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

AS - Unit 2 - Basic concepts and hydrocarbons Flashcards

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
How is a trans isomer (E isomer) displayed?
(E isomer) had the H atoms on each carbon on different sides
26
When naming E/Z isomers, in which order are the groups attached to the double bond named?
Based on their atomic number. | Group with the highest atomic number is given highest priority
27
What is homolytic fission?
The breaking of a covalent bond, with one of the bonded electrons going to each atom, forming two radicals
28
What is a radical?
A species with an unpaired electron
29
What is heterolytic fission?
the breaking of a covalent bond with both of the bonded electrons going to one of the atoms, forming a cation and an anion.
30
What is a nucleophile?
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
31
What is an electrophile?
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
32
What is an addition reaction?
A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule
33
What is a substitution reaction?
A reaction in which an atom or group of atoms is replaced with a different atom or group of atoms
34
What is an elimination reaction?
The removal of a molecule from a saturated molecule to make an unsaturated molecule
35
What does percentage yield measure?
The proportion of products formed in a reaction
36
What does atom economy measure?
The proportion of products that are used
37
What is fractional distillation?
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
38
How does chain length affect the boiling point of crude oil?
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
39
How does branching of alkanes affect the boiling point of crude oil?
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
40
Give a reason for longer alkane chains being dangerous to use in cars
the longer chains don't combust as easily and often undergo incomplete combustion, leaving carbon monoxide behind
41
Give two uses for short chained alkanes and alkenes
Alkane - Fuels | Alkene - Polymer production
42
What is cracking?
The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes
43
What is a catalyst?
A substance that increases the rate of a chemical reaction without being used up in the process
44
What different things are created by cracking?
Straight chain molecules into branches molecules | Straight chain molecules into cyclic molecules
45
Which kind of alkanes are most efficient in petrols?
Cyclic and branches molecules as they promote more efficient combustion than straight-chain alkanes
46
What is the H+ product of branching alkanes used for?
making margarine | ammonia production
47
What negative effects does burning hydrocarbons have on the environment?
Carbon monoxide - formed by incomplete combustion Carbon dioxide - greenhouse effect Nitrogen oxides - acid rain and destruction of forests Sulphur dioxide - acid rain
48
Explain how biofuels can help the environment
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
Which plant can be used to create biodiesel?
Rapeseed | can be used in compatible engines 100% pure but it is usually blended with normal diesel
50
What is radical substitution?
A type of substitution reaction in which a radical replaces a different atom or group of atoms
51
What is a mechanism?
A sequence of steps showing the path taken by electrons in a reaction
52
What are the three steps of radical substitution?
Initiation Propagation Termination
53
Explain the initiation stage of radical substitution
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
Explain the propagation stage of radical substitution with reference to chlorination
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
Explain the termination stage of radical substitution with reference to chlorination
Cl + Cl = Cl2 (two radicals) CH3 + CH3 = C2H6 (two radicals) CH3 + Cl = CH3Cl (two radicals)
56
What is initiation?
The first step in a radical substitution in which the free radicals are generated by ultraviolet raditation
57
What is propagation?
The two repeated steps in radical substitution that build up the products in a chain reaction
58
What is termination?
The step at the end of a radical substitution when two radicals combine to form a molecules
59
What is a pi-bond?
The reactive part of a double bond formed above and below the plane of the bonded atoms by sideways overlap of p-orbitals
60
What is a sigma bond?
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
Why is there no free rotation in a double bond?
The pi bond fixes the carbon atoms in place at either end of the double bond, preventing any free rotation
62
What is the general shape of an alkene molecule?
Trigonal planar, with an angle of 120 degrees, there are three areas of electron pair repulsion
63
What is the average bond enthalpy of a C-C single bond?
+347
64
What is the average bond enthalpy of a C=C double bond?
+612
65
Why are alkenes more reactive than alkanes?
Because of the double bond
66
What do bond enthalpies tell you?
The general strength of a bond
67
What happens to the pi and sigma bonds when an alkene reacts?
The pi bond breaks and the sigma bond remains intact
68
What are the reagents and conditions when hydrogenating an alkene?
H2, Nickel catalyst and 150 degrees C
69
What is halogenation?
When you add an X2 (halogen molecule) to an alkene to form a di-substituted halogenalkane
70
What happens when you add bromine to an alkene?
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
How do you create ethanol from ethene?
Add H2O in the form of steam and an acid catalyst
72
What is Markovnikov's rule?
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
What is electrophilic addition?
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
`What is a carbocation?
A organic ion in which a carbon atom has a positive charge
75
What is a curly arrow?
A symbol used in reaction mechanisms to show the movement of an electron pair in the breaking or formation of a covalent bond
76
How do you add HBr onto an alkene?
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
How do you add Br2 to an alkene?
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
What is used to hydrogenate and alkene?
H2 Ni catalyst 150 degrees C
79
How do you make an alcohol from and alkene?
Steam H3PO4 catalyst High temp High pressure
80
What is a polymer?
A long molecular chain built up from monomer units
81
What is a monomer?
A small molecules that combines with many other monomers to form a polymer
82
What is addition polymerisation?
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
What is an addition polymer?
A very long molecular chain, formed by repeated addition reaction of many unsaturated alkene molecules
84
Which process makes poly(phenylethene), poly(styrene) and branched poly(ethene)?
Radical polymerisation
85
When was the first margarine invented?
1909
86
When was poly(styrene) first created?
1930
87
When was PVC first created?
1938
88
What is repeat unit?
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
What is biodegradable material?
A material that is broken down naturally in the environment by living organisms
90
Give some uses for polystyrene
foam packaging | model-making in the food retail trade
91
Give some uses for poly(propene)
Food packaging dishwasher safe containers fibre in carpets synthetic ropes
92
Give some uses for polythene
Grocery bags Shampoo bottles Toys
93
What two stages are involved in recycling?
Sorting | Reclamation
94
How are plastics sorted to be recycled?
Scanning techniques to separate PET from HDPE
95
When PET bottles are recycled what are they made into?
Carpets clothing new bottles
96
When HDPE plastic is recycled what is it made into?
Re-used to make hard plastic materials such as boxes, water butts and bins
97
When LDPE plastic is recycles what is it made into?
Plastic refuse sacks
98
Some polymers are used as fuels, explain how this is possible
Burning under controlled conditions, produces heat energy can be harnessed to make electricity
99
What are biodegradable plastic bags made out of?
Starch, maize, cellulose, lactic acid
100
Give some positives of biodegradable plastics
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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