Fractional Distillation Flashcards
Alkanes are saturated Hydrocarbons, what does that mean ?
Hydrocarbons are molecules that only contains C + H. Alkanes are saturated which means it only has a C-C single bond.
What is the difference between Shorter and longer chain Alkanes?
The longest hydrocarbons (heavier fractions):
- condense at high boiling points = less flammable
-< vdw forces = more energy to separate
- leave the column as bitumen
- Negative temperature gradient on the column
Shorter hydrocarbon molecules:
- weaker intermolecular forces
- Top of column has a negative temperature gradient (lower b.p)
- highly volatile = flammable
-> vdw forces = less energy to separate
Explain Fractional Distillation (6 Marks)
- Fractional distillation is the process of separating the different hydrocarbon compounds within crude oil.
- First the crude oil is vaporised at around 350C
- and fed into a fractionating column which has a temperature gradient, meaning that Its hotter at the bottom and cooler at the top
-Long chain hydrocarbons with higher boiling points will condense at lower fractions in the column - whilst shorter chain hydrocarbons with lower boiling points will condense at higher fractions in the column.
- These fractions now hold liquid hydrocarbons which will be collected through pipes. Some hydrocarbons with very low boiling points such as natural gases will escape out of the top of the column whilst some hydrocarbons with very high boiling points do not vaporise such as bitumen, which leaves through the bottom of the column.
What type of process is Fractional Distillation
- Fractional distillation is a physical process, not chemical
- no covalent bonds are broken
- The intermolecular forces between molecules are broken as the crude oil is heated
What is fractional Distillation a Mixture of ?
It is a mixture of mostly alkanes, unbranched and branched chain
The mixture is separated into fractions, based on boiling points.
Most fractions contain mainly alkanes, which are compounds of carbon and hydrogen with only single bonds between them
what does each Fraction Consist of?
Each fraction consists of groups of hydrocarbons of similar chain lengths
Do Hydrocarbons of similar chain length have similar boiling points?
YES!
What determines which fraction it will be separated into?
The size and length of each hydrocarbon molecule.
What does the size of each molecule is directly related to?
How many carbon and hydrogen atoms the molecule contains.
Procedure of Fractional Distillation?
1) Turn on h20 , fill condenser
2) Heat flask and Bunsen burner
3) H20 and ethanol turn to vapour
4) Fractionating column has a temp gradient, ethanol and water separate due to different boiling points
5) Only ethanol goes into condenser.
6) Condenser used to cool vapour and condense ethanol into liquid.
What is crude oil and why is it important to separate it into fractions?
Crude oil is a mixture of hydrocarbons that is extracted from the earth. It is important to separate it into fractions because each fraction has different properties and uses, and can be further processed into useful products like gasoline, diesel fuel, and lubricating oil.
How is crude oil separated into fractions?
Fractional distillation, which involves heating the oil to vaporise it and then cooling the vapour to condense it into different fractions based on their boiling points.
What are the different fractions that crude oil is separated into?
Crude oil is typically separated into fractions including gases, naphtha, kerosene, diesel fuel, lubricating oil, and residual fuel oil, ect.
How are the different fractions of crude oil used?
to create end products, with gases used for heating and cooking, naphtha and kerosene used as solvents and feedstock for the production of chemicals, and diesel fuel and lubricating oil used for transportation and machinery.
What is the importance of fractional distillation in the petroleum industry?
Fractional distillation is a crucial process in the petroleum industry as it enables the production of different products from crude oil that have specific uses and properties, allowing for efficient and effective use of this valuable resource.
Name the two important conditions for fractional distillation
The liquids should be miscible With one another. The difference in boiling point between the two liquids must be less than 25-degree Celsius.
What is the Purpose of Fractional Distillation?
Fractional distillation is very useful when separating more than two types of liquids from a homogeneous mixture. This method is particularly useful in separating liquids that have less than 25°C difference in boiling points.
State the meaning of both the words saturated and hydrocarbon as applied to the term saturated hydrocarbon.
Name the homologous series to which C8H18 belongs.
-Single bonds only /no double or multiple bonds;
-Contains carbon and hydrogen only;
C and H only not C and H molecules
-Alkanes
Outline the essential features of the fractional distillation of crude oil that enable the crude oil to be separated into fractions. (4)
(1) Fractions or hydrocarbons or compounds have different boiling points/ separation depends on bp;
(2) bp depends on size/ Mr/ chain length;
(3) Temp gradient in tower or column / cooler at top of column or vice versa;
(4) Higher bp / larger or heavier molecules at bottom (of column) or vice versa;
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.
Write an equation to show how one molecule of C14H30 is cracked to form one molecule of C8H18 and one molecule of another hydrocarbon.
Explain why oil companies need to crack ‘suitable heavy fractions’.
-Large molecules or compounds or long chain hydrocarbons (broken) into smaller molecules or compounds or smaller chain hydrocarbons;
Zeolite or aluminosilicate (catalyst);
-C14H30 → C8H18 + C6H12;
-Smaller chain molecules are in more demand or have higher value or vice versa;
The molecular formula C8H18 represents several structural isomers.
State what is meant by the term structural isomers.
Name the following structural isomer of C8H18
- (compounds with) same molecular formula / same no and type of atoms;
- Not atoms/elements with same molecular formula.
And different structure/ structural formula; - 2,2,4-trimethylpentane;
Crude oil is separated into fractions by fractional distillation. Outline how
different fractions are obtained by this process.
- Crude oil is heated to vaporise it
- Vapour passed into fractionating columns
- Top of column has a negative temperature gradient
- Fractions are condensed at different temperatures
Give the two main types of product obtained by catalytic cracking
- Identify shortfall in supply - e.g. petrol / small molecules (1)
- Higher value products
Name a catalyst used in catalytic cracking. State the type of mechanism involved and outline the industrial conditions used in the process.
Motor fuels Aromatic hydrocarbons Branched alkanes / hydrocarbons Cycloalkanes
What is the order of the products in the different fractionating columns from the bottom (high b.p).
Order =
- Residue (Bitumen for roads and roofs)
- Mineral oil (lubricating oil),
- Gas oil (diesel),
- Kerosene (paraffin - aircraft fuel),
- Naphtha (making chemicals),
- Petrol (gasoline),
- Refinery gasses (non-condensable gas e.g H, C2H6, CH4)
Sulphur Dioxide
Sulphur (containing impurities) burn to form or forms SO2 or oxides of sulphur (if oxide identified, must be correct) (1) OR equation: e.g. S + O2 → SO2 or H2S + 1½O2 → SO2 + H2O
Leading to acid rain (must have specified oxides of S or burning) or toxic product or respiratory problems
as it is poisonous (1)
Nitric Oxide
NO formed by reaction between N2 and O2 from the air (1) OR N2 +O2 → 2NO High combustion temperature or spark in engine (1) provides EA or sufficient heat / energy to break N
N (1)
What does the molecular formula gives?
the molecular formula gives the actual number of atoms of each element
What is fractional distillation and how is it different from distillation? (Alkanes and crude oil)?
Fractional distillation separates a mixture into several components with different ranges of boiling points whereas distillation simply separates all the volatile components of a mixture from the non-volatile ones
What is cracking
The smaller hydrocarbon fractions (such as gasoline fractions) are in high demand compared to the larger ones
Therefore, some of the excess heavier fractions are broken down into smaller, more useful compounds
These more useful compounds include alkanes and alkenes of lower relative formula mass (Mr)
This process is called cracking
cracking
The large hydrocarbon molecules are fed into a steel chamber and heated to a high temperature and then passed over an aluminium oxide (Al2O3) catalyst
The chamber does not contain any oxygen to prevent combustion of the hydrocarbon to water and carbon dioxide
When a large hydrocarbon is cracked, a smaller alkane and alkene molecules are formed
Eg. octane and ethene from decane The low-molecular mass alkanes formed make good fuels and are in high demand
The low-molecular mass alkenes are more reactive than alkanes due to their double bond
This makes them useful for the chemical industry as the starting compounds (feedstock) for making new products
Eg. they are used as monomers in polymerisation reactions
Shorter Alkane (CnH2n+2) ?
- more useful = make more money
Use for Alkenes (CnH2n) ?
- Bromine water test = from orange to colourless
- to make plastics via polymerisation reaction
What is Catalytic Cracking ?
- 450C w/catalyst
- the catalyst = zeolite = SiO2 & Al2O3
- honeycomb structure = to increase S.A.
- form aromatic compounds (contain benzene ring) & fuels
- /\/\/\/\ = zig zag formation is a Aliphatic
Thermal Cracking ?
- high temp 1000K
+ - high pressure
= form small alkanes and alkenes
Haloalkanes have the same general formula + the halogen, e.g C = 1 therefore C1H4CL? Do they have the same general formula?
- they have the same general formula, but not that it is the same as for the alkanes!
- remove a hydrogen and replace it with the halogen
- and that only really works simply for the haloalkanes where there is just the one halogen bonded.
What do Cracking Equation always produce?
- a mixture of alkanes and alkene
Cracking Equation: A hydrocarbon was cracked into pentane, 2 molecules. of Ethene & an Alkene with 3 C atoms, write an equation for this
C12H26 -> 2C2H4 + C3H6 + C5H12
How to work out Empirical formula?
S-MADR
S - symbol
M - mass given
A - Ar value
D - divide (when you find the answers to this then divide it again by the smallest number)
R- ratio
How to work out Molecular formula
- do given Mr divided by given empirical formula
- then times the small numbers by the answer
What is free radical substitution?
- ALKANES can be made into HALOGENOALKANES, through the process of free radial substitution
What is a radical
- A reactive species with unpaired e-
what is CFCs?
- chlorofluorocarbon
e.g CHClF3
CCl2F2
What is CFCs used for (CFCs breaking down to produce ozone) = application in real world
- solvents and repellants in areosole cans
- Chlorine radical is produced as UV light breaks bonds and this attacks the ozone so it forms:
- Cl. + O3 -> 02+ ClO
- ClO. + 03 -> 2O2+Cl.
- ozone in atmosphjere filter out UV radiaction = protection
What is an alkane?
A saturated hydrocarbon containing C-H bonds only
What is the general formula of an alkane?
CnH2n+2
Which reactions will alkanes undergo?
Combustion and reaction with halogens
How reactive are alkanes?
very unreactive
Are they soluble in water (non polar)? Why?
- Insoluble because hydrogen bonds in water are stronger than alkanes’ van der Waals forces of attraction
- Only van der Waals forces of attraction - bonds are non-polar
- Non-polar because carbon and hydrogen have similar electronegativities
Name Alkanes
CH4 - methane
/ CH3 CH3 - ethane
/\ CH3 CH2 CH3 - propane
/\/ - butane
- pentane
- hexane
Chain isomerism
e.g butane is /\ = butane but also /|\ = methylpropane (109.5 degrees)
Cycloalkanes
= rings
boiling point is low and high
- as molecule gets longer b.p increases
- larger alkanes = liquid
- v large = solids
- branching = lower b.p than unbranched
solubility
- insoluble in water
- water is polar solvent therefore non-polar substances dont dissolve well
Why is Alkanes very unreactive?
- bec C- C bonds are strong
- flammable = fuels
- Lubricant
- Make other organic molecules
what type of flames do shorter alkanes have
- Clean Flame
what type of flames do longer alkanes have
- Sootier flame
what is a fuel
something that releases heat energy is at burns
Combustion Equations
- CH4(g) + O2 -> CO2 (g) + H2O (l)
Incomplete
- carbon monoxide
- soot = No CO2 or O
- Not enough O to make the flame burn cleanly e.g. longer chain alkanes
What are Functional groups
- atoms or groups of atoms in a compound that determine its characteristic reactions.
