Alkanes Flashcards
What is the general formula for alkanes?
CnH2n+2
What is the functional group?
C-C single bonds
Are they saturated or unsaturated hydrocarbons?
Saturated Hydrocarbons (contain hydrogen and carbon ONLY)
How do they differ?
by CH2
Are they soluble or insoluble in water?
Insoluble in water
Are they reactive or unreactive?
Unreactive
What is the trend as you go down the homologous series?
As you go down the homologous series, the boiling point INCREASES. This is because as the chain length increases there is more surface area for intermolecular forces of attraction which needs to be overcome (van der vaals molecular forces of attraction)
What is cracking?
Cracking is the name given to breaking up large hydrocarbons into smaller and more useful bits.
How is cracking achieved?
This is achieved by using high pressures and temperatures without a catalyst or lower temperatures and pressures in the presence of a catalyst
Give some facts about cracking (reference temperature and pressures)
♡ Cracking breaks up large hydrocarbon molecules into smaller more useful bits. ♡This is achieved using high temperatures and high pressures without a catalyst or ………………. ♡ low temperatures and low pressures with a catalyst
Give the source of large hydrocarbon molecules
♡The source of large hydrocarbon molecules is often in the naphtha fraction or the gas oil fraction from the fractional distillation of crude oil (petroleum). ♡These fractions are obtained from the distillation process as liquids but are re-vapourised before cracking
How are hydrocarbon molecules broken up?
♡ In a fairly random way to produce mixtures of smaller hydrocarbons some of which have carbon-carbon double bonds.
Write the reaction of the hydrocarbon C15H32
C15H32’——> 2C2H4 + C3H6 + C8H18 ethene propene octane . The ethene and propene are important materials for making plastics or producing other organic chemicals. The octane is one of the molecules found in petrol (gasoline).
Name the catalyst for Catalytic cracking:
Zeolites
What are zeolites?
These are complex aluminosillicates, and are large lattices of aluminium, silicon and oxygen atoms carrying a negative charge. They are associated with positive ions such as sodium ions.
In catalytic cracking what are the temperatures and pressures used?
The alkane is brought into contact with the catalyst at a temperature of 500°C and moderately low pressures
What are the zeolites used for and what do they produce?
♡ to give high percentages of hydrocarbons with between 5 and 10 carbon atoms which is useful for peteol ♡ Produces high proportions of branched alkanes and aromatic hydrocarbons luke benzene
What is involved in catalytic cracking?
An ionic intermediate
What are the structures of the zeolite catalyst?
The zeolite catalyst has sites which can remove a hydrogen from an alkane togther with the two electrons which bound it to the carbon . ♡ Taht leaves the carbon atom with a positive charge. ♡ Ions like this are called carbonium ions
What are the temperatures and pressures used in thermal cracking?
High temperatures (450°C-750°C) and pressures (upto about 70 atmospheres) are uses to break the large hydrocarbons into smaller ones.
Describe thermal crackings mixtures of products
Thermal cracking gives mixtures of products containing high proportions of hydrocarbons with double bonds - alkenes
Give one way on which thermal cracking is different from catalytic cracking
Thermal cracking doesn’t go via ionic intermediates like catalytic cracking. ♡ instead carbon-carbon double bonds are broken so tat each carbon atom ends up with a single electron. ♡ Free radicals are formed
C8H18 is obtained by the catalytic cracking of suitable heavy fractions. State what is meant by the term cracking and name the catalyst used in catalytic cracking.
Cracking is breaking up large hydrocarbon molecules into smaller more useful ones. the catalyst used is zeolite.
Write an equation to show how one molecule of C14H30 is cracked to form one molecule of C8H18 and one molecule of another hydrocarbon
C14H30——> C8H18 + C6H12
Explain why oil companies need to crack “suitable heavy fractions “
Oil companies need to crack suitable heavy fractions to make long hydrocarbon chains into smaller more useful ones which are more useful eg. Petrol which are more information demand and valuable
State the type of cracking that produces a high percentage of alkenes. State the conditions needed for this type of cracking
♡Thermal cracking ♡ Conditions : High temperatures and high pressures
Explain the main economic reasons why alkanes are cracked.
You can make other products and sell them
One molecule of C9H20 can be cracked to form one molecule of pentane and one other product. Write an equation to represent this.
C9H10—–> C5H12 + C4H8
One molecule of C9H20 can be cracked to form one molecule of pentane and one other product. Write an equation to represent this.
C9H10—–> C5H12 + C4H8
One molecule of C9H20 can be cracked to form one molecule of pentane and one other product. Write an equation to represent this.
C9H10—–> C5H12 + C4H8
The cracking of one molecule of a compound, x, produces pent-1-ene ethene and butane in a 1:2:1 mole ratio. Deduce the MF of x and write an equation for the reaction
X—> C5H10 + 2C2H4 + C4H10 so that = C13H28 so equation is C13H28—-> C5H10 + 2C2H4 + C4H10
What is a polymer?
Made from many monomers or repeated sub units eg. ethene and propene
Describe the fractional distillation process and how it’s different from distillation
Fractional distillation is a process which converts crude oil into useful products. ♡ This can be done by heating the crude oil and collecting the fractions that boil over different ranges of temperatures. ♡ This is different to distillation which is just heating and condensing liquids to purify them
what are the names of 2 gases produced in fractional distillation?
♡ Oxygen ♡ Nitrogen
Give the order of Fractions and their temperature in fractional distillation starting from the bottom:
Vaporised crude oil goes in DIESEL (300°) C15C19 then KEROSENE (200°) C11C15 then NAPHTHA (110°) C7C14 then GASOLINE (40°) C4C12 then at the top FUEL GASES (25°) C1C4 but then at the bottom RESIDUE (350°) C20
Give the jobs of DIESEL KEROSENE NAPHTHA GASOLINE FUEL GASES AND RESIDUE
DIESEL (GAS OIL) fuel for diesel engines ♡ KEROSENE jet fuel ♡ NAPHTHA petrochemicals ♡ GASOLINE petrol for cars ♡ FUEL GASES Calor gas, LPG RESIDUE distilled further at lower pressures to give FUEL OIL LUBRICATING OIL WAXES and BITUMEN
State the term that can be used to describe alkanes which have entirely dingle bonds within their structure
Saturated (be able to define saturated Hydrocarbon)
Name and describe the process used to separate the components of crude oil
♤ Fractional distillation ♡ Crude oil is vaporised through heating ♡ hotter at the bottom cooler at the top (temperature gradient) ♡ different fractions have different boiling points ♡ longer chains have higher boiling points that shorter chains
Explain why hydrocarbons undergo industrial cracking. What must happen to the hydrocarbons during this process?
♡ break C-C bonds ♡ we do this so that short chain hydrocarbons (which are in more demand) can be produced
Describe the two methods of cracking used industrially
Catalytic: Low pressure 500°C zeolite catalyst (produces branched cyclic and aromatic alkanes ) ♡ Thermal: 450-750°C pressure of 70 atmospheres and this produces lots of alkenes
Explain why cracking is used in industry
Shorter chain hydrocarbons are in more demand and therfore cracking is used to produce more of these shorter chains
Give equations to show what happens during incomplete combustion of ethane
C2H6 + O2 —> CO + C + H20 C2H6 + O2 —> CO + C + 3H20 C2H6 + 2O2 —> CO + C + 3H20
Sate what products are formed when hydrocarboms undergo incomplete combustion?
♡ Water ♡ CO ♡ Nitrogen ♡ Sulfur ♡ Carbon
Complete the equation to show the complete combustion of butane
C4H10 + 6.5 02 –> 4CO2 + 5H2O
Explain why alkanes are used as fuels
They are saturated Hydrocarbons. They are used as fuels because they can be cracked to produce useful substances such as petrol.
State the term that can be used to describe alkanes which have entirely single bonds within their structure
Saturated
Name and describe the process used to separate the components of crude oil
❣️ Fractional Distillation
🥚Crude oil is vaporised through heating
🥚hotter at the bottom, cooler at the top (temperature gradient)
🥚different fractions have different boiling points
🥚longer chains have higher boiling points than shorter chains
Explain why hydrocarbons undergo industrial cracking. What must happen to the hydrocarbons during this process
💕break C-C bonds
💕we do this so that short chain hydrocarbons (which are in more demand) can be produced
Describe the two different methods of cracking used industrially
🌸 Catalytic : Low pressure, 500•C, zeolite catalyst (produces branched, cyclic and aromatic alkanes)
🌸Thermal: 450-750•C, pressure of 70 atmosphere and this produces lots of alkenes
Explain why cracking is used in industry
Shorter chain hydrocarbons are in more demand and therefore cracking is used to produce more of the shorter chains
Explain why alkanes are used as fuels
Because they can be combusted to produce substances such as petrol
State what products are formed when hydrocarbons undergo incomplete combustion
❣️Water
❣️Carbon monoxide
❣️Carbon
Give equations to show what happens during incomplete combustion of ethane
🔥 C2H6 + 2.5 O2 –> 2CO + 3H2O
🔥 C2H6 +1.5 O2 –> 2CO+ 3H2O
Cars are fitted with catalytic converters to remove some pollutants.Name the two metals that act as a catalyst in the catalytic converter
👑 platinum
👑 rhodium
👑 palladium
Some of the hydrocarbon fuels can contribute to acid rain. Explain why
🍂 Burning hydrocarbon fuels produces carbon dioxide.
🍂Incomplete combustion creates poisonous carbon monoxide.
🍂Some of the products from burning fuels dissolve in rain water to form acid rain.
🍂Many fossil fuels contain sulfur impurities and when those fuels are burned the sulfur is oxidized to form sulfur dioxide
Describe how SO2 is removed from flue gases
They can be removed after the combustion of the fuel. The SO2 is treated with powdered limestone to form calcium sulfate. This can be used to make plaster board, turning a harmful product into a useful one.
