core organic chemistry Flashcards
1
Q
what is a homologous series? (2)
A
1) a family of compounds with similar chemical properties
2) whose successive members differ by the addition of a CH2 group
2
Q
why does carbon form a large number of compounds? (3)
A
1) each carbon atom can form four covalent bonds
2) carbon atoms can bond to other carbon atoms to form long chains
3) bonds can be single, double or triple
3
Q
what is a saturated hydrocarbon?
A
has single carbon-carbon bonds only
4
Q
what is an unsaturated hydrocarbon?
A
contains carbon-carbon multiple bonds (double or triple)
5
Q
why is IUPAC important?
A
chemists across the globe can communicate easily
6
Q
what 3 groups can hydrocarbons the classified as? describe these groups (3)
A
1) aliphatic- carbon and hydrogen atoms are joined to each other in unbranched or branched chains, also includes cyclic organic compounds that do not contain a benzene ring (alicyclic)
2) alicyclic- carbon atoms are joined to each other in ring/ cyclic structures
3) aromatic- some or all of the carbon atoms are found in a benzene ring
7
Q
what are the three homologous series of aliphatic hydrocarbons? (3)
A
1) alkanes- containing single carbon to carbon bonds
2) alkenes- containing at least one double carbon to carbon bond
3) alkynes - containing at least one triple carbon to carbon bond
8
Q
what does the stem of the name of a compound indicate?
A
the number of carbon atoms in the longest continuous chain in the molecule
9
Q
what does the prefix of the name of a compound indicate?
A
indicates the presence of side chains or functional groups
10
Q
what does the suffix of the name of a compound indicate?
A
indicate functional groups
11
Q
what steps should you follow when naming alkanes? (4)
A
1) identify the longest continuous chain of carbon atoms/ parent chain and name it
2) identify any alkyl groups attached to the parent chain. name alkyl group and add as a prefix to the parent chain
3) add numbers before any alkyl groups to show the position of the alkyl groups on the parent chain
4) if there’s more than one, add di/ tri etc before the alkyl group
12
Q
why are the alkanes important for nomenclature?
A
The alkanes provide the basis of the naming system
13
Q
what are the stems used in naming for alkanes from 1 to 10?
A
1) meth-
2) eth-
3) prop-
4) but-
5) pent-
6) hex-
7) hept-
8) oct-
9) non-
10) dec-
14
Q
how do you name side chains in alkanes? (3)
A
1) If there are more than one of the same alkyl side-chain or functional groups, di- (for two), tri- (for three) or tetra- (for four) is added in front of its name
2) The adjacent numbers have a comma between them
3) Numbers are separated from words by a hyphen
15
Q
how do you name multiple different side chains in alkanes? e.g ethyl and methyl
A
If there is more than one type of alkyl side-chain, they are listed in alphabetic order
16
Q
what is the general formula of alkanes?
A
CnH2n+2
17
Q
how are side chains shown in the structural formula of a compound?
A
in brackets
e.g CH3CH(CH3)CH2CH3
18
Q
how do the formula of alkyl groups differ to the alkanes
A
one less hydrogen e.g
methane- CH4
methyl- CH3
19
Q
what is the functional group of alkenes?
A
C=C
20
Q
what is the general formula of alkenes?
A
CnH2n
21
Q
how do you name alkenes? (3)
A
1) determine the parent chain
2) number the parent chain using the position of the C=C double bond-must be stated for alkenes that have four or more carbons in the parent chain
3) identify any substituents/ side groups and number them
22
Q
what is the functional group of alcohols?
A
-OH
23
Q
what is the prefix of haloalkanes?
A
chloro-
bromo-
iodo-
24
Q
how do you name compounds containing functional groups? (3)
A
1) identify the longest unbranched chain of carbon atoms
2) identify any functional groups and any alkyl side chains and select the appropriate prefixes or suffixes for them
3) number any alkyl groups and functional groups to indicate their position on the longest unbranched chain
25
what is the functional group of haloalkanes?
-Cl, -Br, -I
26
what is the functional group of aldehydes?
-CHO (carbonyl group at the end of the carbon chain)
27
what is the suffix of all aldehydes?
-al
28
what is the functional group of ketones?
-C(C=O)C-/ C=O (carbonyl group is not at the end of the carbon chain)
29
what is the suffix of all ketones?
-one
30
what is the functional group of carboxylic acids?
-COOH
31
what is the suffix of all carboxylic acids?
-oic acid
32
what is the functional group of esters?
COO
33
what is the suffix of all esters?
-oate
34
what is the functional group of acyl chlorides?
-C=OCl
35
how do you name acyl chlorides?
take the name of the parent carboxylic acid and substitute -yl chloride for -ic acid where the acyl chloride substituent takes priority.
36
what is the functional group of amines?
-NH2
37
what is the functional group of nitriles?
-CN (triple bond)
38
what is general formula?
the simplest algebraic formula of a member of a homologous series e.g. for an alkane: CnH2n+2
39
what is structural formula? (2)
1) the minimal detail that shows the arrangement of atoms in a molecule e.g. for butane: CH3CH2CH2CH3 or CH3(CH2)2CH3
2) In structural formulae, the carboxyl group will be represented as COOH and the ester group as COO.
40
what is skeletal formula?
the simplified organic formula, shown by removing hydrogen atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups
41
what can R be used to represent?
alkyl groups or other fragments of organic compounds which aren't involved in reactions
42
what are structural isomers?
compounds with the same molecular formula but different structural formulae
43
what are the different ways to determine different structural formulae of a molecule? (2)
1) cut off a CH3 group and convert into a methyl group
2) move around functional group
44
what are the different types of covalent bond fission? (2)
1) homolytic fission- each bonding atom receiving one electron from the bonded pair, forming two radicals
2) heterolytic fission- one bonding atom receiving both electrons from the bonded pair forming ions
45
what is a radical and how are they represented? (2)
1) a species with an unpaired electron
2) dots are used represent species that are radicals in mechanisms
46
what is a curly arrow used for? (2)
1) shows the movement of an electron pair when bonds are being broken or made
2) showing either heterolytic fission or formation of a covalent bond
47
what is breaking a covalent bond known as?
fission
48
what is an addition reaction?
two reactants join together to form one product
49
what is a substitution reaction?
an atom or group of atoms is replaced by a different atom or group of atoms
50
what is an elimination reaction? (2)
1) involves the removal of a small molecule from a larger molecule
2) one reactant molecule forms two products
51
what is the general formula for alcohols?
CnH2n+1OH
52
what are alkanes? (2)
1) saturated hydrocarbons containing single C–C and C–H bonds as σ-bonds
2) σ-bonds have free rotation so shapes are not rigid
53
what are σ-bonds
overlap of orbitals directly between the bonding atoms
54
what is the shape and bond angle around each carbon atom in alkanes in term of electron pair repulsion? (2)
1) (3D) tetrahedral shape as each carbon atom is surrounded by four electron pairs in four σ-bonds
2) electron pairs repel to get as far apart as possible resulting in a bond angle of 109.5
55
what causes the variations in boiling points of alkanes in terms of chain length? (2)
1) compounds with a longer carbon chain length have a larger surface area as chain length increases so more surface contact is possible between molecules
2) boiling point increases as chain length increases as London forces between molecules will be greater so more energy is required to overcome these forces
56
what causes the variations in boiling points of alkanes in terms of branching? (5)
1) there are fewer surface points of contact between molecules of branched alkanes
2) fewer London forces can arise/ weaker London forces
3) branches also prevent molecules getting as close together as straight chain molecules
4) decreases London forces further
5) less energy required to overcome these forces
57
describe the reactivity of alkanes (3)
1) low reactivity of alkanes with many common reagents
2) high bond enthalpy ( C-C/C-H bonds are strong)
3) very low polarity of the σ-bonds present (C-C bonds are non polar,
C-H bond can be considered as non polar due to the similarity in electronegativity)
58
describe the complete combustion of alkanes and why they are used in fuels (3)
1) in a plentiful supply of oxygen, alkanes burn completely to produce CO2 and H2O
2) reaction gives out heat
3) alkanes burnt on a large scale and used as fuels as they readily available, easy to transport and burn in a plentiful supply of oxygen without releasing toxic products
59
describe the incomplete combustion of alkane fuels in a limited supply of oxygen with the resulting potential dangers from CO (3)
1) when oxygen is limited during combustion, the hydrogen atoms in the alkane are always oxidised to water
2) combustion of the carbon may be incomplete, forming the toxic gas carbon monoxide or carbon as soot (if asked to write an equation, assume it is carbon monoxide that forms)
3) When released into the atmosphere, these pollutants have serious environmental consequences damaging nature and health
60
what is radical substitution?
a hydrogen atom gets substituted by a halogen (chlorine / bromine)
61
how is energy provided for the radical substitution of alkanes
ultraviolet radiation in initiation step is needed for substitution reaction to occur
62
what are the 3 stages of the radical substitution of alkanes?
1) initiation- the halogen bond (Cl-Cl or Br-Br) is broken by UV energy to form two radicals in a homolytic fission reaction
2) propagation- these radicals create further radicals in a chain reaction
3) termination- the reaction is terminated when two radicals collide with each other
63
describe the initiation step of the radical substitution of alkanes (2)
1) In the initiation step the Cl-Cl or Br-Br is broken by energy from the UV radiation
2) This produces two radicals in a homolytic fission reaction
64
describe the propagation step of the radical substitution of alkanes (5)
1) The propagation step refers to the progression of the substitution reaction in a chain reaction
2) radicals are very reactive and will react with the unreactive alkanes
3) An alkyl radical is produced
4) This can react with another chlorine/bromine molecule to form the haloalkane and regenerate the chlorine/bromine radical
5) This radical can then repeat the cycle
65
describe the termination step of the radical substitution of alkanes (2)
1) the chain reaction terminates due to two radicals reacting together and forming a single unreactive molecule
2) multiple products are possible
66
what are the limitations of radical substitution? (3)
1) formation of a mixture of organic products rather than just the haloalkane
2) further substitution can occur with another radical which can continue until all hydrogen atoms have been substituted
3) reactions can occur at different positions in the carbon chain resulting in a mixture of monosubstituted isomers
67
what is the formula of cyclohexane?
C6H12
68
what are alkenes?
unsaturated hydrocarbons containing a C=C bond comprising a π-bond and a σ-bond with restricted rotation of the π-bond
69
what is a π-bond?
the sideways overlap of adjacent p-orbitals above and below the bonding C atoms
70
what is the general formula of alkenes?
CnH2n
(applies to aliphatic alkenes with one double bond and branched alkenes)
71
which alkenes do not follow the general formula? (2)
1) cyclic alkenes
2) alkenes with more than one double bond
72
describe the bonding in alkenes (5)
1) for each carbon atom of the double bond, three of the four electrons are used in 3 σ-bonds, one of which is to the other carbon atom of the double bond and the other 2 to two other atoms (carbon or hydrogen)
2) leaving one electron on each carbon atom of the double bond not involved in σ-bonds, leaving them
in a p-orbital
3) a π-bond is formed by the sideways overlap of 2 p-orbitals, so each carbon atom contributes one electron to the electron pair in the π-bond
4) Pi-electron density is concentrated above and below the line joining nuclei of the bonded atoms
5) the π-bond locks the two carbon atoms in position and prevents them from rotating around the double bond
73
describe and explain the shape of alkenes around each carbon in the C=C of alkenes (3)
1) trigonal planar shape as there are 3 bonding pairs around the carbon atom
2) bond angles of 120 degrees as these three regions of electrons will repel to get as far apart as possible
3) all of the atoms are in the same plane
74
what are stereoisomers?
compounds with the same structural formula but with a different arrangement in space
75
how does stereoisomerism arise? (3)
1) stereoisomerism around the double bond arises because rotation around the bond is restricted
2) so the groups attached to each carbon atom are fixed relative to each other
3) this is due to the position of the pi-bond's electron density above and below the plane of the sigma bond
76
what is E/Z stereoisomerism (3)
1) an example of stereoisomerism
2) molecule must have C=C double bond which results in restricted rotation about the bond
3) different groups attached to each carbon atom of the double bond
77
what is cis-trans isomerism?
1) a special case of E/Z isomerism
2) in which two of the substituent groups attached to each carbon atom of the C=C group must be a hydrogen
78
how do you distinguish which is the cis isomer and which is the trans isomer? (3)
1) cis isomer has the H atoms on each carbon in the double bond on the same side of the molecule
2) trans isomer has the H atoms diagonally opposite each other
3) in cis-trans isomerism
cis=Z isomer and trans= E isomer
79
how do you use the Cahn–Ingold–Prelog (CIP) priority rules to identify the E and Z stereoisomers? (3)
1) the higher the atomic number, the higher priority
2) if the groups of higher priority are on the same side of the double bond, the compound is the Z isomer (cis isomer)
3) if the groups of higher priority are diagonally placed across the double bond, the compound is the E isomer (trans isomer)
80
how do you assign priority if the two atoms attached to a carbon atom in the double bond are the same? (2)
1) find the first point of difference
2) the group which had the higher atomic number at the first point of difference is given the higher priority
81
outline the reactivity of alkenes (4)
1) more reactive than alkanes
2) relatively low bond enthalpy of the π-bond
3) bond is more exposed as it is found above and below the plane of the sigma bond so it is broken more readily as pi electrons are more exposed than the electrons in the sigma bond so can be easily 'attacked'
4) a pi bond readily breaks and alkenes undergo addition reactions relatively easily
82
what is the C=C bond made up of? (2)
1) a sigma bond and a pi bond
2) the pi electron density is concentrated above and below the plane of the sigma bond
83
what are the 4 addition reactions which alkenes undergo? what do each of these reactions include? (5)
1) hydrogen in the presence of a nickel catalyst at 423k
2) halogens
3) hydrogen halides
4) steam in the presence of an acid catalyst
5) each of these reactions involves the addition of a small molecule across the double bond, causing the pi bond to break and for new bonds to form
84
outline the addition reaction of alkenes with hydrogen (5)
1) alkene is mixed with hydrogen and passed over a nickel catalyst at 423k
2) an addition reaction takes place to form an alkane
3) this addition reaction, in which hydrogen is added across a double bond, I known as a hydrogenation
4) all C=C bonds react with hydrogen in this way
5) if there 2 double bonds present then two molecules of hydrogen are needed per molecule of alkene- this goes for any no. of double bonds.
85
outline the addition reaction of alkenes with halogens (3)
1) alkenes undergo a rapid addition reaction with the halogens chlorine or bromine at room temperature
2) this is known as bromination/ chlorination/ halogenation
3) this forms a dihaloakane
86
how can bromine be used to detect the presence of a double C=C bond as a test for unsaturation in a carbon chain? (4)
1) when bromine water (an orange solution) is added drowse to a sample of an alkene, bromine adds across the double bond
2) the orange colour disappears, indicating the presence of a C=C bond
3) if the same test is carried out with a saturated compound, there is no addition reaction and no colour change
4) any compound containing a C=C bond will decolourise bromine water
87
outline the addition reaction of alkenes with hydrogen halides (5)
1) alkenes react with gaseous hydrogen halides at room temperature to form haloalkanes
2) if the alkene is a gas, like ethene, then the reaction takes okay when the two gases are mixed
3) if the alkene is a liquid, then the hydrogen halide is bubbled through it
4) alkenes also react with concentrated HCl or conc. hydrobromic acid, which are solutions of the hydrogen halides in water
5) there can be two possible products if an unsymmetrical alkene reacts with an unsymmetrical molecule
88
outline the addition reaction of alkenes with steam in the presence of an acid catalyst to form alcohols (3)
1) alcohols are formed when alkenes react with steam H2O (g) in the presence of a phosphoric acid catalyst, H3PO4
2) steam adds across the double bond
3) as with the addition with hydrogen halides, there are two possible products as the H2O bonds to the alkene as two different groups- H and OH
89
define 'electrophile' (2)
1) an atom or a group of atoms that is attracted to an electron-rich centre and accepts an electron pair
2) an electrophile is usually a positive ion or a molecule containing an atom with a partial positive charge
90
define reaction mechanism
a series of steps that shows how a reaction takes place
91
what is electrophilic addition?
the mechanism which describes alkenes undergoing addition reactions to form saturated compounds
92
why does the double bond in an alkene represent a region of high electron density and what does this attract? (2)
1) because of the presence of the pi electrons
2) the high electron density of the pi electrons attracts electrophiles
93
outline the mechanism of electrophilic addition of alkene + hydrogen bromide (6)
1) bromine is more electronegative than hydrogen, so hydrogen bromide is polar and contains the dipole H+-Br-
2) the electron pair in the pi bond is attracted to the partially positive hydrogen atom, causing the double bond to break
3) a bond forms between the hydrogen atom of the H-Br molecule and a carbon atom that was part of the double bond
4) the H-Br bond breaks by heterolytic fission, with the electron pair going to the bromine atom
5) a bromide ion (Br-) and a carbocation are formed. a carbocation contains a positively charged carbon atom.
6) in the final step the Br- ion reacts with the carbocation to form the addition product
94
outline the mechanism for reaction of alkene with Br2 (8)
1) bromine is a non-polar molecule
2) when bromine approaches an alkene, the pi electrons interact with the electrons in the Br-Br bond
3) this interaction causes polarisation of the Br-Br bond, with one end of the molecule becoming becoming Brδ+ and the other end of the molecule becoming Brδ- (an induced dipole occurs)
4) the electron pair in the pi bond is attracted to the Brδ+ end of the molecule, causing the double bond to break
5) a bond has now been formed between one of the carbon atoms from the double bond and a bromine atom
6) the Br-Br bond breaks by heterolytic fission, with the electron pair going to the Brδ- end of the molecule
7) a bromide ion (Br-) and a carbocation are formed
8) in the final stage of the reaction mechanism the Br ion reacts with the carbocation to form the addition product of the reaction
95
what is Markownikoff's rule? (7)
1) each alkyl group donates and pushes electrons towards the positive charge of the carbocation
2) the positive charge is spread over alkyl groups.
3) the more alkyl groups attached to the positively-charged carbon atom, the more charge is spread out, making the ion more stable
4) tertiary carbocations most stable
5) More groups=more spread charge
6) Classified by number of R groups on +ve carbon. (R groups can represent alkyl groups)
7) Major product is one where H attaches to carbon with most H’s attached directly.
96
how are synthetic polymers named?
usually named after the monomer that reacts to form their giant molecules, prefixed by 'poly'
97
outline the addition polymerisation of alkenes
1) unsaturated alkene molecules undergo addition polymerisation to produce long saturated chains containing no double bonds
2) many different polymers can be formed, each with its own specific properties depending on the monomer used
3) industrial polymerisation is carried out at high temperatures and high pressure using catalysts
4) addition polymers have high molecular masses
98
how is the general equation presented for any addition polymerisation reaction (2)
1) N shown before reactant which signifies Manu units
2) N shown after square brackets at bottom for product
99
what is polyethene commonly used for? (3)
1) used in supermarket bags, bottles + toys.
2) depending on manufacturing
method, different densities can be made with different structures, properties + uses.
3) linear chains have a high density whereas branched chains have a low density (flexible)
100
what is polychloroethene commonly used for? (2)
1) can be made flexible/rigid
2) used for: pipes, sheeting + insulation cables
101
what is polypropene commonly used for?
toys, guttering, windows etc
102
what is polyphenylethene commonly used for?
packaging material, food trays + cups due to thermal insulating properties
103
what is polytetrafluroethene commonly used for?
coating non-stick pans, cable insulation
104
why are polymers challenging to dispose of?
Lack of reactivity→ challenge for disposal since most are non-biodegradable
105
how does recycling polymers reduce their environmental impact? (2)
1) conserves finite fossil fuels + decreases waste going in landfill.
2) have to be sorted by
type, chopped into flakes, washed, dried, melted then cut into pellet and used to make new
products
106
why is the disposal and recycling of PVC hazardous? how is this fixed? (3)
1) due to high chlorine content + range additives.
2) putting them in landfill is not sustainable & when burnt they release HCl (corrosive gas) + other pollutants.
3) new technology uses solvents to dissolve polymer, precipitates PVC from the solvent and the solvent can then be re-used
107
how can waste polymers be used as fuel? (3)
1) some polymers are difficult to recycle
2) but they high stored energy value so can be incinerated to produce heat
3) generating steam to turn turbines to produce electricity
108
what is feedstock recycling? how is it helpful? (3)
1) the chemical + thermal processes that can reclaim monomers, gases or oil from waste polymers
2) products from feedstock recycling can be used as raw materials for production of new polymers
3) Key advantage: able to handle unsorted/unwashed polymers
109
what are bioplastics and how are they advantageous? (3)
1) produced from plant starch, cellulose, plant oils + proteins
2) offer a renewable & sustainable alternative to oil-based products
3) protects environment & conserves oil reserves
110
how are biodegradable polymers broken down and how is this useful? (3)
1) broken down by microorganisms into water, carbon dioxide + biological compounds.
2) biodegradable polymers are usually made form starch/cellulose
3) Can be used as bin liners for food waste so both compost
111
what are photodegradable (oil-based) polymers and how are they broken down? (2)
1) contain bonds that are weakened by absorbing light to start degradation
2) alternatively light absorbing additives are used
112
outline the physical properties of alcohols in comparison to their corresponding alkanes (3)
1) less volatile
2) have higher melting points
3) have greater water solubility
4) differences become much smaller as the length of the carbon chain increases in alcohols
113
explain why there are differences in physical properties between alcohols and alkanes (7)
1) due to the polarity of the bonds in both the alkanes and alcohols
2) alkanes have non polar bonds due to the similarity in electronegativity between carbon and hydrogen
3) so alkane molecules are non polar
4) alkanes have very weak London forces between molecules
5) alcohols have a polar O-H bond due to the difference in electronegativity between the oxygen and hydrogen atoms
6) alcohol molecules are therefore polar
7) alcohol molecules have London forces as well as much stronger hydrogen bonds between the polar O-H groups
114
outline the solubility in water of alcohols (3)
1) alcohols can form hydrogen bonds with water so are more water-soluble than other compounds
2) as the carbon chain length increases, the influence of the OH group becomes relatively smaller
3) the solubility of alcohols decreases will chain length
115
explain the relatively low volatility of alcohols compared with alkanes (5)
1) alcohols have higher boiling points
2) in the liquid state, intermolecular hydrogen bonds hold the alcohol molecules together
3) these bonds must be broken in order to change the liquid alcohol into a gas
4) this requires more energy than overcoming the weaker London forces in alkanes
5) so alcohols have a lower volatility than alkanes with the same number of carbon atoms
116
outline the classification of alcohols into primary, secondary and tertiary alcohols and why classification is important (6)
1) classification depends on the no. of H atoms and alkyl groups/R groups attached to the carbon atom that contains OH group
2) in a primary alcohol, the -OH group is attached to a carbon atom which is attached to two H atoms and one alkyl group/ alkyl group
3) methanol is an exception
4) in a secondary alcohol, the -OH group is attached to a carbon that is attached to one H atom and two alkyl groups/ R groups
5) in a tertiary alcohol, the -OH group is attached to a carbon atom that is attached to no H atoms and three alkyl groups/ R groups
6) classification is important to predict how the alcohol will react with oxidising agents
117
which alcohols can be oxidised by an oxidising agent?
primary and secondary alcohols
118
what is the usual oxidising mixture used to oxidise alcohols? (3)
1) a solution of potassium dichromate (VI)- K2Cr2O7
2) which is acidified with dilute H2SO4
3) but the dichromate can be any element eg sodium dichromate
119
what observations would a student make if an alcohol has been oxidised by an oxidising agent?
the orange solution containing dichromate (VI) ions is reduced to a green solution containing chromium (III) ions
120
outline the oxidation of primary alcohols (2)
1) primary alcohols can be oxidised to either aldehydes or carboxylic acids
2) the product of the oxidation depends on the reaction conditions used because aldehydes are themselves oxidised to carboxylic acids
121
outline the preparation of aldehydes by the oxidation of primary alcohols (4)
1) primary alcohols must be gently heated with acidified potassium dichromate/ any dichromate to form an aldehyde
2) to ensure an aldehyde is prepared rather than a carboxylic acid, the aldehyde is distilled out of the reaction mixture as it forms
3) this prevents any further reaction with the oxidising agent
4) the dichromate (VI) ions change colour from orange to green
122
how can oxidising agents such as K2Cr2O7 be represented in an equation?
[O]
123
outline the preparation of carboxylic acids by the oxidation of primary alcohols (4)
1) primary alcohol must be heated strongly under reflux with an excess of acidified potassium dichromate (VI) to form a carboxylic acid
2) an excess of the acidified potassium dichromate (VI) must be used to ensure that all of the alcohol is oxidised
3) heating under reflux ensures that any aldehyde formed initially in the reaction also undergoes oxidation to the carboxylic acid
4) ) the dichromate (VI) ions change colour from orange to green
124
outline the oxidation of secondary alcohols (4)
1) secondary alcohols are oxidised to ketones
2) it is not possible to further oxidise ketones using acidified dichromate (VI) ions
3) to ensure the reaction goes to completion, the secondary alcohol is heated under reflux with he oxidising mixture
4) the dichromate (VI) ions change colour from orange to green
125
outline the oxidation of tertiary alcohols (2)
1) tertiary alcohols do not undergo oxidation reactions
2) the acidified dichromate (VI) remains orange when added to a tertiary alcohol
126
outline the dehydration of alcohols (4)
1) dehydration is any reaction in which a water molecule is removed from the starting material
2) an alcohol is heated under reflux in the presence of an acid catalyst such as concentrated H2SO4/ concentrated H3PO4
3) the product of the reaction is an alkene
4) dehydration of an alcohol is an example of an elimination reaction
127
outline the substitution reaction of alcohols (5)
1) alcohols react with hydrogen halides to form haloalkanes
2) the alcohol is heated under reflux with H2SO4 and a sodium halide
3) the hydrogen bromide is formed in place of the two.
4) the hydrogen bromide formed reacts with the alcohol to produce the haloalkane and water
128
exam style Q:
Oxidation if alcohol A produces butanoic acid
a) state the reagents and conditions needed to convert alcohol A into butanoic acid (2)
b) describe the colour change that would be observed during the oxidation reaction (1)
c) student changes the conditions to form an aldehyde. state two differences in the conditions that the student used (2)
a)
1) heat strongly under reflux
2) use an excess of acidified potassium dichromate as the oxidising agent
b)
1) orange to green
c)
1) aldehyde distilled out of the reaction mixture as it formed
2) excess of acidified potassium dichromate was not used
129
which haloalkanes undergo nucleophilic substitution reactions
primary and secondary haloalkanes
130
outline the mechanism of nucleophilic substitution in the hydrolysis of primary haloalkanes with aqueous alkali (6)
1) the nucleophile, OH- approaches the slightly positively charged carbon atom attached to the halogen on the opposite side of the molecule from the halogen atom
2) this direction minimises repulsion between the nucleophile and the electronegative halogen atom
3) a lone pair of electrons on the OH- ion is attracted and donated to the positively charged carbon atom
4) a new bond is formed between the oxygen atom of the hydroxide ion and the carbon atom
5) the carbon-halogen bond breaks by heterolytic fission forming a halide ion which is also a leaving group
6) the new organic product is an alcohol
131
what reagents and conditions are used for the hydrolysis of haloalkanes in a nucleophilic substitution reaction by aqueous alkali (3)
1) haloalkanes can be converted to alcohols using aqueous sodium hydroxide
2) the reaction is very slow at room temperature
3) so the mixture is heated under reflux to obtain a good yield of product
132
define the term nucleophile and give some common examples of some (4)
1) an atom or group of atoms that is attracted to an electron deficient carbon atom, where it donates a pair of electrons to form a new covalent bond
2) - hydroxide ions, OH-
- water molecules, H2O
- ammonia molecules, NH3
133
what is the hydrolysis of a haloalkane an example of?
nucleophilic substitution reaction where the halogen atom is replaced by an -OH group to form an alcohol
134
explain the trend in the rates of hydrolysis of primary haloalkanes in terms of the bond enthalpies of carbon–halogen bonds (C–F, C–Cl, C–Br and C–I) (4)
1) in hydrolysis, the carbon-halogen bond is broken and the -OH group replaces the halogen in the haloalkane
2) the rate of hydrolysis depends upon the strength of the carbon-halogen bond in the haloalkane
3) the C-F bond is the strongest carbon-halogen bond and the C-I bond is the weakest
4) less energy is required to break the C-I bond than other carbon-halogen bonds
135
outline the reactivity of carbon-halogen bonds based on their bond enthalpies
1) iodoalkanes react faster than bromoalkanes (require less energy to break)
2) bromoalkanes react faster than chloroalkanes
3) fluoroalkanes are unreactive as a large quantity of energy is required to break the C-F bond
136
outline the hydrolysis of haloalkanes in a substitution reaction by water in the presence of AgNO3 and ethanol to compare experimentally the rates of hydrolysis of different carbon– halogen bonds (13)
1) can compare the rate of hydrolysis of 3 haloalkanes: 1-chlorobutane, 1-bromobutane and 1-iodobutane
2) the rate of each reaction can be followed by carrying out the reaction in the presence of aqueous silver nitrate
3) as the reaction takes place, halide ions are produced which react with Ag+ (aq) ions to form a precipitate of the silver halide
4) the nucleophile in the reaction is water, which is present in the aqueous silver nitrate
5) haloalkanes are insoluble in water so the reaction Is carried out in the presence of an ethanol solvent
6) ethanol allows water and the haloalkane to mix and produce a single solution rather than two layers
7) for 1-chlorobutane, a white precipitate forms very slowly
8) for 1-bromobutane, a cream precipitate forms slower than 1-iodobutane but faster than 1-chlorobutane
9) for 1-iodobutane, a yellow precipitate forms rapidly
10) these results are explained by the bond enthalpies of the carbon-halogen bonds, the compound with the slowest rate of reaction is the one that has the strongest carbon-halogen bond
11) 1-chlorobutane reacts slowest as the C-Cl bond is the strongest
12) 1-iodobutane reacts fastest as the C-I bond is the weakest
13) rate of hydrolysis increases as the strength of the carbon-halogen bond decreases
137
why is ethanol used in measuring the rate of hydrolysis of primary haloalkanes? (2)
1) haloalkanes are insoluble in water so the reaction Is carried out in the presence of an ethanol solvent
2) ethanol allows water and the haloalkane to mix and produce a single solution rather than two layers
138
what is an organohalogen compound? (2)
1) haloalkane
2) molecules that contain at least one halogen atom joined to a carbon chain
139
what are some uses of organohalogen compounds?
1) flame retardants, CF3Br
2) pesticides
140
what is the ozone layer and what is its purpose? (2)
1) found at the outer edge of Earth's stratosphere
2) absorbs UV-B radiation from sun’s rays, allowing only a small amount to reach the Earth's surface
141
what are the dangers associated with the depletion of the ozone layer? (3)
1) allows more UV-B radiation to reach the Earth's surface
2) increased genetic damage
3) greater risk of skin cancer in humans
142
what happens to ozone in the stratosphere? (4)
1) ozone is continually being formed and broken down by the action of UV radiation
2) initially very high energy UV breaks oxygen molecules into oxygen radicals, O:, in the equation:
O2 --> 2O:
3) a steady state is then set up involving O2 and the oxygen radicals in which ozone forms and then breaks down
4) in this steady state, rate of formation of ozone is the same as the rate at which it is broken down, in the equation:
O2 + O --><-- O3
5) human activity, especially in the production and use of CFCs has disrupted this equilibrium
143
what happens to CFCs at the stratosphere? (3)
1) CFCs remain stable until they reach the stratosphere
2) UV breaks carbon-halogen bond by homolytic fission to form radicals
3) these radicals are thought to catalyse the breakdown of the ozone layer
144
what is photodissociation? what does it result in? (2)
1) radiation initiating break down e.g. CF2Cl2→ CF2Cl*+Cl*
2) Cl* radical which is a very reactive intermediate
145
outline the breakdown of ozone by CFCs in equations (4)
1) Propagation 1:
Cl* + O3 → ClO* + O2
2) Propagation 2:
ClO* + O→ Cl* + O2
3) Overall: O3 + O → 2O2
4) Chlorine radical generated in propagation step 2 can go on in chain reaction, breaking down 1000s molecules of ozone as it can attack and remove another molecule of ozone in propagation step 1
146
what other radicals can catalyse the breakdown of ozone?
NO radicals formed by lightning strikes + air travel in the stratosphere
147
outline the breakdown of ozone by NO radicals in equations (4)
1) propagation step 1:
O3 + NO* --> NO2* + O2
2) propagation step 2:
NO2* + O --> NO* + O2
3) Overall O3 + O → O2
4) overall equation is the same as with chlorine radicals, showing that the radicals act as a catalyst for the breakdown of ozone
148
what are three sources of CFCs in the atmosphere? (3)
1) refrigerants
2) air-conditioning
3) aerosol propellants
149
name the layer of the atmosphere above the troposphere
stratosphere
150
list the basic set quick fit apparatus (5)
1) round bottom/pear shaped flask, 2) receiver
3) screw-tap adaptor
4) condenser
5) still head
151
what is the point of heating under reflux?
1) to prepare organic liquid without boiling off solvent, reactants or products
2) enables a liquid to be continually boiled whilst the reaction takes place
152
outline the techniques and procedures for the use of Quickfit apparatus for heating under reflux (9)
1) need a heat source (Bunsen burner, tripod and gauze/ heating mantle so no naked flame which is safer/ water bath can be used rather than Bunsen if can be
carried out below 100°C)
2) anti-bumping granules added to liquid so boils smoothly
(otherwise large bubbles at bottom→ glassware vibrates + jumps)
3) glass joints greased lightly so apparatus comes apart easily after experiment
4) condensers should be clamped loosely- glass outer jacket is very fragile
5) never put stopper in top- closed system so pressure would build up & it would explode
6) rubber tubing is used to connect the inlet of the condenser to the tap and the outlet to the sink
7) water always enters the condenser at the bottom and leaves at the top to ensure that the outer jacket is full
8) the vapour from the mixture rises up the inner tube of the condenser until it meets the outer jacket containing cold water
9) the vapour then condenses and drips back into the flask
153
outline the techniques and procedures for the use of Quickfit apparatus for distillation (11)
1) method to separate a pure liquid
from its impurities
2) glass joints greased lightly so
apparatus comes apart easily after
experiment
3) flask used to collect distillate so distillation apparatus is not completely airtight
4) rubber tubing is used to connect the inlet of the condenser to the tap and the outlet to the sink
5) water always enters the condenser at the lowest point, which for distillation is the closest point to the receiver adaptor.
6) once the apparatus is set up, the flask is heated and the mixture in the flask will start to boil
7) the different liquids in the mixture will have different boiling points
8) the liquid with the lowest boiling point is the most volatile and will boil first
9) the vapour moves out of the flask up into the other parts of the apparatus, leaving behind the less volatile components of the mixture
10) when the vapours reach the cold condenser, they condense and become a liquid
11) this liquid then drips into the collecting flask
154
outline the techniques and procedures for the preparation and purification of an organic liquid by the use of a separating funnel to remove an organic layer from an aqueous layer (6)
1) if you can’t tell which is the organic layer, add water to see which layer gets bigger.
2) aqueous layer will get bigger
3) use a separating funnel once organic layer has been identified and ensure tap is closed, pour in mixture, place stopper in top + invert to mix
4) allow layers to settle (+ add water if unsure which is which)
5) place conical flask under, remove stopper + open tap until whole lower layer has left
6) collect other layer in second conical flask
155
outline techniques and procedures for the preparation and purification of an organic liquid by drying with an anhydrous salt (6)
1) traces of water are removed by adding a drying agent to the organic liquid
2) a drying agent is an anhydrous inorganic salt that readily takes up water to become
hydrated (CaCl2 (drying hydrocarbons), CaSO4 , MgSO4 )
3) add organic liquid to conical flask + add some drying agent w/ spatula + swirl
4) place stopper on to prevent product evaporating + leave for 10mins
5) if the solid has all stuck together in a lump, there is still some water present- add more drying agent until some solid is dispersed in the solution as a fine powder
6) decant the liquid from the solid into another flask. If the liquid is dry it should be clear.
156
outline techniques and procedures for the preparation and purification of an organic liquid by redistillation (3)
1) sample may still contain impurities because organic liquids have close boiling points.
2) carry out second distillation, collecting product with exact boiling point (narrower range=purer product)
3) distillation apparatus is cleaned and dried and set up again so a second distillation can be carried out
157
outline the techniques and procedures for removing acid impurities in the purification of organic products (4)
1) acid impurities can be removed by adding aqueous sodium carbonate & shaking in separating funnel
2) any acid present will react with sodium carbonate releasing CO2 gas
3) the tap needs to be slowly opened, holding the stoppered separating funnel upside down, to release any gas pressure that may build up
4) aqueous sodium carbonate layer is removed and the organic layer washed with water before running both layers off into two separate flasks
