Cracking Flashcards

1
Q

cracking

A

a process carried out on fractions in oil refineries after fractional distillation

larger alkanes are broken down into smaller, more useful alkanes and alkenes

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2
Q

Describe the process of cracking

A
  • crude oil is heated and evaporated
  • vapour passes over a catalyst containing aluminium oxide
  • heated to about 650C to speed up the reaction
  • molecules are broken down
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3
Q

need for cracking

A

-long, saturated molecules are not very useful

  • short molecules are in higher demand than their production
  • long molecules are in lower demand than production
  • short molecules are in higher demand than long molecules
  • shorter alkanes are useful as fuels
  • alkenes are used to make polymers
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4
Q

products of cracking

A

alkanes - useful as fuels
(shorter chains)

alkenes - used to make polymers
(contain a double bond between at least two carbon atoms)

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5
Q

alkenes

A

contain a double bond between at least 2 carbon atoms

used to make polymers - polyester, nylon

unsaturated (with at least 1 double bond)

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6
Q

(un)saturated molecule

A

a saturated molecule contains only single bonds

an unsaturated molecule has at least one double bond

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7
Q

Give an example of what C8H18 could be broken down into

A

C8H18 -> C6H14 + C2H4

etc

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8
Q

How can you tell if a molecule is an alkane or an alkene?

A

due to the arrangement of atoms:

an alkane always has an amount of hydrogen atoms equal to double the carbon atoms + 2

(e.g. C6H14)

an alkene has double the amount of hydrogen atoms compared to carbon atoms

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9
Q

Describe the setup for cracking paraffin in the lab

A
  • paraffin is absorbed by mineral wool and placed in the end of a test tube
  • broken porous pot is placed in the tube as a catalyst
  • a bung and delivery tube cause the product (ethene gas) to build up in an upturned test tube
  • the test tube is placed in a container of water
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10
Q

Describe the process for cracking liquid paraffin in the lab

A
  • the porous pot catalyst is heated strongly
  • liquid paraffin is heated and evaporated
  • paraffin vapour passes over the hot porous pot and the hydrocarbon molecules break down
  • one of the products is ethene, which is a gas and collects in the other tube
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11
Q

List all the equipment needed for cracking liquid paraffin

A
  • liquid paraffin
  • mineral wool
  • broken porous pot
  • test tubes
  • bung
  • delivery tube
  • container with water

-method of heating

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12
Q

Use the information below to explain how cracking helps to balance supply with demand.

Supply/demand of some of the fractions obtained from crude oil as a percentage of all the fractions:

Petrol:
Supply = 10%
Demand = 30%

Bitumen and fuel oil:
Supply = 40%
Demand = 20%

A

some larger alkanes (bitumen) are in greater supply than their demand

cracking converts these alkanes into smaller hydrocarbons (petrol) which are in greater demand than can be supplied by fractional distillation alone

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13
Q

a) Give the formula of the substance needed to balance this cracking reaction equation:

C10H22 -> C8H18 + ?

b) State a use for the hydrocarbon in a) other than as a fuel

A

a) C2H4

b) can be used to make polymers

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