4.2 Alcohols, haloalkanes and analysis

Question 1

alkanes vs alcohols polarity and MP/BP

Answer 1

alkanes = non-polar
non-polar bonds present as electronegativity of H and C very similar

alcohols = polar
contain polar O-H bond (high difference in electronegativity)

alcohols = higher MP/BP, lower volatility
hydrogen bond between O-H groups as well as London dispersion forces
requires more heat energy to overcome

Question 2

alkanes vs alcohols solubility

Answer 2

alkanes = insoluble
no interactions with water (polar solvent)

alcohols = soluble
can interact with water (polar solvent)
due to polar -OH group
decreases as hydrocarbon chain gets longer (influence of sole -Oh group gets smaller)

Question 3

classifying alcohols

Answer 3

primary alcohol = -OH group attached to carbon attached to just one alkyl group

secondary alcohol = -OH group attached to carbon attached to 2 alkyl groups

tertiary alcohol = -OH group attached to carbon attached to 3 alkyl groups

Question 4

combustion of alcohols

Answer 4

alcohol + oxygen -> carbon dioxide + water

Question 5

oxidation of alcohols

Answer 5

primary and secondary alcohols only
need an oxidising agent [O]
orange solution turns green

Question 6

oxidation of primary alcohols

Answer 6

primary alcohol -> aldehyde -> carboxylic acid

Question 7

conditions to prepare aldehyde

Answer 7

primary alcohol
oxidising agent
gently heat
distill at the same time to prevent further reaction with oxidising agent

Question 8

conditions to prepare carboxylic acid

Answer 8

heated strongly
under reflux (ensures all of alcohol is oxidised)
excess of oxidising agent (e.g. potassium dichromate)

Question 9

oxidation of secondary alcohols

Answer 9

secondary alcohol -> ketone

heated under reflux

Question 10

oxidation of tertiary alcohols

Answer 10

nothing happens

doesn’t undergo oxidation reactions

Question 11

dehydration of alcohols

Answer 11

heated under reflux
in presence of acid catalyst (e.g. concentrated H2SO4/H3PO4
alcohol -[catalyst]-> alkene + water

Question 12

dehydration definition

Answer 12

water molecule is removed from starting material

type of elimination reaction

Question 13

substitution reaction of alcohols

Answer 13

alcohol heated under reflux with sulfuric acid and sodium halide
NaBr(s) + H2SO4(aq) -> NaHSO4(aq) + HBr(aq)
hydrogen halide reacts with alcohol to produce haloalkane
alcohol + hydrogen halide -> haloalkane + H2O

Question 14

nucleophile definition

Answer 14

(group of) atom(s) attracted to an electron deficient centre to form a new covalent bond, electron pair donor

Question 15

why haloalkanes can attract nucleophiles

Answer 15

carbon-halogen bond is polar
carbon atom is partially positive (halogen pulls covalent pair away from carbon)
the centre of the haloalkane is electron deficient

Question 16

hydrolysis of haloalkane

Answer 16

add aqueous sodium hydroxide
nucleophile (OH-) approaches back of carbon atom (attached to halogen) opposite side to halogen
lone pair of electrons on hydroxide attracted and donated to partially positive carbon atom
new bond formed between oxygen and carbon atom
carbon-halogen bond breaks by heterolytic fission
forms alcohol and halide ion

Question 17

rate of hydrolysis and carbon-halogen bond strength

Answer 17

bond is weaker due to larger atomic radius of larger halide
lower bond enthalpy
the weaker the bond, the faster the hydrolysis (less energy required to break carbon-halogen bond)

Question 18

measuring rate of hydrolysis of primary haloalkanes

Answer 18

complete the reaction in presence of AgNO3(aq)
Ag+ ions react with halide ions produced to form precipitate
also in presence of ethanol solvent (allows water and haloalkane to mix to form single solution)
water bath

Question 19

why rate of reaction increases with haloalkanes with halogens lower down group 7

Answer 19

C-halogen bond becomes weaker with halogen lower down the group (larger atom, larger atomic radius, weaker attraction)

Question 20

use of organohalogens

Answer 20

general solvent
dry cleaning solvents
making polymers
flame retardants
refrigerants

Question 21

breakdown of ozone layer equations

Answer 21

CF2Cl2 → CF2Cl• + •Cl
•Cl + O3 → •ClO + O2
•ClO + O → •Cl + O2
overall equation: O3 + O -> 2O2

Question 22

formation of ozone

Answer 22

O2 -> 2O •

O2 + O • ⇌ O3

Question 23

what infra red does to covalent bonds

Answer 23

infra red causes covalent bonds to vibrate more and absorb energy

Question 24

factors of what frequency of infrared is absorbed by covalent bonds

Answer 24

length of covalent bond

mass of atoms on either side of bond

Question 25

why CO2, CH4 and H2O contribute to greenhouse effect

Answer 25

greenhouse gases

as C-H, O-H, C=O bonds absorb infrared radiation

Question 26

uses of IR spectroscopy

Answer 26

identify types of bonds present in unknown substances
monitor gases causing air pollution (e.g. CO and NO from car emissions)
breathalysers (measure ethanol in breath)

Question 27

fingerprint region

Answer 27

< 1500 cm^-1

contains unique peaks to find a particular molecule

Question 28

molecular ion definition

Answer 28

clear peak furthest to the right on mass spectrum
M^+
positive ion formed when a molecule loses an electron
its mass-to-charge ratio (m/z) = Mr of original molecule

Question 29

M + 1 peak

Answer 29

very small peak furthest to the right

due to larger isotope of carbon

Question 30

fragmentation definition

Answer 30

molecular ions break down into smaller pieces
forms fragment ions and free radicals
only fragment ions shown on mass spectrum as it has positive charge (radicals uncharged so not detected)

Question 31

oxidising agent foralcohols

Answer 31

acidified potassium/sodium dichromate

orange

Question 32

how nitrogen (II) oxide formed

Answer 32

combustion in engines
lightning
N2(g) + O2(g) -> 2NO(g)

Question 33

effect of nitrogen (II) oxide

Answer 33

acid rain

depletion of ozone layer

Question 34

nitrogen (II) oxide reactions for depleting ozone layer

Answer 34

•NO + O3 -> •NO2 + O2
•NO2 + O -> •NO + O2
net reaction: O3 + O -> 2O2

Question 35

how to purify organic liquid

Answer 35

separate aqueous layer from organic layer using separating funnel
dry using anhydrous salt (e.g. MgSO4, CaCl2)
redistillation

Question 36

esterification

Answer 36

when carboxylic acid and alcohol react to form ester + water

Question 37

esterification conditions

Answer 37

carboxylic acid group + hydroxyl group

concentrated sulfuric acid catalyst

Question 38

anhydrous salts examples

Answer 38

anhydrous:
CaCl2
MgSO4
CaSO4