Chemistry 4.5 Flashcards
What is crude oil?
A mixture of hydrocarbons
What is a hydrocarbon?
A compound that only contains hydrogen and carbon
Why is crude oil separated into fractions?
Most of the hydrocarbons are useful but they have different purposes. They’re separated into fractions which contain similarly used molecules.
Use of refinery gases
Fuel for homecooking
Use of gasoline
Fuel for cars
Use of kerosene
Fuel for aircrafts
Use of diesel
Fuel for lorries, buses (trains)
Use of fuel oil
Fuel for ships
Use of bitumen
Making roads
Order of fractions in fractional distillation (start from top)
Refinery gases, gasoline, kerosene, diesel, fuel oil, bitumen
Trend in colour for the fractions
Gets darker as you go down (refinery gases are the lightest)
Trend in boiling point for the fractions
Boiling point increases as you go down the group (refinery gases have lowest boiling point, hence why they are gases)
Trend in viscosity for the fractions
Viscosity increases as you go down the group (bitumen is the most viscous)
What happens as RFM of fractions increases?
Boiling point increases, viscosity increases, colour gets darker
Describe how the industrial process of fractional distillation separates crude oil into fractions
- Heated crude oil vapours enter the column.
- Vapours rise until they reach their boiling point, when they condense.
- Different vapours condense at different heights due to their different boiling points.
- Similar vapours condense together as a fraction.
What is used to separate crude oil into fractions?
Fractional distillation
What are fractions?
Mixtures containing hydrocarbons that boil in a particular temperature range
How does the temperature differ in the fractionating column
Hotter at the bottom, colder at the top (this links to the fractions boiling points)
Mnemonic for remembering order of fractions
Random Gases Kill During Furious Battles
What are alkanes?
Saturated hydrocarbons that fit the general formula Cn H2n+2
Formula of methane
CH4
Formula of ethane
C2H6
Formula of propane
C3H8
Formula of butane
C4H10
Formula of pentane
C5H12
Formula of hexane
C6H14
Alkanes are homologous, what does that mean?
They have similar chemical reactions, trends in physical properties and they all have the same general formula.
General formula for alkanes
Cn H2n+2
Equation for the complete combustion of a hydrocarbon
Hydrocarbon + oxygen –> carbon dioxide + water
Products of incomplete combustion of alkanes
Carbon monoxide and soot
Describe the negative effects of the products of incomplete combustion of alkanes
Carbon monoxide - lowers the oxygen-carrying capacity of the blood
Soot - causes lung disease
What are the main pollutants formed from the combustion of hydrocarbons?
Carbon dioxide
Nitrogen oxides
Sulphur dioxides
Carbon monoxide
How is nitrogen oxide formed by the (complete) combustion of alkanes and what are the problems?
In car engines, the high temperatures allow nitrogen and oxygen from the air to react, forming nitrous oxides. When nitrous oxides dissolve in rainwater, they form acid rain.
How is sulphur dioxide formed by the (complete) combustion of alkanes and what are the problems?
When sulphur impurities in the hydrocarbon fuel combust, sulphur dioxide is formed. When dissolved in rainwater, it forms acid rain.
How is carbon dioxide formed by the (complete) combustion of alkanes and what are the problems?
Formed directly from the combustion of alkane fuel. A greenhouse gas that traps heat in the atmosphere, leading to climate change.
Are alkanes saturated or unsaturated and why?
Saturated, there are no double bonds
What is a functional group?
Group of atoms in a molecule with distinctive chemical properties
Are alkenes saturated or unsaturated and why?
Unsaturated, they contain a double carbon-carbon bond
What is the general formula of alkenes?
Cn H2n
Define isomers
Same molecular formula but different structural formula
What would you call an isomer of butene that has a double bond in the middle/that starts in position 2
But-2-ene
What is the functional group of alkenes?
Carbon-carbon double bond
Are alkenes more or less reactive than alkanes and why?
They can make more bonds with other atoms by opening up the double carbon-carbon bond
What type of reaction is the reaction between bromine and alkenes?
Addition reaction
What is formed when alkenes and bromine react?
dibromoalkanes are formed (double carbon bond is broken)
What happens when bromine water is added to an alkane
It remains orange coloured
What happens when bromine water is added to an alkene?
The solution decolourises as it no longer contains free bromine (bromine atoms add across the double carbon bond)
What happens when a halogen and an alkene react?
Same as reaction with bromine, halogen atoms always add to the carbon atoms across the double carbon bond
How are addition polymers formed?
From monomers containing double carbon bonds. Double carbon bond of the monomer breaks and the monomer forms a single covalent bond with an adjacent monomer.
Why are addition polymers hard to dispose of?
They are unreactive and chemically inert so they don’t biodegrade. This is because of strong carbon bonds
What is the problem with incinerating polymers?
They releases a lot of energy when burnt as well as producing carbon dioxide (greenhouse gas contributing to climate change)
Polymers containing chlorine release toxic hydrogen chloride gas when burnt.
If incinerated with incomplete combustion, carbon monoxide will be produced
What conditions are required for the reaction of alkanes and bromine?
UV light
What type of reaction is alkane and bromine?
Substitution
What catalysts are used for cracking?
Alumina/silica
Reasons for cracking
Higher demand for shorter-chain hydrocarbons.
Over supply of longer-chain hydrocarbons.
Alkenes used to make polymers
What happens during cracking?
Long alkane is broken down into a shorter alkane and alkene
Conditions needed for cracking
650oC and alumina/silica catalyst
