5.1-5.11

Question 1

what is a hydrocarbon

Answer 1

a compound containing only hydrogen and carbon

Question 2

what’s an aliphatic compound

Answer 2

strait chained, branched or cyclic hydrocarbons that don’t contain aromatic groups

Question 3

what is an aromatic compound

Answer 3

hydrocarbons containing a benzene ring

Question 4

define ‘homologous series’

Answer 4

a series of organic compounds with the same functional group but successive members differ by CH2

Question 5

what’s carbons electron configuration and how can it form 4 single bonds

Answer 5

1s2, 2s2, 2p2. one of the electrons in the electron pair in the 2s orbital can be promoted to the 2p orbital (hybridisation). this gives four unpaired electrons that can form covalent bonds

Question 6

how can organic compounds be named

Answer 6

count the Carbons in the longest chain

name each attached alkyl group

number each carbon in the longest chain so that the first attached group has the smallest number

each alkyl group is named in alphabetical order

Question 7

what are the chemical properties of cycloalkanes

Answer 7

unreactive (due to strong non polar bonds)

react with oxygen in combustion reactions

react with halogens in the presence of UV light

Question 8

how does combustion analysis work

Answer 8

the empirical formula of a hydrocarbon can be found

the mass/volume of CO2 and H2O given off are measured

calculate the moles of CO2 and H2O. moles of C = moles of CO2. Moles of H = 2* moles of H2O.

find the smallest whole number ratio of these two values

Question 9

why is carbon monoxide poisonous

Answer 9

it binds to haemoglobin preventing oxygen from being carried around the body. this causes oxygen deprivation which can be fatal

Question 10

why does branching decrease the boiling point of hydrocarbons

Answer 10

this only applies if a branched hydrocarbon has the same molecular formula (e.g. C4H10). the branching causes molecules to be unable to pack together as tightly, reducing surface area of contact. this causes weaker induced dipole-dipole forces

Question 11

trend in physical properties of hydrocarbons

Answer 11

longer chains are less volatile and have higher viscosity. this is due to stronger induced dipole-dipole forces. they don’t dissolve in polar solvents

Question 12

what are alkenes

Answer 12

series of hydrocarbons that are unsaturated.
C=C functional group
general formula C(n)H(2n)
more reactive than alkanes

Question 13

why do alkenes have slightly lower boiling points than alkanes

Answer 13

alkenes have two fewer electrons due to the double bond. this means the induced dipole-dipole interaction is weaker

Question 14

what is an electrophile

Answer 14

an electron pair acceptor

Question 15

mechanism of electrophilic addition

Answer 15

1. arrow from C=C bond to the δ+ part of the electrophile. electrons in electrophile bond to the δ- part. (double headed arrows)
2. the C=C bond becomes a X-C-C+ where X is the δ+ part of the electrophile. the electron pair on the δ- part goes the the C+. (double headed arrow)
3. this forms X-C-C-X where X is each part of the electrophile

Question 16

what is heterolytic fission

Answer 16

the uneven split of a covalent bond. one atom receives both electrons from the bonded pair

Question 17

how can electrophiles be neutral

Answer 17

the carbon-carbon double bond induces temporary polarisation within the molecule.

Question 18

why can the electrophilic addition of alkenes produce multiple products

Answer 18

the atom from the electrophile can join either of the carbons in the double bond. e.g. the reaction of but-1-ene and HBr can form 1-bromoButane or 2-bromoButane. this only applies if the alkene is not symmetrical

Question 19

what is a carbocation

Answer 19

a molecule with a positively charged carbon ion.

Question 20

how is the major and minor product of electrophilic addition determined?

Answer 20

the major product will be the one where the carbocation has the most alkyl groups attached. this is because it’s more stable. (e.g. 1-bromoButane is the minor product and 2-BromoButane is the major)

Question 21

define polymer

Answer 21

a long chain molecule made from many smaller molecules joined together

Question 22

define monomer

Answer 22

the small molecules that join together to form a polymer

Question 23

define addition polymerisation

Answer 23

the formation of polymers from monomers joining together with no by products

Question 24

how is the display formula of polymers drawn

Answer 24

Display formula of monomers is drawn but the alkyl groups attached to the Carbons in the C=C bond are attached in structural formula form. its put in square brackets that have lines through them (represent the bonding to other monomers). there is an ‘n’ at the bottom right corner outside the brackets (represents the number of monomers in the polymer chain)

Question 25

what are plasticisers

Answer 25

molecules that push polymer chains apart. this lowers the melting point and tensile strength of the polymer but increases the flexibility.

Question 26

what's LDPE and how is it formed

Answer 26

Low density poly(ethene). 200°C and 2000atm. O2 initiator. the chains are loosely packed due to branching. its flexible and soft. used in plastic bags/cling film

Question 27

what's HDPE and how is it formed

Answer 27

high density poly(ethene). 60°C and 2atm. chains are tightly packed. its stiff and hard. used in buckets/bottles

Question 28

environmental issues of poly(ethene)

Answer 28

flammable but chemically inert strong C-C and C-H bonds no polar bonds therefore it is non-biodegradable

Question 29

issues with burning polymers

Answer 29

releases CO2 and toxic gases some can release HCl causing acid rain HCl can be removed by using a reacting with a base

Question 30

methods of dealing with waste plastics

Answer 30

burning to produce electricity melting and remoulding cracking to make monomers to make other polymers steam cracking to make alkanes/alkenes

Question 31

why are some polymers biodegradable

Answer 31

the monomers are linked by bonds that can be hydrolysed by micro-organisms

Question 32

what's a photodegradable polymer

Answer 32

a polymer that breaks down when exposed to light

Question 33

what's the H-C-H bond angle in alcohol and why

Answer 33

4 areas of electron density. all 4 are bonding pairs. tetrahedral angle of 109.5°

Question 34

what's the C-O-H bond angle in alcohol and why

Answer 34

4 areas of electron density. 2 bonding pairs, 2 lone pairs. lone pairs repel more. (109.5-2(2.5)=104.5) 104.5° angle

Question 35

how can an alcohol be named if there's another functional group

Answer 35

the OH can be noted with the prefix 'hydroxy-' | e.g. 2-hydroxy propanoic acid

Question 36

whats the difference between primary, secondary and tertiary alcohols

Answer 36

the number of alkyl groups attached to the carbon that the alcohol group is attached to. for 1° alcohols its 1 alkyl group and for 2° alcohols its 2

Question 37

why do alcohols have higher boiling points than alkanes

Answer 37

they can form hydrogen bonds and have a permanent dipole-dipole interaction. (both have induced interaction)

Question 38

how does solubility change as the chain length of alcohols increases

Answer 38

solubility decreases as chain length increases because more energy is required as the induced dipole-dipole interaction will be stronger

Question 39

what chemicals are used to oxidise alcohols

Answer 39

potassium dichromate and dilute sulphuric acid

Question 40

half equation of dichromate ions oxidising alcohol

Answer 40

14H+ + 6e- + Cr2O7^2- --> 2Cr^3+ 7H2O

Question 41

what's an aldehyde

Answer 41

they contain the C=O functional group at the end of the chain. compounds end with the suffix -al. (e.g. propanal) there's no number as C=O is always at the end

Question 42

what's a ketone

Answer 42

they contain the C=O functional group but not at the end of the chain. compounds end with suffix -one. (e.g. propanone or pentan-3-one) number only needed if carbon chain is 5 or more

Question 43

why are tertiary alcohols not easily oxidised

Answer 43

the carbon atom that's attached to the -OH group has no hydrogens available for oxidation

Question 44

what's the colour change when oxidising alcohols and why

Answer 44

orange to green Cr2O7 ^2- ions are yellow Cr^3+ ions are green

Question 45

what's the relative boiling points of aldehydes, ketones, carboxylic acids and alcohols and why

Answer 45

alcohols and carboxylic have higher B.Ps as they have I.D.D, P.D.D and H.B. ketones and aldehydes have lower boiling points as they only have I.D.D and P.D.D

Question 46

what is heating under reflux

Answer 46

a condenser is placed vertically onto the flask containing the mixture. this prevents any substances from boiling and escaping. instead they condense and return to the flask

Question 47

how can alcohols be completely oxidised into a carboxylic acid

Answer 47

add excess potassium dichromate. add anti-bumping granules. reflux gently (prevents aldehyde from escaping to ensure complete oxidation). purify using distillation.

Question 48

how can alcohols be partially oxidised into an aldehyde

Answer 48

add excess potassium dichromate. add anti-bumping granules. immediately distil off the aldehyde. this ensures only partial oxidation. collect in an ice bath (aldehydes have low boiling points)

Question 49

define 'homolytic fission'

Answer 49

when a covalent bond breaks and each atom receives one electron from the bonding pair, forming two radicals