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A-level chemistry > AS - Unit 2 - Basic concepts and hydrocarbons > Flashcards

AS - Unit 2 - Basic concepts and hydrocarbons Flashcards

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1
Q

What is a hydrocarbon?

A

An organic compound that contains carbon and hydrogen only

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2
Q

What is a saturated hydrocarbon?

A

A hydrocarbon with single bonds only

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3
Q

What is an unsaturated hydrocarbon?

A

A hydrocarbon containing carbon-to-carbon multiplde bonds

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4
Q

What is an aliphatic hydrocarbon?

A

A hydrocarbon with carbon atoms joined together in straight or branched chains

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5
Q

What is an alicyclic hydrocarbon?

A

A hydrocarbon with carbon atoms joined together in a ring structure

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6
Q

What is a functional group?

A

The part of the organic molecule responsible for its chemical reactions

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7
Q

What is a homologous series?

A

A series of organic compounds with the same functional group but with each successive member differing by CH2

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8
Q

What is an alkane?

A

A homologous series with the general formula CnH2n+2

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9
Q

What is the shape and angle of carbon atoms in an alkane?

A

A tetrahedral shape with a bond angle of 109.5

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10
Q

What is nomenclature?

A

The system of naming compounds

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11
Q

What is an alkyl group?

A

A alkane with a hydrogen atom removed e.g. CH3, C2H5. Any alkyl group is often shown as R

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12
Q

What is empirical formula?

A

The simplest whole-number ratio of atoms of each element present in a compound

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13
Q

What is molecular formula?

A

The actual number of each element in a molecule

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14
Q

How do you calculate empirical formula?

A

Divide the percentages by their elements relative formula mass
then multiply the answers by the smallest answer there
you should get a simple ratio
that is the empirical formula

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15
Q

How do you calculate molecular formula?

A

Find the relative empirical mass of the empirical formula
then divide the relative molecular mass by the relative molecular mass by the relative empirical mass
The number you are left with is how many times larger the formula is than the empirical formula

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16
Q

What is general formula?

A

The simplest algebraic formula for a member of a homolgous series

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17
Q

What is a displayed formula?

A

The relative positioning of all the atoms in a molecule and the bonds between them

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18
Q

How is structural formula useful in chemistry?

A

It shows the minimal detail for the arrangement of atoms in a molecule

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19
Q

Explain skeletal formula

A

It is a simplified organic formula, the hydrogen atoms are removed from alkyl chains, leaving just a carbon skeleton and associated functional groups

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20
Q

What are structural isomers?

A

Molecules with the same molecular formula but with different structural arrangements of atoms

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21
Q

What are stereoisomers?

A

Compounds with the same structural formula, but with different arrangement of the atoms in space

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22
Q

What is E/Z isomerism?

A

A type of stereoisomerism in which different groups attached to each carbon of a C=C double bond may be arranged differently in space because of the restricted rotation of the C=C bond

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23
Q

What is cis-trans isomerism?

A

A special type of E/Z isomerism in which there is a non-hydrogen group and hydrogen on each C of a C=C double bond.

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24
Q

How is a cis isomer (Z isomer) displayed?

A

(Z isomer) has the H atoms on each carbon on the same side

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25
Q

How is a trans isomer (E isomer) displayed?

A

(E isomer) had the H atoms on each carbon on different sides

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26
Q

When naming E/Z isomers, in which order are the groups attached to the double bond named?

A

Based on their atomic number.

Group with the highest atomic number is given highest priority

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27
Q

What is homolytic fission?

A

The breaking of a covalent bond, with one of the bonded electrons going to each atom, forming two radicals

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28
Q

What is a radical?

A

A species with an unpaired electron

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29
Q

What is heterolytic fission?

A

the breaking of a covalent bond with both of the bonded electrons going to one of the atoms, forming a cation and an anion.

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30
Q

What is a nucleophile?

A

an atom that is attracted to an electron-deficient centre or atom, where it donates a pair of electrons to form a new covalent bond

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31
Q

What is an electrophile?

A

A atom that is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond

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32
Q

What is an addition reaction?

A

A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule

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33
Q

What is a substitution reaction?

A

A reaction in which an atom or group of atoms is replaced with a different atom or group of atoms

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34
Q

What is an elimination reaction?

A

The removal of a molecule from a saturated molecule to make an unsaturated molecule

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35
Q

What does percentage yield measure?

A

The proportion of products formed in a reaction

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36
Q

What does atom economy measure?

A

The proportion of products that are used

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37
Q

What is fractional distillation?

A

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

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38
Q

How does chain length affect the boiling point of crude oil?

A

The shorter the chain the less points of contact there are between the molecules meaning there are less van der Waals’ forces holding it to other molecules, meaning less energy needed to break the bonds and thus a lower boiling point

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39
Q

How does branching of alkanes affect the boiling point of crude oil?

A

With a branched molecule there are less points of contact between molecules leading to fewer van der Waals’ forces between molecules.
Also branched molecules cant get as close to each other as unbranched molecules and therefore decreasing the intermolecular forces between the molecules and therefore lowering the boiling point

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40
Q

Give a reason for longer alkane chains being dangerous to use in cars

A

the longer chains don’t combust as easily and often undergo incomplete combustion, leaving carbon monoxide behind

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41
Q

Give two uses for short chained alkanes and alkenes

A

Alkane - Fuels

Alkene - Polymer production

42
Q

What is cracking?

A

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

43
Q

What is a catalyst?

A

A substance that increases the rate of a chemical reaction without being used up in the process

44
Q

What different things are created by cracking?

A

Straight chain molecules into branches molecules

Straight chain molecules into cyclic molecules

45
Q

Which kind of alkanes are most efficient in petrols?

A

Cyclic and branches molecules as they promote more efficient combustion than straight-chain alkanes

46
Q

What is the H+ product of branching alkanes used for?

A

making margarine

ammonia production

47
Q

What negative effects does burning hydrocarbons have on the environment?

A

Carbon monoxide - formed by incomplete combustion
Carbon dioxide - greenhouse effect
Nitrogen oxides - acid rain and destruction of forests
Sulphur dioxide - acid rain

48
Q

Explain how biofuels can help the environment

A

Ethanol can be used by fermenting sugar and other carbohydrates
it burns efficiently in a plentiful supply of oxygen to produce carbon dioxide and water
ethanol can be blended with petroleum causing the fuel to burn more efficiently.
Significantly reduced harmful exhaust emissions

49
Q

Which plant can be used to create biodiesel?

A

Rapeseed

can be used in compatible engines 100% pure but it is usually blended with normal diesel

50
Q

What is radical substitution?

A

A type of substitution reaction in which a radical replaces a different atom or group of atoms

51
Q

What is a mechanism?

A

A sequence of steps showing the path taken by electrons in a reaction

52
Q

What are the three steps of radical substitution?

A

Initiation
Propagation
Termination

53
Q

Explain the initiation stage of radical substitution

A

The bond in a chlorine molecule is broken by homolytic fission forming two chlorine radicals.
UV radiation provides the energy for this bond fission

54
Q

Explain the propagation stage of radical substitution with reference to chlorination

A

Methane reacts with the Cl radical, a methyl radical is produced and HCl is also produced
Then the methyl radical reacts with a chlorine molecule forming chloromethane and a Cl radical again

55
Q

Explain the termination stage of radical substitution with reference to chlorination

A

Cl + Cl = Cl2 (two radicals)
CH3 + CH3 = C2H6 (two radicals)
CH3 + Cl = CH3Cl (two radicals)

56
Q

What is initiation?

A

The first step in a radical substitution in which the free radicals are generated by ultraviolet raditation

57
Q

What is propagation?

A

The two repeated steps in radical substitution that build up the products in a chain reaction

58
Q

What is termination?

A

The step at the end of a radical substitution when two radicals combine to form a molecules

59
Q

What is a pi-bond?

A

The reactive part of a double bond formed above and below the plane of the bonded atoms by sideways overlap of p-orbitals

60
Q

What is a sigma bond?

A

The electrons directly bonding the atoms together, showing the overlap of orbitals, each carbon atom in a C=C bond contributes one electron to the electron pair in the sigma bond

61
Q

Why is there no free rotation in a double bond?

A

The pi bond fixes the carbon atoms in place at either end of the double bond, preventing any free rotation

62
Q

What is the general shape of an alkene molecule?

A

Trigonal planar, with an angle of 120 degrees, there are three areas of electron pair repulsion

63
Q

What is the average bond enthalpy of a C-C single bond?

A

+347

64
Q

What is the average bond enthalpy of a C=C double bond?

A

+612

65
Q

Why are alkenes more reactive than alkanes?

A

Because of the double bond

66
Q

What do bond enthalpies tell you?

A

The general strength of a bond

67
Q

What happens to the pi and sigma bonds when an alkene reacts?

A

The pi bond breaks and the sigma bond remains intact

68
Q

What are the reagents and conditions when hydrogenating an alkene?

A

H2, Nickel catalyst and 150 degrees C

69
Q

What is halogenation?

A

When you add an X2 (halogen molecule) to an alkene to form a di-substituted halogenalkane

70
Q

What happens when you add bromine to an alkene?

A

The bromine will go from orange to colourless due to the double bond breaking and the bromine now being included in the alkene to form a halogenoalkane

71
Q

How do you create ethanol from ethene?

A

Add H2O in the form of steam and an acid catalyst

72
Q

What is Markovnikov’s rule?

A

In a HX addition reaction the hydrogen of the HX becomes bounded to the carbon atom that has the greatest number of hydrogen atoms

73
Q

What is electrophilic addition?

A

A type of addition reaction in which an electrophile is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond

74
Q

`What is a carbocation?

A

A organic ion in which a carbon atom has a positive charge

75
Q

What is a curly arrow?

A

A symbol used in reaction mechanisms to show the movement of an electron pair in the breaking or formation of a covalent bond

76
Q

How do you add HBr onto an alkene?

A

HBr is polar, Br is more negative than H which causes a polar bond
Electron pain in the Pi bond is attracted to the polar H+ atom, breaking the double bond
New bond forms between one of the carbon atoms and the H atom
HBr bond breaks, electron pair going to the Bromine
Br- is formed and so is a carbocation on the alkene/alkane now
Carbocation is unstable and quickly forms a bond with the Br- ion to form an organic product

77
Q

How do you add Br2 to an alkene?

A

As the bromine approaches the pi bond, the electrons in the pi bond repel the electrons in the Br2 bond, making the Br2 slightly polar
pi bond in alkene attracted to Br+ in the Br2 which causes the double bond to break
new bond formed between one of the carbon atoms and the bromine atom
The Br-Br bond breaks by heterolytic fission leaving a Br- ion to form with the carbocation left on the organic molecule

78
Q

What is used to hydrogenate and alkene?

A

H2
Ni catalyst
150 degrees C

79
Q

How do you make an alcohol from and alkene?

A

Steam
H3PO4 catalyst
High temp
High pressure

80
Q

What is a polymer?

A

A long molecular chain built up from monomer units

81
Q

What is a monomer?

A

A small molecules that combines with many other monomers to form a polymer

82
Q

What is addition polymerisation?

A

The process in which unsaturated alkene molecules (monomers) add on to a growing polymer chain one at a time, to form a very long saturated molecular chain (the addition polymer)

83
Q

What is an addition polymer?

A

A very long molecular chain, formed by repeated addition reaction of many unsaturated alkene molecules

84
Q

Which process makes poly(phenylethene), poly(styrene) and branched poly(ethene)?

A

Radical polymerisation

85
Q

When was the first margarine invented?

A

1909

86
Q

When was poly(styrene) first created?

A

1930

87
Q

When was PVC first created?

A

1938

88
Q

What is repeat unit?

A

A specific arrangement of atoms that occurs in the structure over and over again.
Repeat units are given in brackets outside of which is the symbol ‘n’

89
Q

What is biodegradable material?

A

A material that is broken down naturally in the environment by living organisms

90
Q

Give some uses for polystyrene

A

foam packaging

model-making in the food retail trade

91
Q

Give some uses for poly(propene)

A

Food packaging
dishwasher safe containers
fibre in carpets
synthetic ropes

92
Q

Give some uses for polythene

A

Grocery bags
Shampoo bottles
Toys

93
Q

What two stages are involved in recycling?

A

Sorting

Reclamation

94
Q

How are plastics sorted to be recycled?

A

Scanning techniques to separate PET from HDPE

95
Q

When PET bottles are recycled what are they made into?

A

Carpets
clothing
new bottles

96
Q

When HDPE plastic is recycled what is it made into?

A

Re-used to make hard plastic materials such as boxes, water butts and bins

97
Q

When LDPE plastic is recycles what is it made into?

A

Plastic refuse sacks

98
Q

Some polymers are used as fuels, explain how this is possible

A

Burning under controlled conditions, produces heat energy can be harnessed to make electricity

99
Q

What are biodegradable plastic bags made out of?

A

Starch, maize, cellulose, lactic acid

100
Q

Give some positives of biodegradable plastics

A

Break down as a result of bacterial activity
Break down by biological processes composting to carbon dioxide, water, inorganic compounds, and biomass
Break down in a similar time frame as naturals compostable materials such as cellulose

A-level chemistry (15 decks)

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