Topic 8- Fuels (paper 2)

Question 1

How can crude oil be separated?

Answer 1

Fractional distillation

Question 2

How is crude oil separated?

Answer 2

1. Oil is pumped into fractionating column
2. Temperature gradient runnning through the fractional column (hottest at base, coolest at top)
3. The smaller molecules evapourate from the oil and at the bottom of the column the liquid that remains (bitumen) is drained off
4. The gas rises up the column and gradually cool
5. Different compounds in the mixture have different boiling points and so they condense at different temperatures and therefore different levels in the fractionating column.

Question 3

Name what is produced in the fractionating column from top to bottom and their uses

Answer 3

1. gas- domestic heating and cookers
2. petrol- cars
3. kerosene- jet fuel
4. diesel oil- cars and trains
5. fuel oil- for ships and large powerstations
6. bitumen -surface roads / rooves

Question 4

Hydrocarbons which share similar chemical properties can be grouped together in the same…

Answer 4

Homologous series

Question 5

What is the trend in boiling points as hydorcarbons get bigger?

Answer 5

Increase in boiling point as the chains are longer

Question 6

How do the intermolecular forces differ between a small carbon chain and a larger carbon chain?

Answer 6

The intermolecular forces are stronger between longer chain molecules as there are more atoms to be attracted to eachother through these intermolecular forces, hence why longer chains have higher melting points

Question 7

What is viscocity?

Answer 7

How easily a substance flows

Question 8

What is the link between viscocity and hydrocarbons?

Answer 8

Longer chain carbons have more intermolecular forces and therefore higher viscocities

Question 9

What is the word equation for complete combustion of a hydrocarbon?

Answer 9

hydrocarbon + oxygen → carbon dioxide + water

Question 10

When will incomplete combustion occur?

Answer 10

When combusiton occurs with insufficient oxygen present

Question 11

What are the two forms of incomplete combustion? (word equation)

Answer 11

hydrocarbon + oxygen → carbondioxide + carbon monoxide + water
hydrocarbon + oxygen → carbon + carbon monoxide + water

Question 12

what other toxic chemicals can be released in the burning of fossil fuels?

Answer 12

various nitrogen oxides, but most importantly sulphur dioxide which causes acid rain

Question 13

what are hydrocarbons?

Answer 13

compounds containing only hydrogen and carbon

Question 14

what is crude oil?

Answer 14

Crude oil is a finite resource containing a mixture of different long chains of hydrocarbon molecules

Question 15

what is the trend in ease of ignition between different hydrocarbons in the fractionating column

Answer 15

The higher a substance is in the fractionating column, the more easily it is ignited (therefore the gas is the most easily ignited while the bitumen is the most difficult to light)

Question 16

what is the trend in viscocity between different hydrocarbons in the fractionating column

Answer 16

going down the fractionating column, viscocity increases (bitumen has the highest viscocity)

Question 17

what is the difference between neighbouring compounds in the same homologous series (in terms of atoms?)

Answer 17

CH₂

Question 18

what are the unwanted products of incomplete combustion?

Answer 18

carbon monoxide and soot

Question 19

why does incomplete combustion produce carbon and carbon monoxide?

Answer 19

due to the lack of oxygen, oxygen particles are lost from CO₂ compounds to form CO and C

Question 20

how is carbon monoxide a toxic gas?

Answer 20

the CO binds to the haemoglobin in red blood cells meaning that the oxygen inside the body cannot bind to the red blood cells and be carried round the body resulting in the body’s organs becoming deoxygentaed- potentially leading to death

Question 21

why, where and when are nitrogen oxides produced

Answer 21

In the engines of cars, when lots of energy is released as heat, oxygen and nitrogen molecules from in the air react to form nitrogen oxides that can contribute to acid rain and cause photochemical smog.

Question 22

advantages of using hydrogen as an alternative to petrol

Answer 22

• only waste product is water
• no harmful polutants like carbon monoxide, soot or nitrus oxide

Question 23

what are the disadvantages of using hydrogen over petrol?

Answer 23

• more expensive
• highly flammable
• hard to store

Question 24

What is cracking?

Answer 24

When a longer alkane molecule is broken down to produce an alkene and a shorter alkane molecule

Question 25

how does cracking work?

Answer 25

• it’s a thermal decomposition reaction
• vapourised hydrocarbons are passed over a powdered catalyst
• a lot of energy is required so cracking is carried out between 400-700°C
• a pressure of 70 atm and an aluminium oxide catalyst is also used