topic 6 Flashcards
what is a general formula
algebraic formula that can be applies to the chemicals in the family
eg. CnH2n+2 alkanes
what is the molecular formula
actual number of atoms in a molecule
eg. ethane C2H6
what is the empirical formula
simplest whole number ratio of atoms in a compound
eg. ethane CH3
what is the structural formula
arrangement of atoms without showing all the bonds
eg. butan-1-ol CH3CH2CH2CH2OH
what is the skeletal formula
show bonds of carbon skeleton only
hydrogen and carbon not shown but functional groups are
what is the displayed formula
show arrangement of atoms showing all the bonds and atoms in the molecule
what is the homologous series
same functional group and general formula
how to name a molecule
- find length of stem by counting longest continuous chain of carbons
meth eth prop but pent hex hept oct non dec - functional group tells you ending of name
- number the carbon chain so functional group sits on the lowest number
- place number before suffix
- any side chains and less important functional groups are written as prefixes in alphabetical order
what is polymerisation
joining smaller monomers together to form a long chain
what is an addition reaction
joining molecules together to form longer ones
what is a hydrolysis reaction
splitting molecules into 2 using OH- or H+ to form a H2O molecule
what is a substitution reaction
replacing one atom with another on a molecule
what is reduction
when a species gains an electron in a reaction
what is oxidation
when a species loses electrons in a reaction
what is an elemination reaction
some atoms break away from larger molecule
what do arrows on mechanisms show
movement of electrons
what is nucleophilic substitution
primary halogenoalkanes and aq potassium hydroxide to make alcohols
amines made by reacting ammonia
what is radical substitution
reacting halogens to make alkanes to make halogenoalkanes
what is electrophilic addition
adding hydrogens and hydrogen halides to alkenes to make halogenoalkanes
what is chain isomerism
same molecular formula but different arrangement of the carbon skeleton
eg. pentane and 2-methylbutane
what is positional isomerism
same molecular formula but different position of functional group on carbon skeleton
eg. pentan-1-ol and pentan-2-ol
what is functional group isomers
same molecular formula but different functional group
eg. pent-1-ene and cyclopentane
what are alkanes and general formula
saturated hydrocarbons
Cn H2n+2
cycloalkanes CnH2n
what heterolytic fision
both electrons transfered to one species
for ions
X + and Y-
what is homolytic fission
form radicals
each species gets one electron
x. and Y.
what are the steps of free radical chain reactions
initiation
- radicals are produced normally using vissible light or UV, photochemical reactions
- bond breaks producing 2 radicals
prpagation
- radicals react with non radicals
- new radicals create which react with non radicals
termination
- two radicals react to form non radicals
draw free radical substitution of Cl2 and CH4
initiation
Cl —–Cl —-> Cl. + Cl.
UV
propagation
Cl. + CH4 –> .CH3 + HCl
.CH3 + Cl2 –> CH3Cl + Cl.
termination
Cl. + Cl. –> Cl2
.CH3 + .CH3 –> C2H6
.CH3 + Cl. –> CH3Cl
what happens in fractional distilation
column has temperature gradient
parts of hydrocarbon mixture condense at different temp beacuse of different chain lengths and bp
shorter hydrocatbons at top longer at bottom
what is cracking
heavier fractions can be cracked to higher demand lighter fractions
what is thermal cracking
high temp 1000 degrees and pressure 70atm
products mainly alkenes
make polymers
what is catalytic cracking
high temp 450 degree and slight pressure
zeolite catalyst lowers temp and pressure needed
lowers cost and speeds up process
product mainly aromatic hydrocarbons
how are cyclic and branched alkanes made in reforimg
using straight chain alkanes and platinum catalyst
straight chain alkanes create knocking and explode upon compression
what is the complete combustion of alkanes
form carbon dioxide and water
C4H10 (g) + 6.5 O2 (g) –> 4CO2 (g) + 5H2O (g)
what is the incomplete combustion of alkanes
produce carbon monoxide and carbon (soot)
C4H10 + 4.5 O2 –> 4CO + 5H2O
C4H10 + 5.5O2 –> 2CO + 2CO2 + 5H2O
C4H10 + 2.5O2 –> 4C + 5H2O
what is acid rain
release sulfur dioxide and oxides of nitrogen
sulfur dioxide - fossil fuels contrain sulfur based impurities–> acidic gas reacts with water in atmosphere to produce sulfuric acid
oxides of nitrogen - when nitrogen and oxygen are heated in engine –> dissolve in water in atmosphere to form nitric acid
what do catalytic converters do
found mainly in vehicles to reduce harmful pollutants
convert carbon monoxide oxides of nitrogen and unburnt hydrocarbons to water vapour nitrogen and carbon dioxide
what are fossil fuels
created from dead animals and plants that lived millions of years ago
coal
oil
gas
non renewable
what are the biofuels
bioethanol, biodiesel, biogas
how is ethanol made
sugar cane fermented
what are the disadvantages of biofuels
ecpensive to convert existing petrol engines
land could be used to grow crops
what are the advantages of biofuels
renewable so sustainable
carbon neutral, CO2 absorbed by plant, CO2 given off when burnt
what are alkenes and general formula
unsaturated hydrocarbons
double bond
high electron density so reactive
CnH2n
what is a sigma bond
2 s orbitals overlap
high bond enthalpy
strong electrostatic attraction between shared electrons and 2 nuclei due to high electron density
what is a pi bond
overlap of 2 p orbitals
weaker than sigma as electron density spead out above and below
low bond enthalpy
why are alkenes reactive
double bond has high electron density
4 electrons shared between bond
pi bond has low bond enthalp making it reactive
pi bond sticks out so open to attack from electrophiles
what are stereoisomers
same structural formula but different arrangement of atoms in space
what is e/z isomerism
E- same groups opposite the double bond
Z - same group on same side of double bond
how to name stereoisomers
- label carbonds with double bond 1 and 2
- calculate atomic number of 1st element directly bonded to c=c, atom with highest atomic number given priority
if higher prioritys same sides z
if opposite e
what happens to alkenes in electrophilic addition
attacked by electrophiles - electron pair acceptors defficient in electrons
curly arrow from double bond to E+
what is the test for alkenes and mechanism
decolouration of bromine water
brown to colourless
see flash card
what happens in the hydration of alkenes
alcohols produced
steam and acid catalyst used
ethene + water –> ethanol
how to form diols from alkenes
using acidified potassium manganate (VII)
purple to colourless
ethene —H+/MnO4 - —> ethane-1,2-diol
what happens to alkenes with the addition of hydrogen halides
draw mechanism
form halogenoalkanes
see flash card
what happens when you react hydrogen halides with unsymertrical alkenes and what deterimes how much product is formed
produce 2 different products
amount dtermined by stability of carbocation
tertiary most stable as more electron pushing alkyl groups
draw one repeat unit of propene
see flash card
double bonds broken
square brackets
n
name and describe 3 ways plastics are disposed
landfill - plastics that are too difficult to recyle, too difficult to seperat, not enough plastic to extract to make it economically viable, not sustainable and increasingly expensive
recycle - plastics made from non renewable crude oil, cracked into monomers as organic feedstock or remoulded
incineration - burning to generate electricity, release toxic fumes
what things should be considered when making sustainable polyers
reactants - environmentally friendly and not dangerous
solvents - little and low hazard like water
raw materials - renewable
energy - low as possible, catalyst used
waste - reduce waste products especially toxic and environmentaly harmful
longevity - make product out of a sustainable plastic
what are biodegradable polymers and their advantages
decompose naturally in good supply of oxygen and mositure
made from crude oil fractions and renewable sources
- crude oil not used
- plant bassed polymers degrade and release CO2 which is absorbed by plant again
- over products lifetime they use less energy to make than oil based
how to name halogenoalkanes
- find longest carbon chain that will form the last part of the name
- the names and positions of halogens on molecule come first
fluro- chloro- bromo- iodo- - if you have more than one of the same tupe of halogen prefix with di tri tetra
how do halogenoalkanes react with water
nucleophilic substitution
heat with water
alchol formed and H(Cl)
what happens to the reactivity of halogenoalkanes
more reactive down and hydrolysed fastest
bond strength
halide ions get larger down group leading to weaker bond
how to test reactivity of the halogens
add silver nitrate and ethnol
iodide - first - yellow precipitate
bromide - second - cream precipitate
chloride - third - white precipitate
are primary or tertiary halogenoalkanes more reactive
tertiary more reactive
how do halogenoalkanes react with nucleophiles and why
have a polar bond
attacked by nucleophiles - electron pair donor
attack delta+
how do halogenoalkanes react with hydroxide ions
draw mechanism
conditions - warm aq sodium hydroxide under reflux
R–X + NaOH –> ROH + NaX
produce alcohol
OH- ion
see flash card
how do halogenoalkanes react with cyanide ions
draw mechanism
conditions - warm ethanolic potassium cyanide under reflux
R–X + KCN –> RCN + KX
produce nitrile
-CN ion
see flash card
how do halogenoalkanes react with ammonia
draw mechanism
conditions - heat with ethanoic ammonia excess ammonia
see flash card
how do halogenolakanes react with ethanoic hydroxide ions
conditions - warm ethanoic sodium hydroxide under reflux
OH- acts as a base
produce alkene
see flash flash cards
what are alcohols and genral formula
-OH
CnH2n+1 OH
how to make chloroalkanes from alcohols
react with PCl5 or HCl
ROH + PCl5 –> RCl + HCl + POCl3
ROH + HCl –> RCl + H2O
how to make bromoalkanes from alcohols
substitution
react with halide ion source eg. NaBr and acid catalyst
butan-2-ol + HBr –> 2-bromobutane + H2O
how to make iodoalkanes from alcohols
react with PI3
3ROH + PI3 –> 3RI + H3PO3
what happens in the dehydration of alcohols
alkenes made
acid catalyst used
see flash card
what happens in the combustion of alcohols
produce carbon dioxide and water
C2H5OH + 3O2 –> 2CO2 + 3H2O
what happens in the oxidation of primary alcohols
aldehydes the carboxylic acid
using potassium dichromate K2Cr2O7
see flash card
what happens in the oxidation of secondary alcohols
ketones produced
potassium dichromate
what happens in the oxidation of tertiary alcohols
not oxidised
what is the test for aldehydes and ketones
fehlings or benedicts
aldehydes - blue to brick red
ketone - blue
what is reflux
liebig condenser
hot evaporating substances hit cold condenser they turn back into liquid and return to round bottom flask
what is distillation
separate substances with different bp
lower boiling point - colect in seperate vessel
higher bp - remain in round bottom flask
what is redistilation and separation
redistilation - purify volatile substances
seperation - purify further
