3.3.1- Introduction to organic chemistry/combustion/cracking/pollution Flashcards
What is nomenclature?
describing, classifying, and naming organic compounds
What is isomerism?
substances that have the same molecular formula but different structural formulas
What is an organic molecule?
contain carbon covalently bonded to at least one other element
What is a hydrocarbon?
compound containing only hydrogen and carbon atoms
What is a covalent bond?
a single shared pair of electrons
What bonds are polar?
C-N/C-O/C-Halogen
What bonds are non-polar?
C-C/C-H
Why is bond polarity important?
it is important in dictating the way organic molecules react chemically
What is polar bonding?
the bonding pair of electrons are unequally shared between the atoms
What is non-polar bonding?
the bonding pair of electrons are equally shared between the atoms
What is a saturated molecule?
contains only single c-c bonds
What is an unsaturated molecule?
contains at least one double or triple c-c bond
Why are they called unsaturated?
as the double bond can be broken to allow the addition of other groups/atoms
What is the name for chain molecules?
aliphatic
What is the name for ring molecules?
cyclic
What is special about aromatic molecules?
they contain at least one benzene ring
Name the 5 different ways of writing formulas
molecular/structural/skeletal/abbreviated structural/empirical
What is the molecular formula?
gives the actual number of atoms of each element present in the molecule
What is the structural formula?
shows all of the atoms present and how they are bonded together
What is the abbreviated structural formula?
used instead of the full displayed formula usually when writing balanced symbol equations as it is easier
What is the skeletal formula?
only shows the bonds of the carbon skeleton, and assumes that all the C-H bonds that can happen are there
What is the empirical formula?
the simplest whole number ratio of atoms of each element present in one molecule
What is the arrangement of the bonds around carbon in real life referred to as?
tetrahedral
What is the bond angle between C-C bonds?
109.5
What are the 5 steps to calculating the empirical formula?
1- list all the elements in a compound
2- underneath write out their % abundance or mass
3- divide each %/mass by the relative mass (Ar)
4- turn these answers into a simple ratio (divide all by the smallest number)
5- get the ratio in it’s simplest, whole number ratio, this is the empirical formula
How do you use the empirical formula to find the molecular formula?
divide the molecular mass by the empirical mass, then multiply the empirical formula by that answer, giving you the molecular formula
What is the relationship between molecular mass and empirical formula?
molecular formula is a multiple of the empirical formula
What is a functional group?
an atom or a group of atoms that determine the chemical properties of the molecule
What is similar about the organic molecules that have the same functional group?
they all react chemically in a similar way
What is a homologous series?
a family of molecules that can all be represented by the same general formula
What is special about the physical traits of homologous series’?
shows gradual trends in physical trends as the carbon chain gets longer
What is special about the physical traits of homologous series’?
shows gradual trends in physical trends as the carbon chain gets longer
What do the general structure not apply to?
cyclic structures
Explain Van der Waals forces
alkanes are non-polar, electrons in a molecule are constantly moving and at any one moment there could be an unequal distribution of the electron cloud, resulting in a temporary dipole, this can then induce a temporary dipole in a neighbouring molecule, then repeats over and over
Explain the trends in boiling points of homologous series’
b.p increases as number of carbons increases, as the alkanes have weak forces of attraction between neighbouring forces, and therefore all have relatively low b.p
-as size increases, the strength of the Van der Waals forces increases due to increased points of contact between neighbouring molecules, so the b.p increases due to more energy required to release the individual molecules as a gas
What is the general formula for alkanes?
CnH2n+2
What is the general formula for alkenes?
CnH2n
What is the general formula for haloalkanes?
CnH2n+1X
What is the general formula for alcohols?
CnH2n+2O
What is the general formula for carboxylic acids?
CnH2nO2
What is the general formula for aldehydes?
CnH2nO
What is the general formula for ketones?
CnH2nO
What is the functional group of alkanes?
C-H single bond
What is the functional group of alkenes?
C=C double bond
What is the functional group of haloalkanes?
-X
What is the functional group of alcohols?
-OH
What is the functional group of carboxylic acids?
C=O
[
OH
What is the functional group of aldehydes?
C=O (at the end of a molecule)
[
H
What is the functional group of ketones?
C=O (in the middle of a molecule)
[
What are the three types of structural isomer?
chain/positional/functional group
When do chain isomers occur?
when there are two or more ways of arranging the carbon skeleton of a molecule, can either be straight or branched
Why do branched isomers have a lower boiling point than straight chain isomers?
because branched chain isomers are spherical shaped and so have fewer points of contact between neighbouring molecules, which mean less points to induce temporary dipoles, so the Van der Waals forces are weaker
What is a position isomer?
same molecular structure, same carbon skeleton, same functional group, but the functional group is on different places in the carbon skeleton
What is a functional group isomer?
same molecular formula but different functional groups, so they belong to different homologous series
What is an example of functional group isomers?
propanal (aldehyde) and propanone (ketone) both have the same molecular formula (C3H6O)
What is the bond angle of C=C, and what is it called?
called planar, is 120
What are the three different types of halogenoalkane?
primary, secondary, tertiary
What is cracking?
the process by which large alkane molecules are broken down into smaller, more useful molecules
What is petroleum/crude oil?
a sticky, tarry substance that is a complex mixture of hydrocarbons (mainly straight-chain alkanes) that is finite and non-renewable
When was petroleum/crude oil formed and how?
from the dead remains of many tiny sea creatures called plankton that sank to the bottom of oceans, and were covered by many layers of sedimentary rock over 300 million years ago
How did the conditions lead to the organic material being converted into oil and gas?
more layers = higher temperature (generated by decomposition) and higher pressure (created by the weight of the overlying rock) in the absence of air forms oil and gas
What happens to the oil formed?
it is absorbed by porous rock, and is less dense than water so migrates upwards until it is trapped under impermeable rock, until it is drilled for and brought to the surface
What happens to the natural gas (CH4) formed?
it forms a pocket at the surface of oil reservoirs
Why does petroleum/crude oil need to be separated?
bad fuel, useless by itself
How is petroleum/crude oil separated?
fractional distillation
What are fractions?
a group of hydrocarbons that all have a boiling point within a set range
What type of a process is fractional distillation?
physical process
What are the steps of fractional distillation?
-crude oil is heated until it vaporises, then it is passed into a fractionating column/tower
-the column is then kept very hot at the bottom and cooler at the top, creating a negative temperature gradient
-the largest hydrocarbons remain at the bottom as liquids, called the residue, whereas the lighter hydrocarbons rise until they reach the level in the column where the temperature is equal to it’s boiling point, where it then condenses and is collected in trays
List the fractions from lowest b.p to the highest b.p
LPG/petrol/naphtha/kerosene/diesel/mineral oil/fuel oil/ wax, grease/bitumen
What are the properties of the fractions that condense at a lower temperature?
small molecules/ low b.p/ light in colour/ highly flammable/ low viscosity
What are the properties of the fractions that condense at a higher temperature?
long molecules/ high b.p/ dark in colour/ hard to light/ high viscosity
Why does fractional distillation work?
the different fractions that have different b.ps, and the short straight chain hydrocarbons have weak Van der Waals forces (less points of contact between neighbouring molecules) so have a lower b.p, opposite for the long straight chain hydrocarbons
What is LPG used for?
gas cookers/gas fires
What is petrol/gasoline used for?
petrol
What is naphtha used for?
petrochemicals
What is kerosine used for?
jet fuel
What is gas oil/diesel used for?
central heating fuel
What is mineral oil used for?
lubricating oil
What is fuel oil used for?
fuel for ships
What is wax/grease used for?
candles/polishing waxes
What is bitumen used for?
road surfacing
What is cracking?
the process by which large alkane molecules are broken down into a smaller, more useful molecules
What can the alkene products be used for?
making plastics (ethene-polyethene)
Why are the products of cracking sometimes different to what is predicted?
because it is a crude reaction- the long chain alkane can be broken up in a number of different ways
What are the two types of cracking?
thermal and catalytic
What are the conditions used in thermal cracking?
high temperature-up to 1000 degrees C, and high pressure- at around 70atm IN THE ABSENCE OF AIR
Why must thermal cracking be carried out in the absence of air?
otherwise alkane combustion occurs
Why is heat required in thermal cracking?
to provide the energy to break the strong C-C and C-H bonds
Which bonds are weaker and what does this mean?
C-C bonds are weaker than C-H bonds which means more C-C bonds are broken than C-H bonds
How is decomposition avoided during thermal cracking?
the time that the alkane is exposed to the high temperatures is very short
What is the exposure time called and how long is it for?
the residence time, approx. 1 second
Why is thermal cracking a high cost process?
due to the conditions required - high pressures require an expensive reaction vessel - high temperatures are more expensive to maintain
What is an advantage of thermal cracking?
it can be used on all long chain alkanes (including the residue)
What type of mechanism does thermal cracking occur by?
via a free-radical mechanism
What is homolytic fission?
the bond breaks evenly and each carbon atom from the C-C bond each receives one of the covalently shared electrons
What is a radical?
a species with an unpaired electron
How is thermal cracking started?
by the homolytic fission of a C-C bond to form two alkyl radicals
What is the difference in temperatures in catalytic cracking and thermal cracking and why?
catalytic cracking can be carried out at a much lower temperature due to a catalyst used
What is the catalyst used in catalytic cracking?
a zeolite catalyst (a crystalline aluminosilicate)
What is the advantage of the structure of this catalyst?
it provides a series of pores and interconnecting channels, which create a large surface area. the pore size can also be altered to accommodate the hydrocarbon molecules that are cracked inside the structure
What are the conditions of catalytic cracking?
slight pressure just above atmospheric pressure, and a temperature of around 450 degrees C, and the use of zeolite catalysts
What are the products of catalytic cracking?
mainly branched alkanes, cycloalkanes, and aromatic hydrocarbons
What is catalytic cracking mainly used for and why?
for producing motor fuels/petrol, because the proportion of alkenes produced is so small
Why are branched chain alkanes used in petrol?
prevents the preignition of gaseous vapours (aka ‘knocking’) due to the high pressure in a petrol engine, which helps the fuel burn more smoothly
What mechanism does catalytic cracking occur by?
via a mechanism that involves a carbocation intermediate
What is a carbocation and when is it produced?
a molecule containing a positively charged carbon atom (that can only form 3 covalent bonds) and it is produced during catalytic cracking
What else can zeolite be used for and why?
as a molecular sieve, due to its small pores that allow straight chain alkanes through but not branched chain molecules
What are the economic reasons for cracking alkanes?
heavy fractions are converted into higher value products, and alkenes that are produced can be used to make plastics
What is a fuel?
a substance that is burnt to release energy
What are exothermic reactions?
reactions that release heat energy to the surroundings
Is alkane combustion exothermic or endothermic?
very exothermic
Why is an initial supply of energy needed in catalytic cracking in order for the reaction to take place?
to overcome the activation energy (initial bond breaking process)
Why does the reaction continue after the initial energy?
because some of the energy released by the exothermic reaction is used to overcome the activation energy
What are the products of complete combustion?
carbon dioxide and water
What are the products of incomplete combustion?
carbon monoxide and water
Why is carbon monoxide toxic?
it combines with haemoglobin in the blood and reduces it’s oxygen carrying capability, potentially causing accidental death by suffocation
What is the problem of incomplete combustion of a petrol engine, and of a diesel engine?
it produces carbon monoxide - petrol
it produces carbon particulates (soot) - diesel
What is the problem of unburned hydrocarbons escaping in exhaust fumes?
they may contain benzene which is a known carcinogen, and can also react with sunlight and nitrogen to produce ground level o-zone (contributing to smog)
What is the problem of oxides of nitrogen (NOx) that are present in exhaust fumes?
they cause several pollution problems like acid rain
What is the problem of combustion?
produces CO2, which is a greenhouse gas that contributes to global warming
What does nitrogen dioxide react with to form photochemical smog?
with unburned hydrocarbons in the presence of sunlight
Why is the lead that is burnt when added to fuel a problem?
lead builds up in the body tissue and can damage the nervous system
What is the problem of sulphur impurities in hydrocarbon fuels?
when it is burned, sulphur can react with the oxygen in the air, which can result in the formation of sulphur dioxide, which causes air pollution and can cause acid rain
What is acid rain caused by?
the presence of non-metal oxides in the atmosphere
What is the product when sulphur di/trioxide is dissolved in water to form acids?
SO2 = H2SO3 (sulphurous acid)
SO3 = H2SO4 (sulphuric acid)
How can the sulphur impurities be removed from the flue gases?
by a process called flue-gas desulphurisation/ a reaction with an alkali
What is the alkali used to remove the sulphur dioxide?
calcium oxide (CaO)
How is calcium oxide obtained and what is the equation?
by heating calcium carbonate
CaCO3 —> CaO + CO2
Name the three greenhouse gases
carbon dioxide, water vapour, methane
How do greenhouse gases contribute to global warming?
they absorb infra-red radiation
How do the greenhouse gases absorb the infra-red radiation?
the bonds absorb it
What methods have the government introduced to control/deduce the CO2 emissions?
car manufactures must publish CO2 emissions data for their vehicles
other fuels/energy sources are being considered as alternatives to fossil fuel combustion
Explain the greenhouse effect
ultraviolet and visible radiation from the sun is absorbed by the Earth, this is emitted at much longer wavelengths (infra-red), some Infra-red radiation is absorbed by molecules in the atmosphere which trap the energy and prevent it’s escape, the gases that absorb this infra-red radiation are known as the greenhouse gases and the result is that the atmosphere warms up
What do catalytic converters do and where are they fitted?
they are fitted to the exhaust systems of modern cars to help remove carbon monoxide, nitrogen oxides, and unburned hydrocarbons
What do catalytic converters contain?
they contain a honeycomb of ceramic material that is thinly coated in d-block transition metal catalysts
Name 3 examples of metals that could be inside catalytic converters
platinum, palladium, rhodium
Why is the honeycomb structure beneficial?
it provides a large surface area which increases the efficiency of the catalyst and reduces the amount of catalyst needed and hence the cost
How does the catalytic converter work?
the metals inside the converter catalyse a series of reactions between the pollutants (reduction and oxidation reactions)
What percentage of pollutant gases are removed by these reactions inside a catalytic converter?
up to 90%
What happens when you use leaded petrol in a car fitted with a catalytic converter?
lead poisons the catalyst as pollutant gases usually weakly, temporarily bond to the catalyst surface for the reactions to occur, but this is prevented if lead coats the surface of it
Why does the sparking (2500 degrees C) of the combustion mixture lead to the formation of nitrogen monoxide and what else can this become?
the oxygen for petrol combustion comes from the air (20% oxygen, 80% nitrogen) which means that when the combustion mixture is sparked, the very high temperature can also overcome the activation energy required for the reaction between oxygen and nitrogen, forming nitrogen monoxide, which can then react with oxygen in the air to become nitrogen dioxide
What can nitrogen dioxide then do and why is this a problem?
react with rainwater and more oxygen to form nitric acid, a major component of acid rain
What is the product of adding calcium oxide to sulphur dioxide and what can it be used for?
CaSO3 - calcium sulphite and is easily oxidised to form calcium sulphate (gypsum) which is used in the building industry to make plasterboard
How else can SO2 be removed?
using a suspension of limestone in water
Summarise the acid rain process
acidic gases are released into the atmosphere, then are carried by the wind, then dissolve in rainwater to form acid rain which kills plant life, pollutes rivers and streams and erodes stonework
What is the functional group isomer of an alkene?
a cycloalkane
