C9 - Crude oil and fuels

Question 1

What is crude oil?

Answer 1

a finite resource that is found in rocks, and is a mixture of a large number of hydrocarbon compounds (mainly alkanes)

Question 2

How is crude oil made?

Answer 2

it is made from the remains of ancient biomass from marine organisms (mainly plankton) buried under mud over hundreds of millions of years

Question 3

What is a technical name for the alkanes? What is its definition?

Answer 3

-a homologous series
-a sequence of organic compounds with the same functional group and similar chemical properties

Question 4

What are the first 4 alkanes?

Answer 4

-methane
-ethane
-propane
-butane

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Question 5

If asked for a general formula for a homologous series, how should you answer it?

Answer 5

write what is shown below, don’t just put 2n-2

this general formula was for cycloalkenes

Question 6

How is crude oil turned into a useful product?

Answer 6

-by fractional distillation, where it is separated into different fractions containing molecules of similar lengths

-each fraction is processed to produce fuels and feedstock for the petrochemical industry

Question 7

State some examples of materials produced by fractional distillation:

Answer 7

solvents, lubricants, polymers, detergents

Question 8

State some examples of fuels produced by fractional distillation:

Answer 8

petrol, diesel, kerosene, heavy fuel oil, LPGs

LPG is liquified petroleum gas, not light

Question 9

Describe the full process of fractional distillation of crude oils:

Answer 9

-crude oil is vaporised (turned into a gas) by heating
-hydrocarbon gases enter fractionating column and rise
-cools down as they get higher
-when the hydrocarbon cools enough to reach their condensing/boiling point, they condense into a liquid
-liquid is collected and separated

Question 10

Why might nonane condense lower in a fractionating column compared to smaller alkanes?

Answer 10

-nonane has a higher boiling point
-therefore it will condense at a higher temperature, which is found lower in the fractionating column

Question 11

Describe how 3 factors change with increasing hydrocarbon molecule size:

Answer 11

-boiling point increases
-viscosity (thickness) increases
-flammability decreases

Question 12

Describe the process of complete combustion with a hydrocarbon fuel:

Answer 12

-exothermic reaction involving the oxidation of the carbon and hydrogen from the hydrocarbon fuel
-complete combustion produces CO₂ and H₂O

Incomplete combustion often forms CO gas or C particulates

Question 13

How can longer hydrocarbon chains be broken down into smaller ones? Describe this process:

Answer 13

-cracking, 2 methods can be used:

catalytic - high temperature to vaporise HCs and pass over hot catalyst
steam - high temperature to vaporise HCs and mix with steam

Question 14

What are the products of cracking? Compare their reactive properties:

Answer 14

-alkanes and alkenes
-alkenes are more reactive

Question 15

How can you test for the presence of an alkene?

Answer 15

alkenes react with bromine water, turns orange to colourless

Question 16

Give some uses of alkenes:

Answer 16

-polymers
-starting materials for the production of many other chemicals

Question 17

Why is cracking necessary?

Answer 17

-there is a higher demand for smaller hydrocarbons because they’re usually better fuels as they are easy to ignite
-however most of the fractions have long chains
-cracking takes the longer chains and breaks them down into smaller, more useful chains

They are easy to ignite since they have a higher volatility, making them very flammable

Question 18

What is the difference between a molecule being saturated and unsaturated? Give an example:

Answer 18

saturated - only single bonds, alkanes

unsaturated - has one or more double/triple bonds, alkenes

Question 19

Why are sulfur impurities removed from petrol before it is burnt in car engines?

Answer 19

-the sulfur might react with oxygen to form sulfur dioxide (SO₂)
-can dissolve in rainwater to form acid rain

Question 20

Why is soot sometimes produced when burning fossil fuels?

Answer 20

-incomplete combustion occurs
-due to insufficient oxygen

Question 21

How would reducing the amount of sulfur in fossil fuels reduce the erosion of limestone?

Answer 21

-less sulfur would react with oxygen in combustion to form sulfur dioxide
-less sulfur dioxide emitted by the car
-less dissolves in precipitation to form acid rain
-limestone reacts less with acid rain

Question 22

Why are oxides of nitrogen formed in car engines?

Answer 22

-car engines operate at very high temperatures
-this means nitrogen from the air can react with oxygen from the air to form oxides of nitrogen