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AS chemistry > 6.1 nomenclature, isomerism & alkanes > Flashcards

6.1 nomenclature, isomerism & alkanes Flashcards

1
Q

describe the difference between structural formula and displayed formula when representing an organic compound.

A

structural formula - shows the arrangement of atoms carbon by carbon, with the attached hydrogen atoms, and functional groups.

displayed formula - shows how all of the atoms of the compound are arranged, including the bonds between them.

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2
Q

what does ‘nomenclature’ refer to?

A

nomenclature refers to the process of naming an organic compound.

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3
Q

define the term ‘functional group’.

A

functional group - a group of atoms in a molecule responsible for the characteristic reactions of that compound.

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4
Q

define the term ‘homologous series’.

A

homologous series - a group of organic compounds with the same functional group and general formula.

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5
Q

what is a mechanism?

A

mechanisms are diagrams that break reactions down into individual stages to show how substances react together.

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6
Q

give the three main types of mechanism.

A
  • radical substitution.
  • electrophilic addition.
  • nucleophilic substitution.
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7
Q

some mechanisms use curly arrows. explain what a curly arrow shows.

A

curly arrows show how electron pairs move when bonds are formed or broken.

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8
Q

define the term ‘nucleophile’, and give an example of a nucleophile.

A
  • nucleophiles are electron pair donors, which donate a lone pair of electrons to an ‘electron poor’ species.
  • nucleophiles are usually negatively charged ions, such as halide ions.
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9
Q

define the term ‘electrophile’, and give an example of an electrophile.

A
  • electrophiles are electron pair acceptors, which accept a pair of electrons from an ‘electron rich’ species.
  • electrophiles are often positively charged ions, such as H⁺ ions.
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10
Q

explain why radicals react with all types of species, regardless of the charge on the species.

A
  • radicals have an unpaired electron, which makes them very reactive.
  • as a result, radicals will react with all types of species; positive, negative or neutral.
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11
Q

explain why radical substitution reactions are not useful for obtaining a pure product.

A
  • because radicals react with all types of species, radical substitution reactions result in the formation of a mixture of products.
  • therefore, radical substitution reactions are not useful for obtaining a pure product.
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12
Q

what is an isomer?

A

isomers refer to structures with the same molecular formula but different atomic arrangements.

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13
Q

give the three types of structural isomer.

A
  • chain isomers.
  • positional isomers.
  • functional group isomers.
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14
Q

explain why chain isomers have similar chemical properties but different physical properties, such as melting and boiling points.

A
  • the carbon skeleton of a chain isomer can be arranged in a number of different ways.
  • these isomers have similar chemical properties, but their physical properties are different due a change in the shape of the molecule.
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15
Q

give the general formula for an alkane.

A

CₙH₂ₙ₊₂

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16
Q

alkanes are saturated hydrocarbons. explain what is meant by the term ‘saturated’.

A

saturated - refers to a molecule which only contains single carbon-carbon bonds.

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17
Q

give the general formula for a cyclic alkane.

A

CₙH₂ₙ

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18
Q

define the term ‘bond fission’.

A

bond fission - the breaking of a covalent bond.

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19
Q

describe the differences between ‘heterolytic fission’ and ‘homolytic fission’.

A

heterolytic fission

  • the covalent bond breaks unevenly, with one of the bonded atoms receiving both electrons from the bonded pair.
  • two different substances are formed - a cation and an anion.

homolytic fission

  • the covalent bond breaks evenly, and each bonding atom receives one electron from the bonded pair.
  • homolytic fission results in the formation of two electrically uncharged radicals.
20
Q

halogens react with alkanes to form halogenoalkanes in which type of reaction?

A

halogens react with alkanes in photochemical reactions.

21
Q

free radical substitution is a type of photochemical reaction in which a hydrogen atom is substituted by chlorine or bromine. give the reagent required to initiate this reaction.

A

ultraviolet (UV) light.

22
Q

give the three stages involved in a radical substitution reaction.

A
  • initiation.
  • propagation.
  • termination.
23
Q

define the term ‘photodissociation’.

A

the breaking of bonds, which lead to the breakdown of a molecule, by photons.

24
Q

radical substitution reactions result in the formation of a number of different by-products alongside the desired product. give one way in which the formation of by-products in radical substitution reactions could be reduced.

A
  • one way in which the formation of by-products could be reduced is by having an excess of methane present in the reaction.
  • an excess of methane means that there is a greater chance of a radical colliding with only a methane molecule and not a chloromethane / bromomethane molecule.
25
Q

explain why free radical substitution can result in the formation of a number of structural isomers.

A
  • free radical substitution can take place at any point along the carbon chain.
  • because of this, free radical substitution can result in the formation of a number of structural isomers.
26
Q

give the process used to separate crude oil.

A

fractional distillation.

27
Q

what is cracking?

A

the process of breaking long-chain alkanes into smaller hydrocarbons, by breaking the C-C bonds.

28
Q

give the two types of cracking used to break long-chain alkanes into short-chain alkanes.

A
  • thermal cracking.
  • catalytic cracking.
29
Q

give the conditions required for thermal cracking to take place.

A
  • a temperature of 1000°C.
  • a pressure of 70 atm.
30
Q

give the conditions required for catalytic cracking to take place.

A
  • a zeolite catalyst.
  • a temperature of 450°C.
  • a pressure of 1 atm.
31
Q

give one product of thermal cracking.

A

alkenes.

32
Q

give one product of catalytic cracking.

A

aromatic hydrocarbons.

33
Q

give one advantage of using a catalyst to ‘crack’ long-chain hydrocarbons.

A
  • using a catalyst reduces costs by speeding up the reaction.
  • performing the reaction under a low pressure and lower temperature conserves both energy and money.
34
Q

what is ‘catalytic reforming’?

A

the process of converting straight-chain alkanes into branched-chain alkanes and cyclic hydrocarbons, using a catalyst.

35
Q

give an example of a catalyst which could be used in this reaction.

A

platinum.

36
Q

give the products of complete combustion.

A

CO₂ (g) and H₂O (l)

37
Q

give the products of incomplete combustion.

A

C (s), CO (g), and H₂O (l)

38
Q

give an example of a pollutant produced from burning fossil fuels.

A

carbon monoxide (CO)

39
Q

explain how high concentrations of carbon monoxide in the bloodstream can lead to carbon monoxide poisoning.

A
  • oxygen in the bloodstream is carried by the protein complex haemoglobin.
  • carbon monoxide binds more readily to haemoglobin than oxygen does, so will bind to the haemoglobin at a much faster rate.
  • as a result, less oxygen will be able to bind to the haemoglobin, leading to oxygen deprivation and carbon monoxide poisoning.
40
Q

explain how acid rain can be caused by burning fossil fuels that contain sulphur, and give one consequence of acid rain.

A
  • acid rain can be caused by burning fossil fuels that contain sulphur.
  • the sulphur burns to produce sulphur dioxide gas, which then enters the atmosphere and dissolves in the moist air, where it is converted into sulphuric acid.
  • this falls as acid rain, which destroys trees and vegetation.
41
Q

give the name of the substance that removes pollutants from car emissions, by converting them into less harmful gases.

A

a catalytic converter.

42
Q

give an example of a catalytic converter.

A

a platinum catalyst.

43
Q

state a renewable source of energy which can be used as an alternative to fossil fuels.

A

biofuels.

44
Q

give an example of a biofuel, and explain how it is produced.

A

bioethanol is an alcohol-based biofuel made by the fermentation of sugar from crops, such as maize.

45
Q

give one advantage and one disadvantage of switching to biofuels over fossil fuels.

A

advantage

  • biofuels are renewable and can be produced over short periods of time, unlike fossil fuels which take several millennia to form.

disadvantage

  • switching to biofuels would require the modification of petrol car engines to enable them to use fuels with high concentrations of ethanol - this would be very expensive.

AS chemistry (7 decks)

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