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A Level Chemistry > Organic AS > Flashcards

Organic AS Flashcards

1
Q

What are free radicals?

A

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.

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2
Q

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

A

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

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3
Q

What is the general formula of alkanes?

A

Cn H2n+2

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4
Q

What is the general formula for alkenes?

A

Cn H2n

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5
Q

Define isomer

A

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

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

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6
Q

Define structural isomerism

A

Same molecular formula but different structural formula

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7
Q

Name 3 types of structural isomerism

A

Positional
Functional group
Chain

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8
Q

What is positional isomerism?

A

The functional group is attached to the chain at different points

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9
Q

What is functional group isomerism?

A

Same molecular formula with different functional group

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10
Q

What is chain isomerism?

A

Hydrocarbon chain is arranged differently

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11
Q

What is stereoisomerism?

A

Same structural formula but different arrangement of atoms in space

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12
Q

What is E-Z isomerism?

A

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

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13
Q

Do all alkanes have isomers?

A

No, methane, methane and propane do not

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14
Q

Are alkanes polar?

A

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.

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15
Q

What is the trend of boiling points in alkanes?

A

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.

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16
Q

Are alkanes soluble?

A

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.

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17
Q

Describe the reactivity of alkanes?

A

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.

18
Q

How is acid rain produced from sulfur?

A

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.

19
Q

Describe the process of fractional distillation of crude oil

A

. 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.

20
Q

What is fracking?

A

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

21
Q

Why are some people opposed to fracking?

A

. 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

22
Q

Why is cracking useful?

A

Shorter chains are more useful

Alkenes can be produced which are more reactive

23
Q

What are the conditions for thermal cracking?

A

700-1200 K

7000 KPa

24
Q

How does thermal cracking work?

A

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.

25
Q

What are the conditions for catalytic cracking?

A

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

26
Q

What are the products of catalytic cracking?

A

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

27
Q

What does incomplete combustion produce?

A 
Carbon monoxide and water 
Sometimes carbon (soot)
28
Q

What does complete combustion produce?

A

Carbon dioxide and water

29
Q

How are nitrogen oxides produced?

A

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.

30
Q

Name some ways the atmosphere is polluted

A

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

31
Q

How is flue gas desulfurised using calcium oxide?

A

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

32
Q

What else can be used for desulfurisation?

A

Calcium carbonate (limestone)

33
Q

What is a catalytic converter?

A

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

34
Q

What is free radical substitution?

A

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

35
Q

Describe the initiation step

A

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

36
Q

Describe the propagation step?

A

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•

37
Q

Describe the termination step

A

Can happen in 3 ways:

  • Chlorine reacts together Cl• + Cl• —> Cl2
  • Methyl react together •CH3 + •CH3 —> C2H6
  • Chlorine and methyl react Cl• + •CH3 —> CH3Cl
38
Q

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

A

Cl• + O3 —> ClO• + O2

ClO• + O3 —> 2O2 + Cl•

39
Q

What is the general formula of halogenoalkanes?

A

Cn H2n+1 X

40
Q

Are halogenoalkanes polar?

A

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

41
Q

What intermolecular forces do halogenoalkanes use?

A

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

A Level Chemistry (3 decks)

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