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Chemistry - Energy, Chains & Resources > Alkanes, Alkenes & Alcohols > Flashcards

Alkanes, Alkenes & Alcohols Flashcards

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0
Q

Crude oil consists of…

A

Many hydrocarbons, most of which are unbranched alkanes

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1
Q

Hydrocarbon definition

A

A compound of hydrogen and carbon only

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2
Q

Fractional distillation definition

A

The separation of the components in a liquid mixture into fractions which differ in boiling point by means of distillation, typically using a fractioning column

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3
Q

What are hydrocarbons gained from fractional distillation used for?

A

Petrol, kerosene, heating and lubricating oils

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4
Q

What 3D shape occurs around each carbon atom in alkanes?

A

Tetrahedral

Each carbon is bonded to 4 other groups of atoms and has no lone pairs

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5
Q

Explain the effect of chain length on the boiling points of alkanes

A

As the chain length increases, the boiling point increases because the van der Waals’ forces between molecules gets stronger. In longer chain alkanes, there are more points of contact between the molecules. More energy is needed to overcome these forces.

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6
Q

Explain the effect of branching on the boiling point of alkanes

A

A branched alkane has a lower boiling point than an unbranched alkane because there is a smaller contact area between molecules, so the van der Waals’ forces are weaker. Less energy is required to overcome these forces.

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7
Q

Describe the combustion of alkanes

A

Short-chain alkanes burn in a plentiful supply of oxygen to form carbon dioxide and water

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8
Q

What is methane used for?

A

Domestic heating and cooking

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9
Q

What are propane and butane used for?

A

Fuels in barbecues, patio heaters and portable cooking appliances

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10
Q

Cracking definition

A

The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes

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11
Q

Why is cracking necessary?

A

Short chain hydrocarbons are in much higher demand than long chain hydrocarbons. They are used in fuel and in polymer production

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12
Q

What does isomerisation do?

A

Converts unbranched alkanes into branched alkanes

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13
Q

What does reforming do?

A

Converts straight chained alkanes into cyclic hydrocarbons

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14
Q

Why are reforming and isomerisation necessary?

A

Branched and cyclic alkanes are important petrol additives as they promote more efficient combustion than straight-chain alkanes. They are used extensively in fuels for car engines.
The hydrogen produced in reforming is also used in other chemical processes such as ammonia production and margarine production

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15
Q

What are petrochemicals?

A

Items that can be made indirectly from crude oils. Eh plastics, cosmetics, dyes and inks

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16
Q

Burning hydrocarbons leads to an increase in atmospheric pollutants, such as…

A

Carbon monoxide - a toxic gas formed by incomplete combustion in the internal combustion engine
Carbon dioxide - a major contributor to climate change via the greenhouse effect
Nitrogen oxides - contributors to acid rain and destruction of forests
Sulfur dioxide - a contributor to acid rain

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17
Q

Radical definition

A

A species with an unpaired electrons

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18
Q

What is a biofuel?

A

A fuel that is derived from recently living material such as plants, or from animal waste

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19
Q

Describe the reaction between methane and chlorine to form chloromethane and hydrogen chloride

A

CH4 + Cl2 –> CH4Cl + HCl
This is free radical substitution.
Initiation: UV radiation causes the Cl-Cl bond to break homolytically, forming 2 Cl radicals. Cl2 –> Cl• + Cl•
Propagation: methane reacts with a chlorine radical. A single C-H bond is broken by homolytic fission, forming a methyl radical. Hydrogen chloride is also formed. CH4 + Cl• –> •CH3 + HCl
The methyl radical then reacts with another chlorine molecule.
•CH3 + Cl2 –> CH3Cl + Cl•
This choline radical can be used again the the first propagation step.
Termination: 2 radicals combine to form a molecule. Eg Cl• + Cl• –> Cl2

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20
Q

What are the limitations of free radical substitution?

A

It is a reaction that is very hard to control. Many radicals form and there are a lot of possible products. Hydrogen atoms can keep being replaced by other atoms.

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21
Q

Saturated hydrocarbons…

A

Contain carbon to carbon single bonds only

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22
Q

Unsaturated hydrocarbons…

A

Contain carbon to carbon multiple bonds

23
Q

How is a π bond formed?

A

A π bond is formed above and below the plane of the carbon atoms by sideways overlap of p-orbitals. Each carbon atom contributes one electron from a p-orbital to the electron pair in the π bond

24
Q

What shape surrounds each carbon atom in alkenes?

A

Trigonal planar

There are 3 regions of electron density around each carbon atom in the double bond and no lone pairs

25
Q

Describe the reaction that turns alkenes into alkanes

A

Hydrogen gas and a gaseous alkene are passed over a nickel catalyst at 150 * C
This reaction is called hydrogenation
The hydrogen adds across the double bond and an alkane is formed

26
Q

Describe the reaction that turns alkenes into di-halogenoalkanes

A

Alkenes react rapidly with halogens at room temperature
This reaction is halogenation
The halogen adds across the double bond to give a di-substituted halogenoalkane

27
Q

How would you test for a carbon to carbon double bond

A

Add bromine

The mixture will turn from orange to colourless if a carbon to carbon double bond is present

28
Q

Describe the reaction that turns alkenes into alcohols

A

Steam and the gaseous alkene are heated to a high temperature and pressure in the presence of a phosphoric acid catalyst
This reaction is the hydration of an alkene

29
Q

Electrophile definition

A

A species capable of accepting a pair of electrons

30
Q

Describe the addition of hydrogen bromine to ethene

A

Hydrogen bromide is a polar molecule. Bromine is more electronegative that hydrogen, this causes a dipole:
δ+Η-Brδ-
The electron pair in the π bond is attracted to the slightly positive hydrogen atom, causing the double bond to break
A new bond forms between one of the carbon atoms and the hydrogen atom
The H-Br bond breaks by heterolytic fission, with the electron pair going to the bromine
A bromide ion (Br-) and a carbocation are formed
The positively charged carbocation is unstable and quick reacts with the bromide ions to form bromoethane

31
Q

Repeat units are always…

A

2 carbons long

32
Q

Addition polymerisation definition

A

The process in which unsaturated alkene molecules add on to a growing chain one at a time, to form a very long saturated molecular chain

33
Q

Describe the use of alkenes in the manufacture of margarine

A

Hydrogenation is used to harden vegetable oils (containing long, polyunsaturated hydrocarbon chains)
This adds hydrogen molecules across double bonds in an addition reaction
A nickel catalyst is used
This alters the individual molecule in such a way that the oil partially solidifies and hardens

34
Q

Outline 3 ways of processing waste polymers

A

Sorting and recycling
Combustion for energy production
Can be cracked into other monomers

35
Q

Why are waste polymers a problem?

A

They are not biodegradable
Combusting them produces CO2, which is a greenhouse gas and contributes to climate change
Landfill sites are rapidly filling - there will soon not be any more space to store them

36
Q

How are chemists minimising environmental damage created by waste polymers

A

Removing toxic waste products (eg HCl) formed during disposal by combustion of halogenated plastics
Developing biodegradable and combustible polymers from isoprene, maize and starch

37
Q

Describe the process of producing ethanol by fermentation of glucose

A

Fermentation is carried out at around 37*C, in the presence of yeast (enzymes in the yeast catalyse the reaction). It is important it is carried out in the absence of air
C6H12O6 –> 2CH3CH2OH + 2CO2

38
Q

Describe the process of producing ethanol by hydration of ethene

A

This process uses steam and a phosphoric acid catalyst, and is carried out at a high temperature and pressure
CH2=CH2 + H2O –> CH3CH2OH

39
Q

Explain the relatively high boiling points (and thus low volatility) of alcohols

A

Alcohols have hydrogen bonds which is the strongest type of intermolecular force

40
Q

Describe and explain the solubility of the alcohols

A

Solubility decreases as the chain length increases
This is because the hydrocarbon chain does not form bonds with water molecules. As the chain length increases, a larger part of the alcohol molecule is made up of a non-polar hydrocarbon chain

51
Q

What conditions are needed for hydrogenation?

A

Nickel catalyst, high temperature and pressure

52
Q

What conditions are needed for the reaction between ethene and steam?

A

Phosphoric acid catalyst, high temperature

53
Q

What conditions are needed for the reaction between ethene and bromine?

A

High temperature

85
Q

State the uses of ethanol

A

Used in alcoholic drinks and as a solvent in the form of methylated spirits

86
Q

State the uses of methanol

A

As a petrol additive to improve combustion and as an important feedstock for the production of methanol and ethanoic acid

87
Q

What is produced when a primary alcohol is heated gently, an oxidising agent is added and it is distilled immediately?

A

An aldehyde + H2O

88
Q

What is produced when a primary alcohol is sheathed strongly under reflux and an excess of oxidising agent is added?

A

A carboxylic acid + H2O

89
Q

During the oxidation of primary and secondary alcohols, what colour change occurs?

A

The oxidising agent turns from orange to green

90
Q

What is produced when a secondary alcohol is heated under reflux and an oxidising agent is added?

A

A ketone

91
Q

What catalyst is used in esterification?

A

A concentrated sulfuric acid catalyst

92
Q

How would esterification be carried out?

A

In a boiling tube, add 1cm^3 of the carboxylic acid to 1cm^3 of the alcohol
Add a few drops of concentrated sulfuric acid catalyst
Place the boiling tube in a water bath at about 80*C for 5 minutes
Pour the product into a beaker of cold water

93
Q

What is the name of the ester produced from ethanoic acid and methanol?

A

Methyl ethanoate

94
Q

Describe the dehydration of alcohols

A

The alcohol is heated under reflux with a concentrated sulfuric acid catalyst to form an alkene and water

95
Q

Explain why many industrial processes use catalysts

A

Reactions can happen at a lower temperature
This saves energy costs
Reduces carbon dioxide emissions
Enable reactions to take place with a higher atom economy

Chemistry - Energy, Chains & Resources (6 decks)

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