Organic Chemistry Flashcards
organic chemistry
the chemistry of carbon
1C
meth
2C
eth
3C
prop
4C
but
5C
pent
6C
hex
7C
hept
8C
oct
9C
non
10C
dec
C bonds
4
N bonds
3
H bonds
1
O bonds
2
saturated compound
all the chemical bonds between carbons are single bonds
unsaturated compound
at least one of the carbon to carbon bonds is a double or triple bond
aliphatic compounds
contain open (straight or branched) chains of carbon atoms and closed rings of carbon with similar properties
aromatic compounds
contain at least one benzene ring
functional group
a group of atoms which are present in all members of any series, which determines
homologous series
a group of organic compounds with a common functional group and successive members of the series differ in size by CH2
structural isomerism
compounds with the same molecular formula but have differnt structural formula
mirror images
not isomers
molecules that can be easily straightened
not isomers
addition reactions
a molecule has extra atoms added without losing any of its own atoms
substitution reactions
atoms already on a molecule are substituted or replaced by different atoms
hydrocarbons
only has hydrogen and carbon
nomenclature
system of naming
longest chain for alkanes
just the longest carbon chain
longest chain for non alkanes
longest carbon chain containing the functional group
which way to number for alkanes
keep the carbons carrying a substituent as low as possible
which way to number non-alkanes
carbons in functional group kept as low as possible
2 of the same substituent
di
3 of the same substituent
tri
4 of the same substituent
tetra
order to list different substituents
alphabetical
eg. 4-chloro-3-ethyl-3-methylheptane
numbers separted from numbers with a
,
numbers separated from letters by
-
rule 5 for alkene and alkynes only
position of double or triple bond indicated by lower of 2 numbers eg. pent-2-ene
what is boiling point an indication of?
how difficult it is to separate molecules from each other
are hydrocarbons polar or non-polar
non-polar
solubility of hydrocarbons
don’t dissolve in non-polar solvents such as water but do in non-polar eg.cyclohexane
solubility rule
like dissolves like
boiling points of hydrocarbons
weak van der waal forces, low boiling points
Mr of hydrocarbons increases
greater the boiling point
small hydrocarbons at room temp
gases
large hydrocarbons at room temp
liquids
aldehydes and ketones contain what?
carbonyl group
carbonyl group
\
C = O
/
boiling points of aldehydes and ketones and why
higher than hydrocarbons , dipole dipole attraction vs van der waal
solubility of aldehydes and ketones and why
both soluble in water, both have polar ends which are attracted to water by hydrogen bonding
if the aldehydes and ketones have long C-H chains
the nonpolar ends become bigger and more important
large nonpolar end repels water more than the smaller polar end attracts the water so that the larger aldehydes and ketones are insoluble in water
functional group of alcohols
hydroxyl group
hydroxyl group
-O-H-
boiling points of alcohols and why
higher than comparable aldehydes and ketones because of hydrogen bonding
comparable
same Mr
solubility of alcohols and why
very soluble in water, hydrogen bonding
alcohols with large C-H chains
C-H becomes the bigger part, overall molecule gets bigger and non-polar part is now more important than polar. dissolves in cyclohexane and not water
carboxylic acids functional group
carboxylic group
carboxylic group
O
//
- C
\
O - Hboiling points of carboxylic acids and why
highest of all, hydrogen bonding and more sites for hydrogen bonding
summary of boiling points
Carboxylic acids, alcohols, aldehydes and ketones, hydrocarbons (alkanes, alkenes, alkynes)
double H bond, h bond, dipole dipole, van der waal
solubility of carboxylic acids and why
very soluble in water because they undergo hydrogen bonding
when C-H chain gets too long in carboxylic acids
non-polar part more important, dissolves in cyclohexane not water
crude oil
mixture of substances of different Mr
what is refining about
separating the substances from each other
fractional distillation
the heating of crude oil and then separating the various mixtures on the basis of their different boiling points
crude oil is
viscous
crude oil first goes into
a furnace
what goes in the bottom of the steel column
super heated steam
what comes out the bottom of the steel column
residue of tar
what happens in the furnace
it is partially vapourised
bottom of steel column
very hot
top of steel column
coolest part
interior of steel column arranged
in horizontal trays
X’s tray
X can be removed
above X tray
X is liquid and falls down
below X tray
X is gas under pressure and floats up
4 types of petroleum gas
methane
ethane
propane
butane
-CH3
methyl
-C2H5
ethyl
-C3H7
propyl
-C4H9
butyl
2 uses of petroleum gas
domestic bottle gas and LPG
LPG
liquid petroleum gas used in some cars
light gasoline aka
petrol
carbon atoms per molecule of petrol
5-10
use of petrol
for fuel
petrol is mostly
alkanes
carbon atoms per molecule of naptha
7-10
carbon atoms per molecule of something you can use to make petrol
5-10
2 uses of naphtha
petrol and raw materials
4 things naphtha is used as a raw material for
plastics, solvents, fibres, detergents etc
carbon atoms per molecule of kerosene
11-14
2 uses of kerosene
jet engine fuel
home heating
gas oil aka
diesel
carbon atoms per molecule of diesel
14-20
use of diesel
in diesel engines
carbon atoms per molecule of lubricating oil
20-30
use of lubricating oils
lubricating oil
lubricating oils are
viscous
why aren’t lubricating oils used as fuel
not easily vapourised
carbon atoms per molecule of fuel oil
30-35
use of fuel oil
can be made into droplets and used as ship and power station fuel
carbon atoms per molecule of bitumen
> 35
use of bitumen
road tar
smell of methane ethane etc.
odourless but sulphur containing mercaptans added to give a strong smells so leaks easily detected
smell of methane ethane etc.
odourless but sulphur containing mercaptans added to give a strong smells so leaks easily detected
petrol coming from fractioning column
inefficient fuel
what is an inefficient fuel
explodes on compression before spark ignites it
explodes on compression before spark ignites it
auto-ignition
auto-ignition causes
knocking
knocking causes 3
loss of power
engine damage
excessive noise in the car
what causes knocking
straight chain molecules
what prevents knocking
the presence of branched chain molecules
octane rating
the capacity of petrol to burn smoothly
octane rating scale
1-100
0 on octane rating
heptane
100 on octane rating
2,4,4 trimethylpentane
2,4,4 trimethylpentane aka
iso octane
definition of octane number of a fuel
the measure of the tendancy of a fuel to resist knocking
octane number of 97 efficiency
same as 97% 2,4,4 trimethylpentane and 3% heptane
2,4,4 trimethylpentane and heptane
reference substances
4 features of high octane rating fuel
- highly branched molecules
- short alkanes
- cyclical compound
- aromatic molecules
1 highly branched molecule
2,4,4 trimethylpentane
1 short alkane
pentane
1 cyclical compound
cyclohexane `
aromatic molecules
contain benzene
what was put into petrol before
anti-knocking agent
tetra ethyl lead
3 reasons why use of tetra ethyl lead was stopped
lead pollution in air
it’s tendency to poison catalytic convertors
toxicity to human health
4 ways to ensure petrol has a high octane number
isomerisation
reforming
adding oxygenates
catalytic cracking
isomerisation
when straight pentane and hexane with low octane numbers are heated and passed over a catalyst. they break up at and reform at random to give a mixture of straight and branched versions (isomers)
reforming aka
dehydrocyclisation
reforming
use of catalysts to form ring compounds, converted to cycloalkanes such as cyclohexane
2 things happening in reforming
hydrogen is expelled
aromatic compounds are formed
valuble hydrogen made in dehydrocyclisation
piped away
adding oxygenates
3 oxygen containing compunds added to petrol to increase it’s octane number
3 oxygen containing compunds that are added to petrol to increase it’s octane number
methanol
ethanol
MTBE
MTBE
methyl tertiary butyl ether
secondary use of oxygenates
reduce the level of pollutants coming from petrol, especially CO2 gas
catalytic cracking aka
cat cracking
cat cracking definition
the breaking down of long chain hydrocarbon molecules using heat and catalysts into smaller molecules which are more useful
cat cracking is carried out on… and why
kerosine, diesel oil and fuel oil, to obtain shorter molecules of carbon length 5-10 and higher octane rating
2 things cat cracking yields
more molecules with carbons lengths 5-10
smaller molecules such as alkenes
why are more molecules with carbons lengths 5-10 important
petrol can be manufactured
usually highly branched ie. high octane number
why are smaller molecules such as alkenes important?
manufacture of plastics and other chemical products
use of cracking allows chemists to…
use of cracking allows chemists to convert many of the fractions from crude oil for which there is little use
h2 burns readily in O2, what are products?
only H2O
H2 + 1/2 O2 ->
H2O
ΔH =
-242 kj/mole
3 difficulties with hydrogen as a fuel
expensive to produce
very explosive in air
very low density
how is hydrogen produced
electrolysis or steam reforming of methane
steam reforming of methane
burning of fossil fuels
why is very low density a problem
difficult to store
must be stored in high pressure containers
equation for steam reforming of methane to form H2
CH4 + H2O -> 3H2 +CO
equation for hydrogen gas being used in the industrial production of ammonia
N2 + 3H2 -> 2NH3
hydrogen also used in?
the hydrogenation of vegetable oils in margarine production
general formula of alkane
C2 H2n+2
functional group of alkanes
/ - C - / no double carbon bond no triple carbon bond no oxygen
name for alkanes
-ane
first alkane
methane
methane
CH4
ethane
c2H6
general formula of alkenes
CnH2n
functional group of alkenes
carbon to carbon double bond
first alkene
ethene
ethane
C2H4
general formula of alkynes
CnH2n-2
functional group of alkynes
carbon to carbon double bond
first alkyne
ethyne
ethyne
C2H2
alcohol general formula
CxHy-OH
functional group of alcohol
-O-H
first alcohol
methanol
methanol
CH3OH
general formula of aldehydes
CxHyCHO
functional group of aldehydes
O
//
-c
\
Hfirst aldehydes
methanal
methanal
HCHO
general formula of ketones
(CxHy)nCO
functional group of ketones
O
//
C
/ \
first ketone
propanone
propanone
(CH3)2 CO
general formula of carboxylic acids
CxHyCOOH
functional group of carboxylic acids
methanoic acid
methanoic acid
HCOOH
aromatic hydrocarbons contain what
a benzene ring
molecular formula for benzene
C6H6
who proposed the structural formula for benzene and when
kekule in 1865
was kekule correct?
no
first characteristic of benzene that proved kekule wrong?
C-C length
he suggested that there were two different bond lengths but there is only one in benzene, all the bonds are equal
second characteristic of benzene that proved kekule wrong? C=C
kekule’s structure had very reactive C=C bonds, which would suggest it undergo addition reactions
what can tell us that benzene does not have C=C bonds?
2
very unreactive, undergoes substitution reactions
does not decolourise bromine water of KMnO4
how many valence or bonding electrons does carbon have
4 valence or bonding electrons
3 of carbon’s valence electrons in benzene
involved in σ bonds with 2 neighbouring carbon atoms and one hydrogen atom
the 4th valence electron is benzene
exists in an unused p orbital
how many unused p orbitals in benzene
6
how are the 6 unused p orbitals aligned?
perpendicular to the plane of the ring
where are the 6 π bond electrons located?
they are free to move throughout the entire ring so they don’t belong to any carbon
what does it mean that they are free to move throughout the entire ring so they don’t belong to any carbon
they are delocalised
what does the fact that 6 electrons are delocalised give benzene?
extra stability
what does the extra stability account for?
it’s general unreactivity
why should contact with benzene be avoided?
it’s known to be carcinogenic
what is a safer molecule derived from benzene
methyl benzene
what is methyl benzene known for
its a non polar solvent. won’t dissolve in water but will in cyclohexane
the look of a benzene molecule
a flat molecule
bond angle of carbons in benzene
120º
how are aromatic compounds obtained
mostly from the fraction distillation of crude oil
general formula of alkanes
C n H 2 n+2
alkanes, saturated or unsaturated?
saturated
all carbons in alkanes
have 4 single bonds out of them
structure of carbons in alkanes
tetrahedral structure
are alkanes reactive
mostly unreactive
what does the fact that alkanes are mostly unreactive explain
explains why they are widely found in nature
first four alkanes at room temperature
gases
next twelve alkanes at room temperature
liquids
heavier alkanes
waxy solids
where are the waxy solid, heavy alkanes found
in plants
first for alkane gases
methane, ethane, propane, butane
where are the first for alkanes produced
in large quantities in fractional distillation of crude oil
3 properties of the first 4 alkanes
light
colourless
odourless
why are the first 4 alkanes excellent fuels
they combust easily
are the first 4 alkanes reactive
generally unreactive
where can methane also be produced? 2
the anaerobic respiration of decaying organic matter and by farm animals
3 examples of decaying organic matter that produce methane
farm manure
marshes
rice paddy fields
2 uses of methane
a fuel
on an industrial scale, to make H2 gas
make NH3
how is H2 gas made out of methane
it is reacted with high pressure steam
production of NH3
first step in the manufacture of artificial nitrate fertiliser
methane is regarded as
a greenhouse gas that contributes to global warming
chloroalkanes
one or more of the hydrogen atoms in alkane molecules is replaced by a chlorine atom
are chloralkanes saturated or unsaturated
saturated
structure of chloroalkanes
tetrahedral structure
chloroalkanes at room temp
liquids
are chloroalkanes good solvents
excellent solvents
are chloroalkanes polar or non-polar
largely non polar
bp of chloroalkanes
low bp, vaporise off surfaces easily
2 uses of chloroalkanes
dry cleaning clothes
tippex
what is dichloromethane found in
paint stripper
how does dichloromethane work as a paint stripper
acts as a solvent and dissolves old unwanted paint and that it evaporates due to us low boiling point, leaving the dry dissolved paint behind as a flaky surface, easily scraped off
recent concern about chloroalkanes
they cause harm to the ozone layer in the atmosphere `
if there are more than 3 carbons?
they can undergo isomerism
general formula for alkenes
CnH2n+2
functional group of alkenes
C=C
smallest alkene
ethene
alkenes, saturated or unsaturated
unsaturated
smallest 3 alkenes at rt
gases
other alkenes
liquids or soft solids
shape of alkene molecules
planar
why are alkenes planar
2 carbons joined by a double bond
shape of longer carbon chain alkenes e.g. pent-1-ene
has a planar end with the functional group and the other end is tetrahedral
are alkenes reactive
much more reactive than alkanes
why are alkenes much more reactive than alkanes
because the C=C bond is much less stable than the C-C and C-H bonds
double bond consists of
sigma and pi bonds
which is weaker sigma or pi
pi is weaker
why are C=C bonds more reactive than C-C bonds
the weak pi bond breaks easily releasing it’s two bonding electrons to bond with other atoms or groups of atoms
in general, what do addition reactions cause
a change in structure from planar to tetrahedral
how do you prepare an alkene
dehydrate the appropriate alcohol
appropriate alcohol
same number of carbon
preparation of ethene formula
C2H5OH –> C2H4 + H2O
ethanol
C2H5OH
preparation of ethene, what holds the ethanol in place
glass wool
how is the tube placed in the preparation of ethene
horizontally
preparation of ethene, where do you clamp the boiling tube
near its neck
preparation of ethene, what do you add half way along the tube
aluminium oxide
preparation of ethene, how much aluminium oxide do you use
2g
preparation of ethene, how do you push the glass wool into the tube
using a glass rod
preparation of ethene, how do you put the aluminium oxide into the tube
using a spatula
preparation of ethene, how is ethene collected
by the downward displacement of water
preparation of ethene, describe how you heat the tube
just touch the flame onto the alcohol end
preparation of ethene, what happens when the alcohol vapour passes over the aluminium oxide?
its dehydrated
aluminium oxide
Al2O3
preparation of ethene, what do you do at the start when gas starts to come out and why?
let is bubble off for a minute do not collect as it is mostly air
preparation of ethene, how much do you collect
collect about 5 jars of ethene
preparation of ethene, after collecting each jar
put a stopper in
preparation of ethene, after collecting sufficient amount
turn off bunsen burner and immediately disconnect delivery tube to prevent suck back
preparation of ethene, how do you disconnect delivery tube
loosening the clamp and sliding up so that the delivery tube is out of the water
what is suck-back?
where a vacuum occurs in the tube as it cools and draws cold water into the hot boiling tube causing it to splinter and crack
2 tests for unsaturation
bromine water
acidified potassium mangnate
colour change of bromine water
red/orange to colourless
colour change of acidified potassium magnate
purple to colourless
potassium magnate
KMnO4
reaction for production of ethene
elimination reaction
definition of an elimination reaction
a reaction in which a small molecule is removed from a large molecule leaving a double bond behind on the remaining larger molecule
colour of ethene
colourless
smell of ethene
sweet smell
solubility of ethene
insoluble in water, soluble in cyclohexane
how do you test ethene for unsaturation
add some bromine water, stopper an invert (or with acidified potassium magnate)
how do you combust a jar of ethene
apply a lighted wax taper to its mouth
combustion of ethene
burns brightly
what is produced when ethene is burned in air
CO2 is formed
testing burned ethene for CO2
put some lime water in it, stopper and invert. goes milky white
burned ethene turns into
water and carbon dioxide
burned ethene in air equation
C2H4 + 3O2 –> 2CO2 + 2H2O
general rule, organic compounds burn
to form CO2 and H2O
preparation of ethene 3 other precautions
do not let flame directly near ethanol
handle glass wool with gloves
tie back hair, wear goggles, wear a lab coat
why do alkenes undergo addition reactions
because they have a double bond which makes it easy to ‘add on’ items
why are alkanes much less reactive than alkenes or alkynes
they have no C=C bond or C=-C bond to enable addition reactions to occur
substitution reactions in alkanes
much slower to occur
2 catalysts for hydrogenation of ethene
200º and Ni
hydrogenation of ethene equation
C2H4 + H2 —> H2H6
H2H6
ethane
Chlorination of ethene equations
C2H4 + Cl2 —> C2H4Cl2
product from chlorination of ethene
1,2-Dichloroethane
bromination of ethene equation
C2H4 + Br2 –> C2H4Cl2
product of bromination of ethene
1,2-Dibromoethane
colour of bromine
red/yellow
colour of 1,2-Dibromoethane
colourless
why do you never use bromine in the bromination of ethene
it’s too dangerous for the lab, you use bromine water
equation, adding hydrogen chloride to ethene
C2H4 + HCl —> C2H4Cl
catalyst for adding hydrogen chloride to ethene
AlCl3
AlCl3
aluminium chloride
product of adding hydrogen chloride to ethene
1-chloroethane
hydration
addition of water
what is hydration of ethene the reverse of?
production of ethane from ethanol (dehydration of ethanol)
2 catalysts for the hydration of ethene
high temperature and pressure
equation of hydration of ethene
C2H4 + H2O –> C2H4OH
C2H4OH
ethanol
what does polymerisation do to one ethene
turns it into polyethene
what do you not do when drawing polymers
put Hs at the ends, they’re not finished, they are repeating units
1 use of hydrogenation in industry
in the food industry, used to convert some double bonds in vegetable oils (polyunsaturates) to single bonds, changing them from liquid oils to spreadable semi-solids eg.margarine
3 double bonded oils
palm oil
sunflower oil
corn oil
2 saturated fats
dairy and cream
which are thought to be healthier, polyunsaturated fats or saturated fats ?
polyunsaturated fats
how can you make an oil as soft or hard as you want
by controlling the degree of hydrogenation
2 advantages of hydrogenation
healthier unsaturated fats are spreadable
can make fats as soft or hard as required
the product of chlorination of ethene
1,2-Dichloroethane
where is 1,2-Dichloroethane used?
it is the raw material for the production of chloroethene
what is chloroethene
it is a well known monomer used for the production of polychloroethene
common name for chloroethene
vinyl chloride
common name for polychloroethene
poly vinyl chloride (PVC)
word equation for ethene -> PVC
ethene + chlorine -> dichloroethane
loses HCl to make chloroethane. polymerised to become polychoroethene (PVC)
chemical equation for ethene -> PVC
C2H4 + Cl2 -> C2H4Cl2 -> C2H3Cl->
(C2H3Cl)n
what is the function of 1,1,1-trichloroethane
allows 2 reactants to mix together freely. i.e a solvent
addition of bromine (bromination) is
a test for unsaturation
how to be sure of unsaturation after bromination test
do a second test with KMnO4
potassium mangnate
when fruits ripen, what do they produce
ethene
where is ethene also produced and what’s its function
produced artificially in ripening rooms to spped up ripening
why should ripening fruit never be beside flowers
the ethene produced will cause they flowers to ripen and fall off
definition of polymerisation
where many small molecules called monomers join together to give a long polymer
what is high density polythene
polythene where long chains line close to each other and have no branching
2 features of high density polythene
rigid and a high melting point
what is low density polythene
long chains have branching out of them so they cannot lie close together
1 feature of low density of polythene
lower melting point
addition polymerisation
where no tiny molecules are expelled during the process
condensation polymerisation
where tiny molecules are expelled during the process
polymer of ethene
polyethene (polythene)
uses of polyethene
hard and soft plastic depneding if it’s high density or low density
polymer of propene
polypropene (polyproylene)
2 uses of polypropylene
tough plastic
- beer crates
- stacking chairs
thermoplastic vs thermosetting
thermoplastics can be reheated and remoulded many times, thermosetting plastic cannot
general formula of alkynes
CnH2n-2
functional group of alkynes
C≡C (carbon to carbon triple bond)
polymer of chloroethane
polychloroethane (PVC)
2 uses of polychloroethane
doors and windows
raincoats
reactions that alkynes undergo
addition reactions
why do alkynes undergo additiion reactions
because weak pi bonds break easily
2 features of C≡C
strong
highly reactive
smallest alkyne
ethyne
whene ethyne burned in a stream of O2
produces temperatures in excess of 3,000°
what is used for cutting equipment
oxyacetylene
describe how oxyacetylene cutting equipment works
2 separate tanks of ethyne and oxygen are connected through a single outlet and the mixture is burned on exit in a controlled flame to give really high burning temperatures
formula of benzoic acid
C2H5COOH
formula of phenol
C6H5OH
formula for nitrobenzene
C6H5NO2
formula for methyl benzene
C6H5CH3
formula for benzaldehyde
C6H5CHO
how to draw any of the aromatic compounds
draw a circle inside a hexagon and the substituent sticking out of one corner of the hexagon
sub in benzoic acid
COOH
sub in phenol
OH
sub in methyl benzene
CH3
sub in nitrobenzene
NO2
sub in benzaldehyde
CHO
combustion of ethene formula
C2H4 + 3O2 –> 2CO2 + 2H2O
by what action can you make ethyne
by the action of water on calcium dicarbide
describe calcium dicarbide
a grey/ black solid
formula for preparation of ethyne
CaC2 + 2H2O –> Ca(OH)2 + C2H2
CaC2
calcium dicarbide
Ca(OH)2
calcium hydroxide
C2H2
ethyne
how does calcium hydroxide look
cloud white ppt
what does ethyne look like
colourless gas
when ethyne burned in air
a lot of soot produced
when ethyne burned in pure oxygen
no soot produced
preparation of ethyne, what is used to filter out the impurities from the gas
acidified copper sulphate solution
preparation of ethyne, 3 impurities trapped by acidified copper sulphate solution
H2S
NH3
PH3
PH3
phosphine
why do impurities arise from CaC2
it is not purchased pure, but contains impurities that turn into H2S, NH3, PH3 when reacted with water
preparation of ethyne, what gives the gas odour
the impurities
2 things that happen when a jar of C2H2 is burned
- gives off great heat
2. causes a great amount of soot to be formed
what was carbide used for
carbide lamps were used years ago before the invention of batteries
how does a carbide lamp work
water drips slowly onto CaC2 and the C2H2 produced is lit and burns brightly
preparation of ethyne, what can be used to prove that CO2 was produced in the reaction
limewater turns milky
formula for combustion of ethyne with oxygen
2C2H2 + 5O2 –> 4CO2 + 2H2O + heat
why is great heat released when ethyne is burned
high energy carbon to carbon triple bond is broken during combustion
ethene flame
bright yellow flame
ethyne flame
sooty flame
preparation of ethyne, name of flask the water drips into
buchner flask
preparation of ethyne, what does the water drip from
a tap funnel
preparation of ethyne, what apparatus is used to collect the gas
a glass tube and a beehive stand
preparation of ethyne, where does the calcium carbide go
into the buchner flask
preparation of ethyne, what do you use to transfer the calcium carbide into to buchner flask
a spatula
preparation of ethyne, why do you never touch the calcium carbide
the moisture on you hand might start the reaction
preparation of ethyne, how fast do you let water flow
only in drips
preparation of ethyne, what happens to the flask contents when the water starts to drip
becomes cloudy white
preparation of ethyne, what happens to the flask when gas starts to be produced
get very hot
preparation of ethyne, what should you do with the first few jars and why
discard them, they are most likely just air
preparation of ethyne, how many jars do you collect
about 4 or 5
how do you test for ethyne gas
light the jar contents, should burn with a pop
preparation of ethyne, how do you stop the production of gas
stop the flow of water
preparation of ethyne, why do you dismantle the apparatus and empty the contents before before testing the ethyne
because we will be using a lighted taper on one of the jars and ethyne forms an explosive mixture with air
preparation of ethyne, smell of ethyne if impurities get through
unpleasant smell
is ethyne soluble in water and how do we know
no
collected by the downward displacement of water
where do you burn a jar of ethyne
in a fume cupboard only
what is the soot produced when during ethyne
carbon soot
3 characteristics of ethene flame
less sooty/clear, less bright, bluish flame
bromination test on ethyne
add a very small amount of bromine water into a test tube of ethyne gas, stopper and shake well (yellow/red -> colourless)
KMnO4 test on ethyne
same as bromine water. colour change purple -> colourless
3 precautions of preparation of ethyne
keep naked flames away from ethyne, don’t touch calcium dicarbide , do all tests on ethyne in a fume cupboard
reaction mechanism
a step by step account of how a reaction occurs
what drives a substitution mechanism
driven by free radicals
substitution reaction aka
free radical substitution
free radical
a group of atoms, or a single atom which are very reactive due to having one unbounded electron
free radical substitution reaction, chemical equation
CH4 + Cl2 -> CH3Cl + HCl
3 stages of free radical substitution reaction,
initiation stage
propagation stage
termination stage
free radical substitution reaction, initiation stage
UV light is needed to start the reaction
photochemical reaction
depends on light
what can prove that our free radical substitution reaction is a photochemical reaction
it doesn’t occur in the dark
free radical substitution reaction, what is the splitting of Cl2 into 2 free radicals Clº and Clº
homolytic fission
homolytic fission
when a chemical bond breaks and each of the pieces retains one of the originally bonded electrons
free radical substitution reaction, when and how does the propagation stage start
begins automatically when initiation stage is over
free radical substitution reaction, 2 different repeating reactions in propagation stage are driven by
2 free radicals:
Clº and CH3º
free radical substitution reaction, propagation stage, reaction driven by Clº
Clº + CH4 -> CH3º + HCl
free radical substitution reaction, propagation stage, reaction driven by CH3º
CH3 + Cl2 -> CH3Cl + Clº
free radical substitution reaction, propagation stage continues in a
chain reaction
free radical substitution reaction, propagation stage continues until
when one of the reactants starts to get scarce
free radical substitution reaction, if Cl2 gets scarce reaction
CH3º + CH3º -> C2H6
free radical substitution reaction, if CH3 gets scarce
Clº + Clº -> Cl2
free radical substitution reaction, if both Cl2 and CH3 get scarce
CH3º + Clº -> CH3Cl
free radical substitution reaction, 3 proofs to show that the mechanism proposed is correct
Presence of traces of C2H6
addition of tetra methyl lead lead which decomposed into free radicals and speeds up the reaction
will not occur without UV light
chain reaction
a reaction, once started, can only be stopped when at least one of the reactants is completely used up
free radical substitution reaction another example
chlorination of ethane
free radical substitution reaction, 2 free radicals driving the chlorination of ethane
ethyl or CH3CH2
free radical substitution reaction no.2chlorination of ethane, what is formed in the termination stage rather than ethane
butane
free radical substitution reaction, 2 free radicals driving the chlorination of ethane, what can be used to speed up the reaction
tetra ethyl lead
