Alkanes, petroleum, haloalkanes, mechanism
What are mineral oil/ lubricating oil used for?
Lubricating oil
what happens if you use a mixture of water and ethanol as solvent for reaction of halogenoalkane with NaOH/KOH under reflux?
1) Both nucleophilic substitution reaction and elimination will occur 2) You'll get alkene and alcohol
How is global warming caused?
1) Burning fossil fuels produces carbon dioxide 2) Carbon dioxide is a green house gas: GHG in atmosphere absorb infared energy (heat) + emit some energy they absorb, back onto earth called greenhouse effect 3) By increasing amount of CO2 in atmosphere, we make earth warmer. aka GLOBAL WARMING
What is the synthesis of chloromethane? (PROPAGATION)
1) Cl* attacks methane molecule: Cl* + CH4 --> *CH3 +HCl 2)Then, methyl free radica attack another Cl2 molecule: *CH3 + Cl2 --> CH3Cl + Cl* The new Cl* can attach another CH4 and so on until all Cl2 / CH4 used up
How is ground level ozone formed?
1) Engines dont burn ALL the fuel molecules --> some come out as UNBURNT HYDROCARBONS 2)These hydrocarbons react with nitrogen monoxide in presence of SUNLIGHT to form ground level ozone (O3) unburnt hydrocarbon + NO (UV sunlight) ---> O3
how are free radicals formed?
1) Free radicals form when covalent bond SPLITS EQUALLY, 2) giving one electron to each species 3) The unpaired electron makes them REACTIVE 4) Dot represents unpaired electron
What alternatives have chemist produced to CFCs?
1) alternative to CFCs are HCFC (hydrochlorofluorocarbons) and HFCs ( hydrofluorocarbons), less dangerous 2) most aerosol replaced by pump spray or use nitrogen as propellant 3) use ammonia or hydrocarbons as coolant gas in fridges 3) CO2 used to make foamed polymers
State features of homologous series of compounds
1) chemically similar / chemically same/ react in the same way 2) same functional group 3) differ by CH2 4) gradual change in physical properties as the relative molecular mass increases (boiling point gradation) 5) same general formula
Crude oil is separated into fractions by fractional distillation. Outline how different factions are obtained by this process?
1) crude oil is heated to vaporise 2) vapour passed into tower/ column 3) Top of tower is cooler than bottom 4) Fractions separated by boiling point/ low BP at top/ condense at different temperature
What are benefits of using zeolite catalyst for catalytic cracking?
1) cuts cost because reaction can be done at lower temperature and low pressure 2) save time—-> because catalyst speeds up the rate of reaction
Outline the essential features of the factional distillation of crude oil that enables the crude oil to be separated into fractions
1) fraction/ hydrocarbons separated depending on boiling point 2) Boiling point depends on size of molecule/ Mr/ chain length 3) Temperature gradient in tower or column/ cooler at top of column/ vice versa 4) higher boiling point/ larger or heavier molecules at bottom of column/ vice versa
what are the 3 main pollutants from vehicle exhausts? what removes these pollutants from exhaust?
1) nitrogen oxides (Nox) 2) unburnt hydrocarbons 3) carbon monoxide REMOVED BY CATALYTIC CONVERTER
How is the ozone formed?
1) oxygen broken down into two free radicals by ULTRAVIOLET LIGHT: O2 + hv—> O * +O * 2) The free radicals attack another oxygen molecule forming ozone O2 + O * —> O3
how can sulfur dioxide be removed from power station flue gas before it gets into the atmosphere?
1) powdered calcium carbonate (calcium) or calcium oxide is mixed with water to make alkaline slurry 2) when flue gas mix w/ alkaline slurry, the acidic sulfur dioxide react with calcium compounds to form harmless salt (calcium sulfate) CaO (s) + sO2 (g) --> CaSO3 (s)
how is sulfur dioxide formed from car engines/ power stations?
1) some fossil fuels contain sulfur 2) When burnt, e.g. in car engines + power stations, sulfur reacts to form SULFUR DIOXIDE (SO2)
Why is it good to heat mixture under reflux?
1) when you heat under reflux, u use equipment that stops vapour escaping from reaction mixture
elimination reaction of 2-bromopropane and in ethanolic condition
1)forms propene water and :Br- 2) :OH- acts as a BASE and takes proton, H+ from carbon (adjacent to halogen) making water 3) The carbon has spare pair of electrons, so forms double bond with middle carbon 4) To make double bond, middle carbon has to detach of Br, leaving it as :Br- ion
What is a free radical?
A free radical is a particle with an unpaired electron
What is the synthesis of chloromethane? (TERMINATION)
All the possible free radical combinations are cancelled out Two free radicals put together, make stable molecule + form COVALENT BOND *CH3 + Cl* —> CH3Cl *CH3 + *CH3 —> C2H6 Cl* + Cl* —> Cl2
What is a nucleophile?
An electron pair donor It donates electrons to somewhere without enough electrons: E.g, :CN- (put dash on top of C) cyanide ion :NH3 ammonia :OH- (out dash on top of O) hydroxide ion
What do nucleophiles attack?
Attacks delta positive carbon It donates electrons to somewhere without enough electrons
Why does each fraction condense at different temperatures?
Because boiling point of alkanes increase as molecules get bigger Each fraction condenses at different temperature
Fractional distillation separates hydrocarbons. What property are they separated by?
Boiling point
How is carbon monoxide removed from exhaust gas?
By catalytic converters on cars
How is crude oil separated?
By fractional distillation
What are the reactivity of halogenoalkanes?
C-F is strongest - has highest bond enthalpy So fluroalkanes undergo nucelophilic subsitiution MORE SLOWLY than other halogenoalkanes C- I is weakest- as low bond enthalply So easier to break Faster substitution as you go down halogen, as bond enthalpy decrease (bonds get weaker) STRONGEST———-> WEAKEST C-F , C-Cl , C-Br , C-I
how does catalytic converter on cars remove these pollutants from exhaust? (unburnt hydrocarbons, nitrogen monoxide)
C2H8(g) + 5O2 (g) --> 3CO2 (g) +4H2O (g) 2NO(g) --> N2 (g) + O2 (g) 2NO (g) + 2CO (g) --> N2 (g) + 2CO2 (g)
How does carbon monoxide affect haemoglobin?
CO binds to the same site on haemoglobin in RBC as oxygen molecules So oxygen can't be carried around the body
What wax, grease used for from crude oil fractions?
Candles, lubrication
When you burn alkanes in COMPLETE OXYGEN, what do u get?
Carbon dioxide and water
What are chlorofluorocarbons?
Chlorofluorocarbons (CFCs) are halogenoalkanes mo,exiles where all the hydrogen atoms are replaced by chlorine and fluorine FOUND: fire extinguisher, fridges
What are the conditions of catalytic cracking? What does it produce?
Conditions: 1)high temperature 2) low pressure 3) uses zeolite catalyst Mostly produces: Aromatic hydrocarbons and alkanes (needed to produce motor fuels)
What are the environmental problems of CFCs
Damage the ozone layer
What is gas oil/ diesel used for from crude oil fractions?
Diesel fuel, central heating fuel
What is petrol used for from crude oil fractions?
Fuel for cars
why is ground level ozone dangerous?
Ground level ozone... 1) irritates people's eyes 2) aggravates respiratory problems 3) cause lung damage
What are halogenoalkanes?
Halogenoalkanes are alkanes with at east one halogen atom in place of hydrogen
How is there polarity in halogenoalkanes alkanes?
Halogens More ELECTRONEGATIVE than Carbon So carbon- halogen bonds polar The halogen atoms WITHDRAWS ELECTRON DENSITY FROM CARBON FORMS: Delta positive carbon, delta negative chlorine
What are amines?
Has the structure R3N R can be hydrogen or another group In amines, nitrogen ALWAYS HAS LONE PAIR
What happens to the hydrocarbon with the lowest boiling point?
Hydrocarbon with the lowest boiling point don't condense They are drawn off as gases at top of the column
How do CFCs (chlorofluorocarbons) break up the ozone?
INITIATION: 1)chlorine free radical formed when C-Cl broken by ultraviolet radiation (UV) CCl3F—> * CCl2F + * Cl PROPOGATION: 2) ozone broken down Cl * + O3 —> O2 + ClO * ClO * + O3 —> 2O2 + Cl * OVERALL RXN: 2O3 —> 3O2 Cl * is catalyst because doesn't get used up
Why is catalytic cracking of crude oil commercially important?
Identify shortfall in supply - e.g. petrol / small molecules —> more in demand (1) Higher value products OR more useful products (1)
What is the synthesis of chloromethane? (SUBSTITUTION)
If CHLORINE IN EXCESS, hydrogen atoms on methane will eventually be replaced by chlorine. 1) CH4 + Cl2--> CH3Cl + HCl 2) CH3Cl + Cl2 --> CH2Cl2 + HCl 3) CH2Cl2 + Cl2 --> CHCl3 + HCl 4) CHCl3 + Cl2 --> CCl4 + HCl BUT if METHANE IN EXCESS, chlorine will be used up quickly + product will be mostly chloromethane CH4 + Cl2--> CH3Cl + HCl
What happens as the crude oil vapour goes up fractionating column?
It gets cooler, creating a temperature gradient.
What is kerosene used for crude oil fractions?
Jet fuel, petrochemicals, central heating fuel
Why do we crack hydrocarbons?
Less popular heavier fractions are cracked, to make light fractions which are MORE USEFUL AND IN DEMAND e,g. Light fractions are naptha and petrol Long chain alkanes are broken into smaller hydrocarbons (including alkenes)
What are the uses of gases from oil fraction? C1-C4
Liquefied petroleum gas or camping gas
What is the synthesis of chloromethane? (INITIATION)
Methane and chlorine will only react when exposed to UV light to form CHLOROMETHANE *Note- put UV on TOP OF ARROW OVERALL: CH4 +Cl2 + (UV) ---> CH3Cl + HCl 1) INITIATION: free radicals prodcued sunlight provides enough energy to break Cl-Cl bonds (aka photo-dissociation), Cl2 +(UV) ---> 2Cl* Bond splits equally + each atom gets one electron each. Cl* highly reactive cuz of unpaired electrom
Why is cracking important?
More useful / needed fuels / products OR implied OR more valuable products OR qualified demand exeeds supply OR to produce motor fuels OR petrol OR cycloalkanes OR aromatic hydrocarbons OR balanced alkanes OR smaller molecules OR alkenes
Give two main types of product obtained by catalytic cracking
Motor fuels Aromatic hydrocarbons Branched alkanes / hydrocarbons Cycloalkanes
What does curly arrow show?
Movement of electron
what type of reaction occurs when you react halogenoalkanes with water and NaOH/KOH under reflux? in aqueous conditions
Nucleophilic substitution forms alcohols you'll get a little bit of alkenes, not a lot :OH- acts as NUCLEOPHILE (d)onates e- to δC
What is a catalytic converter made of?
Platinum/ rhodium/ palladium
What is naphtha used for from crude oil fractions?
Processed to make petrochemicals
What do you get if alkane undergoes incomplete combustion?
Produces carbon (soot) and carbon monoxide gas or as well as CO2
What is a photochemical reaction?
Reactions that are started by light
What is bitumen used from crude oil fractions?
Roofing, road surfacing
What are alkanes?
Saturated hydrocarbons
What are fuel oil used for from crude oil fractions?
Ships, power stations
What are large hydrocarbons cracked into?
Smaller Alkanes AND alkenes
What is cracking?
The breaking down of long-chain alkanes into alkenes and shorter-chain alkanes/ smaller hydrocarbons
Why doesn't the largest hydrocarbon vaporise in fractional distillation?
The largest hydrocarbon doesn't vaporise at all because the boiling points are too high
Why is the ozone layer important?
The ozone layer protects us from harmful ultraviolet rays from the sun, by ABSORBING IT Ultraviolet radiation can cause sun burn or skin cancer
What are the two types of cracking?
Thermal and Catalytic cracking
What are the conditions of thermal cracking?
Thermal cracking Uses: 1) high temperature 2) high pressure 3) produces mostly alkenes alkenes used to make valuable products like polymers (Ethernet—> polyethene)
What are alkanes used for?
Used for fuels
what happens if sulfur dioxide gets into the atmosphere? what are the consequences?
acid rain consequence of acid rain: 1) destroys trees and vegetation 2) corrodes buildings and statues 3) kills fish in lakes
What happens when you warm halogenoalkane with hydroxide ions dissolved in ethanol, not water under reflux?
an ELIMINATION REACTION forms an ALKENE this occurs because :OH- acts as a BASE- removes hydrogen from halogenalkane
how is nitrogen monoxide produced in car engines?
nitrogen monoxide produced when: *HIGH PRESSURE AND HIGH TEMP in car engine *cause nitrogen and oxygen atoms from air to react together *Nitrogen monoxide can react further to produce nitrogen dioxide N2(g)+O2(g)→2NO(g). 2NO(g)+O2(g)→2NO2(g).
What is meant by the term fuel?
release (heat) energy (when burned) (1) OR provides a (useable form of) energy OR is a source of energy
