Organic AS

Question 1

What are free radicals?

Answer 1

Fragments of a molecule formed when a covalent bond is broken in such a way that one electron goes to each atom. These are very reactive.

Question 2

How should u name a molecule with more than one functional group?

Answer 2

Put the prefixes in alphabetical order and also note their position

e.g 2-bromo-1-iodopropane

If there are two lots if the same use a “di” prefix

e.g 1,2-dichloroethane

Question 3

What is the general formula of alkanes?

Answer 3

Cn H2n+2

Question 4

What is the general formula for alkenes?

Answer 4

Cn H2n

Question 5

Define isomer

Answer 5

Molecules that have the same molecular formula but atoms are arranged differently.

There are two types in organic chemistry - structural isomerism and stereoisomerism

Question 6

Define structural isomerism

Answer 6

Same molecular formula but different structural formula

Question 7

Name 3 types of structural isomerism

Answer 7

Positional
Functional group
Chain

Question 8

What is positional isomerism?

Answer 8

The functional group is attached to the chain at different points

Question 9

What is functional group isomerism?

Answer 9

Same molecular formula with different functional group

Question 10

What is chain isomerism?

Answer 10

Hydrocarbon chain is arranged differently

Question 11

What is stereoisomerism?

Answer 11

Same structural formula but different arrangement of atoms in space

Question 12

What is E-Z isomerism?

Answer 12

Z isomerism = the same groups or the two highest priority molecules are on the same side of a carbon, carbon double bond
E isomerism = same groups or the two highest priority molecules are on different sides of a carbon, carbon double bond

Question 13

Do all alkanes have isomers?

Answer 13

No, methane, methane and propane do not

Question 14

Are alkanes polar?

Answer 14

Alkanes are almost non-polar as the elecetronegativity of carbon and hydrogen is so similar. This means that alkanes have weak van der waals that increase as size of the molecule increase.

Question 15

What is the trend of boiling points in alkanes?

Answer 15

Boiling points increase as chain length increases. They are gasses ar room temperature untill pentane which is a liquid then they become solids at 18 carbons. Branched alkanes have lower melting points as they cant pack closely so the van der waals arent as effective.

Question 16

Are alkanes soluble?

Answer 16

Alkanes are insoluble in water as water molecules are held together by hydrogen bonds which are stronger than van der waals. But alkanes can be soluble with relatively non-polar liquids.

Question 17

Describe the reactivity of alkanes?

Answer 17

Alkanes are relatively unreactive. They dont react with acids, bases, oxidizing reagents and reducing agents. They do burn and will react with halogens under suitable conditions.

Question 18

How is acid rain produced from sulfur?

Answer 18

When crude oil is burnt sulfur makes sulfur dioxide (SO2) which reacts with oxygen in the atmosphere making sulfur dioxide which then reacts with water in the atmosphere and makes sulfuric acid.

Question 19

Describe the process of fractional distillation of crude oil

Answer 19

. The crude oil is heated in a furnace.
. A mixture of liquids and vapours pass into a tower that is cooler at the top.
. The vapours pass up the tower via a series of trays with bubble caps untill they reach a tray at the right temperature to condense.

Question 20

What is fracking?

Answer 20

Pressurised water mixed with sand is forced init the shale causing soft rock to break and releasing trapped gas to the surface.

Question 21

Why are some people opposed to fracking?

Answer 21

. They don’t like the infrastructure
. Concern about amount of water used
. Worry about chemichemical additives polluting water supplies
. Fracking can cause small earthquakes
. Burning natural gas contributes to global warming

Question 22

Why is cracking useful?

Answer 22

Shorter chains are more useful

Alkenes can be produced which are more reactive

Question 23

What are the conditions for thermal cracking?

Answer 23

700-1200 K

7000 KPa

Question 24

How does thermal cracking work?

Answer 24

Carbon-carbon bonds break in a way that one electron goes to each carbon and two shorter chains are produced. These fragments are called free radicals which are very reactive. One will be an alkene due to limited hydrogen.

Question 25

What are the conditions for catalytic cracking?

Answer 25

720 K Low pressure but higher than atmospheric Zeolite catalyst (aluminosilicates)

Question 26

What are the products of catalytic cracking?

Answer 26

Mostly beached alkanes, cycloalkanes, and aromatic compounds. Mostly produced as gases meaning most have less than 5 carbons and usually also contains alkenes

Question 27

What does incomplete combustion produce?

Answer 27

``` Carbon monoxide and water Sometimes carbon (soot) ```

Question 28

What does complete combustion produce?

Answer 28

Carbon dioxide and water

Question 29

How are nitrogen oxides produced?

Answer 29

In petrol engines high temperatures cause nitrogen and oxygen to react which can react with water vapour and oxygen to make nitric acid which contributes to acid rain and photochemical smog.

Question 30

Name some ways the atmosphere is polluted

Answer 30

Carbon particulates = cause asthma and cancer Unburnt hydrocarbons = greenhouse gases, photochemical smog Nitrogen and sulfur oxides

Question 31

How is flue gas desulfurised using calcium oxide?

Answer 31

Calcium oxide and water is sprayed into the gas forming calcium sulfite which is oxidized to calcium sulfate which can be sold for making plaster

Question 32

What else can be used for desulfurisation?

Answer 32

Calcium carbonate (limestone)

Question 33

What is a catalytic converter?

Answer 33

Honeycomb shape coated with platinum and rhodium. The shape provides large surface area. Carbon monoxide, nitrogen oxides and unburnt hydrocarbons react with the metals to produce less harmful things like water and carbon dioxide

Question 34

What is free radical substitution?

Answer 34

One or more hydrogen atoms in the alkane are replaced by a halogen atom.

Question 35

Describe the initiation step

Answer 35

The cl-cl bond is broken. The chlorine molecule absorbs UV energy to do this. One electron goes to each atom.

Question 36

Describe the propagation step?

Answer 36

The chlorine free radical takes a hydrogen from methane leaving a methyl free radical. Cl• + CH4 ---> HCl + •CH3 The methyl free radical reacts with a chlorine making another chlorine free radical and a chloromethane •CH3 + Cl2 ---> CH3Cl + Cl•

Question 37

Describe the termination step

Answer 37

Can happen in 3 ways: - Chlorine reacts together Cl• + Cl• ---> Cl2 - Methyl react together •CH3 + •CH3 ---> C2H6 - Chlorine and methyl react Cl• + •CH3 ---> CH3Cl

Question 38

Use equations to show how CFCs are breaking down the ozone layer

Answer 38

Cl• + O3 ---> ClO• + O2 | ClO• + O3 ---> 2O2 + Cl•

Question 39

What is the general formula of halogenoalkanes?

Answer 39

Cn H2n+1 X

Question 40

Are halogenoalkanes polar?

Answer 40

They are polar as halogens are more electronegative than carbon so carbon has a partial positive and the halogen has a partial negative charge. They get less polar down the group

Question 41

What intermolecular forces do halogenoalkanes use?

Answer 41

Dipole-dipole and van der waals. The bonds aren't polar enough to them soluble in water.