dioxide can be further oxidised to?
sulphur trioxide
148
1. equation for sulphur trioxide
2. these both (sulphur dioxide + trioxide) are acidic oxides which dissolve to form?
- 2SO2 +02 ---->2SO3
2. SO2 + H20 ---> H2SO3 (sulphorous acid)
SO3 +H2O ----> H2SO4 (sulphuric acid )
149
what cause the most pollution/carbon emissions?
coal burning in power stations
150
how is sulphur dioxide produced?
burning of fuels in power stations
151
How is sulphur dioxide removed from flue/chimney gases?
how does this work?
- flue-gas desulphurisation
removed by reacting with an alkali - neutralisation reaction
152
which compound can be used to remove sulphur dioxide?
calcium oxide
153
how is calcium oxide obtained?
by heating calcium carbonate via thermal decomposition
154
equation for obtaining calcium oxide?
CACO3 -----> CAO + CO2
155
why is this a problem?
CO2 gas is produced - greenhouse gas
156
calcium oxide removes sulphur dioxide via (equation)
what type of reaction is this?
what does it form?
- CAO +SO2 -----> CASO3
- NEUTRALISATION REACTION
- FORMS CALCIUM SULPHITE
157
calcium sulphite is easily...?
what is gypsum used for?
- oxidised to form hydrated calcium sulphate (gypsum) CaSO4.2h2O
- in the building industry to make plasterboard
158
how else can SO2 be removed?
equation?
by using a suspension of limestone (calcium carbonate in water)
CACO3 + SO2 ------> CASO3 + CO2
159
where does nitrogen oxide come from?
what type of reaction is this?
the atmosphere is mainly composd of nitrogen =80% , oxygen = 20% combustion
160
how are oxides of nitrogen formed?
at very high temperatures which are high enough to overcome the activation energy for reaction between oxygen and nitrigen to form nitrogen dioxide
161
nitrogen of monoxide equation?
N2 + O2 -----> 2NO
162
nitrogen dioxide equation?
2NO +O2 -----> 2NO2
163
nitrogen dioxide reacts with rainwater + oxygen to form ...?
equation?
NITRIC ACID ( a major component in acid rain)
4NO2 + O2 + 2H2O-------> 4HNO3
164
What are catalytic converters?
Are fitted to exhaust systems of modern cars to remove carbon monoxide nitrogen oxides and unburned hydrocarbons.
165
Converters are usually a mixture of?
What Structure provides a…?
- platinum, palladium, rhodium
- honeycomb ( of ceramic material) structure provides a large SA this increases the efficiency of the catalyst and reduces the amount of catalyst needed hence the cost
166
The catalytic converters remove up to… of pollutant gases
90%
167
Example of converter reactions
1. 2CO + 2NO —> 2CO2 + N2
2. C8H18 + 25NO —-> 12.5N2 + 9H2O
168
In the catalytic converters:
Carbon monoxide is converted into..?
Oxides of nitrogen is converted to..?
Unburnt hydrocarbons converted to..?
- carbon dioxide
- nitrogen
- carbon dioxide and water
169
Explain why this is good?
Nitrogen is harmless
Co2 is less dangerous than CO
170
Why do converters only work with unleaded petrol?
Lead poisons the catalyst
171
FINISH
