Organic (3.3)

Question 1

Why is cracking used?

Answer 1

-Low demand but high supply of long-chain hydrocarbons
-High demand but low supply of shorter-chain (especially naptha fraction)
Alkenes produced are much more reactive than naturally occurring alkanes, so better used as fuels

Question 2

What is cracking?

Answer 2

Splitting up of longer-chain hydrocarbons to produce shorter chain hydrocarbons

Question 3

What conditions are required for thermal cracking?

Answer 3

• 700-1200K

- 7000kPa

Question 4

What are the products of thermal cracking?

Answer 4

• Alkanes & Alkenes (1:1)

- Formed through intermediate, highly reactive free radicals

Question 5

What conditions are required for catalytic cracking?

Answer 5

• 720K
• Slight pressure
• Zeolite catalyst (honeycomb structure, aluminium oxide & silicon dioxide)

Question 6

What are the products of catalytic cracking?

How are they separated?

Answer 6

• Branched alkanes
• Cycloalkanes
• Aromatic compounds

-Separated by fractional distillation

Question 7

Describe features of fractional distillation

Answer 7

• Continuous process
• Large scale
• Multiple collection points
• Produces fractions (mixtures of similar bpts)
• Used to separate complex mixtures with close bpts)

Question 8

Describe the features of simple distillation

Answer 8

• Batch process
• Small scale
• Single collection point
• Produces pure substances (single bpt)
• Used to separate simple mixtures with widely different bpts

Question 9

What is isomerism?

Answer 9

Molecules with the same molecular formula, whose atoms are arranged differently

Question 10

What is structural isomerism?

Answer 10

Molecules with the same molecular formula, with differing structural formulae

Question 11

What is position isomerism?

Answer 11

(STRUCTURAL)

-The functional groups are the same but attached to the chain at differing points

Question 12

What is functional group isomerism?

Answer 12

(STRUCTURAL)

-Same molecular formula but different functional groups

Question 13

What is chain isomerism?

Answer 13

(STRUCTURAL)

• Same molecular formula but the chain is arranged differently
• (e.g. branching etc)

Question 14

What is stereoisomerism?

Answer 14

Molecules have the same structural formula, but are arranged differently in space

Question 15

What is geometric isomerism?

Answer 15

(STEREO)

• E-Z isomerism refers to the orientation of the largest molecules around a double bond
• E=different side
• Z=same side

Question 16

How does geometric isomerism arise?

Answer 16

It arises due to restricted rotation about a double bond

Question 17

What is optical isomerism?

Answer 17

(STEREO)

• Occurs when four different substituents are attached to one carbon atom (chiral carbon)
• Essentially a reflection (cannot be superimposed)

Question 18

What is a racemic mixture?

Answer 18

• A racemic mixture is a 50:50 mix of two enantiomers

- Optically inactive as the enantiomers rotate the plane of polarization of polarised light oppositely

Question 19

Why are racemic mixtures formed?

Answer 19

Racemic mixtures are formed as the likelihood of attack from above or below the planar centre is equal, creating two opposing forms of chiral molecules

Question 20

What are the products of complete combustion?

Answer 20

-H2O & CO2

Question 21

Describe the enthalpies of combustion reactions

Answer 21

• Combustion reactions give out large amounts of heat, and hence have large negative enthalpies
• The more carbons present, the greater the heat output, and the larger the negative enthalpy (but the harder they are to ignite)
• Heavily exothermic

Question 22

What is a fuel?

Answer 22

• A substance that releases heat energy when it undergoes combustion
• One which stores a large amount of energy for a small weight

Question 23

What is incomplete combustion?

Answer 23

-A combustion reaction that takes place in a limited supply of oxygen (not lack of)

Question 24

What are the products of incomplete combustion?

Answer 24

• CO & H2O

- In even less oxygen: C (soot) & H2O

Question 25

Why is incomplete combustion dangerous?

Answer 25

- The release of CO is dangerous as it is toxic. It binds to the haemoglobin in the blood in place of oxygen, preventing transportation around the body. Leads to death by asphyxiation. - CO is also odourless and colourless so is hard to detect

Question 26

What is the danger of reactions between nitrogen and oxygen in internal combustion engines?

Answer 26

- Nitrogen oxides, NOx (NO, NO2, N2O4) are produced at high temperatures - These oxides are dangerous as they can react with water vapour and oxygen in the air to form nitric acid - This nitric acid contributes to acid rain and photochemical smog

Question 27

What is the danger caused by sulfur-containing impurities in crude oil?

Answer 27

- They produce sulfur dioxide which can combine with water vapour and oxygen in the air to create sulfuric acid - This is another contributor to acid rain

Question 28

What is the danger of the production of carbon particles?

Answer 28

-Carbon 'particulates' can exacerbate asthma and cause cancer

Question 29

What is the effect of unburnt hydrocarbons on the atmosphere?

Answer 29

- They are significant greenhouse gases | - They contribute to photochemical smog (which has serious health affects)

Question 30

What is the effect of CO2 on the atmosphere?

Answer 30

- Carbon dioxide is a greenhouse gas | - Its levels are rising worryingly as it is always produced when hydrocarbons burn

Question 31

What is the effect of water vapour on the atmosphere?

Answer 31

It is a greenhouse gas

Question 32

Why is flue gas desulfurisation done?

Answer 32

- To remove sulfur dioxide given off by burning fossil fuels at power stations - Sulfur dioxide combines with oxygen and water in the atmosphere to form sulfuric acid which contributes to acid rain

Question 33

How do greenhouse gases warm the earth?

Answer 33

They trap infrared radiation from the sun so that it heats up the Earth's atmosphere?

Question 34

What are the greenhouse gases?

Answer 34

Carbon dioxide (CO2), water vapour (H2O) & methane (CH4)

Question 35

Why are greenhouse gases important?

Answer 35

Without greenhouse gases, the Earth would be too cold to sustain life

Question 36

Why has level of CO2 increased?

Answer 36

- Since the industrial revolution, fossil fuels have been used to fuel industrial plants - This releases CO2

Question 37

What is he role of water vapour in global warming?

Answer 37

- Water vapour is the most abundant of the greenhouse gases - Its levels have stayed roughly the same over the same (except locally) so has had little effect - Rising temperatures may increase water vapour however

Question 38

What are the steps of the greenhouse effect?

Answer 38

- Visible radiation from sunlight penetrates the atmosphere and warms the Earth - Invisible infra-red radiation is emitted by the Earth and cools it down, but some of this is trapped by greenhouse gases which act as a blanket

Question 39

``` An alkane containing 30 hydrogen atoms per molecule, its empirical formula is: A - C6H15 B - C7H15 C - C14H30 D - C15H30 ```

Answer 39

Answer: B (C7H15) | -Simplest ratio of C14H30 (C2 H2n+2)

Question 40

Which statement is correct about fractional distillation? A - A zeolite catalyst is used B - Each fraction contains a mixture of hydrocarbons C - Gaseous fractions are formed by breaking covalent bonds D - The fractioning column is hottest at the top

Answer 40

Answer: B