C9- Crude Oil And Fuels Flashcards
What is Crude oil?
A finite resource found in rocks. It was formed over millions of years from the remains of tiny, ancient sea animals and plants ( mainly plankton).
What is crude oil’s appearance?
It is a dark, smelly liquid. It is a mixture of different carbon compounds.
What is a mixture?
A mixture contains two or more elements or compounds that are not chemically combined together.
What needs to be done to crude oil in order to make it useful?
It must be separated into different substances with similar boiling points. These are known as fractions.
Name the first four Alkanes
CH4
C2H6
C3H8
C4H10
What is the formula for propane?
C3H8
What is the formula for Ethane?
C2H6
What is the general formula for Alkanes?
Cn H(2n+2)
Why can Alkanes be described as Saturated Hydrocarbons?
All the Carbon-Carbon bonds are single covalent bonds. This means that they contain as many hydrogen atoms as possible in each molecule.
Which chain-length hydrocarbons tend to be most useful?
The short-chain molecules
Key features of Short Chain Hydrocarbons
Lower boiling point
Higher volatility
Low viscocity (very runny)
Higher flammability
Key features of long chain hyrocarbons
Higher boling point
Lower volatility
High viscocity
Lower flammability
What is flammability?
How easily sonething burns
What is viscocity?
How easily something flows
What is volatility?
The tendency for something to turn into a gas
What is boiling point?
The temperature at which the liquid boils or the gas condenses
What is fractional distillation?
Where crudeoil is separated into hydrocarbons with similar boiling points called fractions
What do hydrocarbons have to have to be in the same fraction?
Molecules with similar numbers of carbon atoms
Fractional distillation Explained
Crude oil is heated and fed in near the bottom of a tall tower (called a fractionating column) as hot vapour. The column is kept very hot at the bottom and much cooler at the top, so the temperature decreases going up the column. The gases move up the column and the hydrocarbons condense when they reach the temperature of their boiling points. The different fractions are collected as liquids at different levels. The fractions are collected from the column in a continuous process.
What is the name of the apparatus where fractional distillation takes place?
Fractionating column
What is at the top of the fractionating column (lowest temp of 50 degrees)
Refinery/petroleum gas
What is at the bottom of the fractionating column (highest temp of 350 degrees)
Residue
Fractionating column in order (starting from the bottom and highest temp)
Residue
Diesel oil/ gas oil (diesel engines and as boiler fuel)
Kerosene ( aircraft fuel )
Gasoline/petrol ( fuel in car engines)
Refinery / petroleum gas ( used as fuel)
What are the products of the complete combustion of a hydrocarbon?
Carbon dioxide and water
What colour does white anhydrous copper sulfate turn on contact with water ( testing for products of complete combustion)?
Blue
What is the toxic product formed in incomplete combustion?
Carbon monoxide- binds to red blood cells instead of oxygen
Why crack hyrocarbons?
Because some heavier fractions are not in high demand and smaller ones are more useful and are in higher demand.
What is the name of the process where larger hydrocarbon molecules are broken down into smaller more useful ones?
Cracking
Which two ways are used for cracking hydrocarbons?
The process takes place in steel vessels called crackers. The heavy fractions are heated to vaporise the hydrocarbons. The vapour is then either:
. Passed over a hot catalyst, or
. Mixed with steam and heated to a very high temperature
What type of reaction takes place during cracking?
Thermal decomposition reactions take place as the large molecules split apart to form smaller ones
What suffix/ending do unsaturated hydrocarbons have?
-ene
What is the difference between alkanes and alkenes ?
Alkene molecules have two fewer hydrogen atoms than alkanes with the same number of carbon atoms.
Test for an unsaturated hydrocarbon
It turns orange bromine water colourless
What is Combustion?
Fuels react with oxygen to release energy
Conditions for complete combustion
Plentiful supply of air (oxygen)
Conditions for incomplete combustion
Supply of air is limited (lack of oxygen)
Unwanted products of incomplete combustion
Carbon monoxide, unburnt hydrocarbon and soot
Product of Combustion of Sulfur
Sulfur dioxide (can cause acid rain)
Products of reaction of Nitrogen and oxygen (at high temp and often in engines)
Nitrogen oxides (cause acid rain)
How to reduce problem of acid rain
Sulfur dioxide- Remove by flue gas desulfurisation
Nitrogen oxides- Catalytic converters in cars
