module 4 Flashcards
hydrocarbon definition
compound consisting of hydrogen and carbon ONLY
saturated definition
contains single carbon-carbon bonds only
unsaturated definition
contains a c-c double bond
molecular formula
formula showing the actual number of each type of atom
empirical formula
shows the simplest whole number ratio of atoms of each element in the compound
general formula
the simplest algebraic
formula of a member of a homologous series
structural formula
the minimal detail that shows the arrangement of atoms in a
molecule
displayed formula
shows all the covalent bonds present in a molecule
skeletal formula definition
the simplified organic
formula, shown by removing hydrogen atoms from alkyl chains, leaving just a
carbon skeleton and associated functional groups
aliphatic
alicyclic
aromatic
- definitions
- a compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings
- an aliphatic compound arranged in non-aromatic rings with or without side chains
3.a compound containing a benzene ring
homologous series
families of organic compounds with the same functional
group and same general formula.
- They show a gradual change in physical properties (e.g. boiling point).
- Each member differs by CH2
from the last.
- same chemical properties.
functional group
an atom or group of atoms which when present in different molecules
causes them to have similar chemical properties
structural isomer
same molecular formula but different structural formulae
homolytic fission
heterolytic fission
- definitions
- each bonding
atom receives one electron from the bonded pair, forming two radicals - one bonding
atom receives both electrons from the bonded pair
free radical definition
a reactive species which possesses an unpaired electron
what does a curly arrow show
movement of a pair of electrons
alkanes
- formula
- saturated or unsaturated
- shape around carbon atom
- bond angle
- CnH2n+2
- saturated
- tetrahedral as four bonded pairs of electrons repel equally
- 109.5
how does the sigma bond form in alkanes
- one sp3 orbital from each carbon overlap to form a single C-C bond called a sigma bond
- rotation around this bond can occur
why does boiling point increase as alkanes get bigger
- increased number of electrons
- increases size of the induced dipole-dipole interactions between molecules
- long chain alkanes have a larger surface area of contact between molecules for London forces to form, this leads to stronger induced dipole-dipole interactions and higher boiling points
why do alkanes have a low reactivity
- high bond enthalpies of the C-C and C-H bonds
- low polarity of the sigma bonds
fuel definition
releases heat energy when burnt
complete combustion of alkanes
- In excess oxygen alkanes will burn with complete combustion
- highly exothermic
- products are CO2 and H2O
incomplete combustion of alkanes
- in a limited amount of oxygen, incomplete combustion occurs
- produces CO or C
- produces less energy per mole than complete combustion
explain the toxicity of carbon monoxide
- toxic to humans as CO can form a strong bond with haemoglobin in red blood cells
-this is a stronger bond than that made with oxygen and so it prevents the oxygen attaching to the haemoglobin
cracking definition
conversion of large hydrocarbons to smaller molecules of by breakage of C-C bonds
economic reasons for catalytic cracking
1.The petroleum fractions with shorter C chains (e.g. petrol and naphtha) are in more demand than larger fractions.
2. To make use of excess larger hydrocarbons and to supply demand for shorter ones, longer hydrocarbons are cracked.
3. The products of cracking are more valuable than the starting
materials (e.g. ethene used to make poly(ethene), branched alkanes for motor fuels, etc.)
catalytic cracking
- conditions
- what does it do
- what is it used for
- why is it useful
slight pressure
high temperatures (450 degrees celsius)
zeolite catalyst
turns straight chain alkanes into branches and cyclic alkanes and aromatic hydrocarbons
used for making motor fuels
Branched and cyclic hydrocarbons burn more cleanly and are used to give
fuels a higher octane number
substitution reactions of alkanes
- conditions
- stages
- mechanism
UV light and a halogen
initiation, propagation, termination
free radical substitution
during initiation, what type of fission occurs
homolytic
alkenes
- formula
- saturated or unsaturated
- shape around carbon atom
- bond angle
- CnH2n
- unsaturated
- trigonal planar
- 120
how do the sigma bonds and pi bonds form in alkenes
- which is weaker
- do pi bonds have low or high electron density and what does this mean?
sigma: two sp2 orbitals overlap to form a single c-c bond
pi: formed by the sideways overlap of two p orbitals on each carbon atom, forming a pi bond above and below the plane of the molecule, they have restricted rotation
pi bond is weaker
high electron density. this means they are vulnerable to attack from electrophiles
stereoisomers definition
compounds with the same structural formula but with a different arrangement in space
what type of isomerism do alkenes display
- why does this isomerism exist
E-Z stereoisomerism
- due to restricted rotation around the C=C double bond
when do E-Z stereoisomers arise
- when there is restricted rotation around the C=C double bond
- there are two different groups/atoms attached to both ends of the double bond
when does cis/trans isomerism occur
when two of the substituent groups are the same
why are alkenes reactive
due to the relatively low bond enthalpy of the pi bond
alkenes + hydrogen
- forms?
- reagent?
- conditions?
- type of reaction?
- alkane
- hydrogen
- nickel catalyst
- addition
why do alkenes undergo electrophilic addition reactions
- double bond has high electron density
- this attracts electrophiles
electrophile definition
electron pair acceptor
alkenes + bromine/chlorine
- forms
- reagent
- conditions
- mechanism
- type of reagent
- type of bond fission
- dihaloalkane
- bromine/chlorine
- room temp
- electrophilic addition
- electrophile, Br+
- heterolytic
hydrogen halide + alkene
- forms?
- reagent
- conditions
- mechanism
- type of reagent
- haloalkane
- HCl or HBr
- room temp
- electrophilic addition
- electrophile, H+
what is markownikoff’s rule
the halogen will be added to the carbon with the fewest hydrogens attached to it
alkenes + steam
- forms?
- reagent
- conditions
- type of reaction
- alcohols
- steam
- high temp (300-600 celsius), high pressure (70atm), H3PO4 catalyst
- hydration
why are poly(alkanes) unreactive
due to the strong C-C and C-H bonds
what are the industrial importances of alkenes
- the formation of polymers from ethene based monomers
- manufacture of margarine by catalytic hydrogenation of unsaturated veg oils using hydrogen and a Ni catalyst
how to deal with waste polymers
- separation and recycling: waste is sorted and then each type can be recycled by melting and remoulding
- feedstock for cracking
- combustion for energy production: Waste polymers can be incinerated and the heat released can be used to generate electricity. Combustion of halogenated plastics (ie PVC) can lead to
the formation of toxic, acidic waste products such as HCl. Chemists can minimise the environmental damage of this
by removing the HCl fumes formed from the combustion
process.
alcohols general formula
CnH2n+1OH
why do alcohols have low volatility
due to their ability to form hydrogen bonds between alcohol molecules
explain the solubility of alcohols
smaller alcohols are soluble as they can form hydrogen bonds with water
the longer the carbon chain, the less soluble the alcohol
uses of ethanol and methanol
ethanol: used as a solvent in the form of methylated spirits
methanol: used as a petrol additive to improve combustion, also used as a feedstock in the production of organic chemicals
complete combustion of alcohols
- burn in excess oxygen producing CO2 and H20
partial oxidation of primary alcohols
- forms?
- reagent
- conditions
- observation
-aldehyde
- potassium dichromate (VI) solution and dilute H2SO4
-warm gently and distil
- orange dichromate ion (Cr2O72-) reduces to the green Cr3+ ion
full oxidation of primary alcohols
- forms?
- reagent
- conditions
- observation
- carboxylic acid
- potassium dichromate (VI) solution and dilute H2SO4
- excess of dichromate, heat under reflux
- orange dichromate ion (Cr2O72-) reduces to the green Cr3+ ion
what can be done to improve the yield in distillation
why does the condenser go against gravity in distillation
collection flask can be cooled in ice
allows more efficient cooling and prevents back flow of water
reflux technique
- when is it used
- why don’t we seal the end of the condenser
- why are anti-bumping granules used
- when heating organic reaction mixtures for long periods. The condenser prevents organic vapours from escaping by condensing them back to liquids
- to prevent vigorous, uneven boiling by making small bubbles form
oxidation of secondary alcohols
- forms
- reagent
- conditions
- observation
- ketone
- potassium dichromate (VI) solution and dilute H2SO4
- excess of dichromate, heat under reflux
- orange dichromate ion (Cr2O72-) reduces to the green Cr3+ ion
why can’t tertiary alcohols be oxidised
as there is no H atom bonded to the carbon with the OH group
dehydration reaction definition
removal of a water molecule from a molecule
reaction of alcohols with dehydrating agents
- forms
- reagents
- conditions
- role of reagent
- type of reaction
- alkene
- concentrated sulfuric or phosphoric acid
- warm under reflux
- dehydrating agent/catalyst
- acid catalysed elimination
substitution reactions of alcohols
- forms
- reagents
- haloalkane
- concentrated sulfuric acid and a sodium halide eg NaCl
nucleophile definition
electron pair donor attracted to low electron density
what does the rate of nucleophilic substitution reactions depend on
- the strength of the C-X bond
- Iodoalkanes are the fastest, fluoroalkanes are the slowest
hydrolysis of haloalkanes
- forms
-reagent
- conditions
- mechanism
- type of reagent
- alcohol
- potassium or sodium hydroxide
- heat under reflux, in aqueous solution
- nucleophilic substitution
- nucleophile, OH-
hydrolysis definition
the splitting of a molecule by water
comparing the rate of hydrolysis reactions
- add what
- what forms
- aqueous silver nitrate is added to a haloalkane and the halide leaving group combines with a silver ion to form a silver halide precipitate
- the quicker the precipitate forms, the faster the substitution reaction and the more reactive the haloalkane
- iodoalkane forms a precipitate first as the C-I bond is the weakest
CFC’s
- why have they been banned
- why are they still a concern
- what is being used instead
- toxicity of the haloalkanes and their detrimental effect on breaking down the ozone layer
- they are still entering the atmosphere from disused items and being used by some countries, they have a long lifetime in the atmosphere
- HFC’s are now used as they do not contain the C-Cl bond
ozone
- how is it formed
- equation
- UV light causes an O2 molecule to split into free radicals, when the free radical hits another O2 molecule, ozone forms
O2 + UV-light = O+O
O+O2 = O3
ozone depletion equation
O3 + ultraviolet light = O2 + O
destruction of the ozone layer
- what causes it
- equations
- radicals from CFC’s, and NOx from thunderstorms or aircraft
- the chlorine free radical atoms catalyse the decomposition of ozone due to these reactions because they are regenerated.
Cl* + O3 = ClO* + O2
ClO* + O* = O2 +Cl*
overall equation
O3 + O* = 2O2
nitrogen oxide radicals formed from thunderstorms or aircraft which also break down the ozone layer:
NO + O3 = NO2 + O2
NO2 + O* = O2 + NO
overall equation
O3 + O* = 2O2
how to purify an organic liquid
- put the distillate of impure product into a separating funnel
- wash product by adding either
- sodium hydrogencarbonate solution , shaking and releasing the pressure from CO2 produced.
- Saturated sodium chloride solution - Allow the layers to separate in the funnel, and then run and
discard the aqueous layer. - Run the organic layer into a clean, dry conical flask and add three spatula loads of drying agent (e.g. anhydrous sodium sulfate, calcium chloride) to dry the organic liquid. When dry the organic liquid should appear clear.
- Carefully decant the liquid into the distillation flask.
- Distil to collect pure product
Sodium hydrogencarbonate will neutralise any remaining reactant acid.
Sodium chloride will help separate the organic layer from the aqueous layer
The layer with lower density will be the upper layer. This is usually the organic layer
the drying agent should be:
- insoluble in the organic liquid
- not react with the organic liquid
the greenhouse effect
- what substances are greenhouse gases
- what is the greenhouse effect of a given gas dependent on
- why have concentrations of CO2 risen recently
- CO2, CH4, H20
- its atmospheric concentrations and its ability to absorb IR and its residence time
- due to increasing burning of fossil fuels
what can IR be used for
- Modern breathalysers measure ethanol in the breath by analysis using infrared spectroscopy
- monitoring gases causing air pollution eg CO and NO from car emissions
describe the bromine test for alkenes and alkanes
alkanes = bromine water remains brown
alkenes = bromine water decolourises
whats an observation that may show carbon is being formed in incomplete combustion
a sooty/smoky flame
which alkanes are more likely to undergo incomplete combustion
longer chain alkanes as they require more oxygen to fully burn completely
explain why the C-H bond in the alkane does not break in the initiation step instead of the C-Cl bond
it needs more energy to break than is available from the UV light
what does a hydrocarbon burning with a yellow flame indicate
incomplete combustion
explain the consequences of CO
- toxic
- as it has a higher binding affinity for haemoglobin than oxygen
- prevents oxygen being transported around the body/ co2 being removed
- odourless and colourless
explain the effect of increasing the intensity of UV light on the reaction between methane and chlorine
- increases the rate
- more energy supplied to break C-Cl covalent bonds
- so more Cl radicals formed
which type of reaction has the greatest atom economy
addition
what is the purpose of the thermometer in reflux
to check the purity of the distillate
what can distillation be used to separate
substances with different boiling points
name the two layers that form in a separating funnel
aqueous and organic layer
suggest two ways that the position of the organic layer in a separating funnel can be determined
- adding water
- the layer that does not get any bigger is the organic layer
- using density data
state the chemicals that are often used as drying agents and how they are removed from the organic liquid
- anhydrous inorganic salts
- removed by filtration or decanting
what is meant by the term fingerprint region on an infrared spectrum
- between 500-1500cm-1
- used for comparison against known compounds
why are molecules of oxygen, chlorine and hydrogen inactive in infrared spec
they do not have a permanant dipole
write the equation for the formation of the molecular ion of octane
C8H18 = C8H18+ +e-
explain how a breathalyser works
- passing infrared radiation through the sample
- detecting and measuring the levels of ethanol within the sample
which type of reaction has the greatest atom economy
addition
what is the reason for heating under reflux
to prevent any substances from escaping
Suggest the general formula for a carboxylic acid
CnH2nO2
What is the general formula of alkyl groups?
CnH2n+1
advantage of using combustion as a method of of polymer disposal
energy production
Describe one difference between the σ bond and the π bond.
σ bond is between bonding atoms/nuclei AND π bond is above
and below the bonding atoms / nuclei
σ bond is between bonding atoms/nuclei AND π bond is above
and below the bonding atoms / nuclei
Describe how HCl is removed from the waste gases produced.
HCl gas is passed through an alkali/ carbonate
