organic chem

Question 1

homologous series and functional groups

Answer 1

alkanes
-CnH2n+2

alkenes
-carbon-carbon double bond
-CnH2n

alcohols
-hydroxyl OH
-CnH2n+1OH

carboxylic acids
-carboxyl COOH
CnH2n+1COOH

Question 2

IUPAC naming

Answer 2

-longest carbon chain with principal functional group should be named as the stem
-number the chain starting from principal functional group/ such that the overall numbering of the substituents are the lowest numbers
-if there are multiple substituents to be named in the prefix, name the substituents in alphabetical order
-if there are more than 1 of the same substituent on the same carbon atom, ‘di-‘, ‘tri-‘ and ‘tetra-‘ are used

Question 3

names of stem

Answer 3

1 meth-
2 eth-
3 prop-
4 but-
5 pent-
6 hex-
7 hept-
8 oct-
9 non-
10 dec-

Question 4

name of substituents

Answer 4

-CH3 methyl
-C2H5 ethyl
-C3H7 propyl
-C4H9 butyl
-C5H11 pentyl
-F fluoro
-Cl chloro
-Br bromo
-I iodo

Question 5

fractional distillation of petroleum/ crude oil

Answer 5

-lighter fractions with fewer number of carbon atoms have lower boiling points, collected at the top
-heavier fractions with greater number of carbon atoms have higher boiling points, collected at the bottom

uses of petroleum fractions
-petroleum gas collected at the top used for fuel for cooking and heating
-petrol used for fuel for car engines
-naphtha used for chemical feedstock for making petrochemicals like plastics and detergents
-kerosene used for fuel for aircraft engines
-diesel used for fuel for diesel engines
-lubricating oil used for lubricant machines, making waxes and polishes
-bitumen used for making road surfaces and roofing

Question 6

uses and how to conserve petroleum

Answer 6

-90% used as fuel to generate heat and electricity, powers motor vehicles and industrial activities
-10% used as feedstock for manufacture of plastics, medicines, fertilisers, pesticides and synthetic rubber

to conserve petroleum
-reduce the use of petroleum
-use alternative energy sources such as biofuel, solar energy and nuclear energy
-design power stations and vehicles that use petroleum more efficiently

Question 7

physical properties of alkanes

Answer 7

as Mr increases,
-melting and boiling points increases. stronger intermolecular forces between molecules as number of electrons increases.
-density increases
-viscosity increases
-flammability decreases
-insoluble in water, but soluble in organic solvents

Question 8

chemical properties of alkanes

Answer 8

-complete combustion forms water vapour and carbon dioxide
-incomplete combustion forms water vapour, carbon dioxide, carbon and/ or carbon monoxide

substitution reaction
-reagents - generally Cl2(g) or Br2(g)
-conditions - uv light, provides activation energy
-observations - greenish-yellow Cl2 turns colourless or reddish-brown Br2 turns colourless
-HCl/ HBr(g) formed

Question 9

physical properties of alkenes

Answer 9

as Mr increases,
-melting and boiling points increases. stronger intermolecular forces between molecules as number of electrons increases.
-density increases
-viscosity increases
-flammability decreases
-insoluble in water, but soluble in organic solvents

Question 10

physical properties of alkanes vs alkenes

Answer 10

-melting and boiling point of alkenes is slightly lower than alkanes with the same number of carbon atoms
-each alkene has fewer electrons than corresponding alkane with the same number of carbon atoms, hence weaker intermolecular forces between molecules

Question 11

catalytic cracking of long chain hydrocarbons

Answer 11

-reagents - long chain alkane
-conditions - high temperature, finely divided SiO2 or Al2O3 catalyst

purpose of catalytic cracking
-produce hydrogen for haber process and hydrogen fuel cell
-produce short chain alkenes as raw material for making alcohols like ethanol and plastics like poly(ethene)
-produce short chain alkanes that are generally higher in demand than longer chain alkanes

Question 12

chemical properties of alkenes

Answer 12

-complete combustion forms water vapour and carbon dioxide
-incomplete combustion forms water vapour, carbon dioxide and carbon and/ or carbon monoxide

addition reactions
-saturated organic compounds are alkanes with single carbon-carbon bonds
-unsaturated organic compounds are alkenes with double or triple carbon-carbon bonds

Question 13

addition of hydrogen

Answer 13

-reagents - hydrogen
-conditions - 200ºc, nickel catalyst
-used to convert unsaturated fats to saturated fats, eg. hydrogenation of vegetable oil to form margarine

Question 14

addition of bromine

Answer 14

-reagents - Br2(l)
-conditions - in the dark to prevent substitution reaction from occurring
-observations - reddish brown bromine turns colourless

Question 15

addition of steam

Answer 15

-reagents - steam
-conditions - 300ºc, 65 atm, H3PO4 catalyst
-produces alcohol

Question 16

addition of hydrogen halides

Answer 16

-reagents - hydrogen halides, eg. HF, HCl, HBr, HI
-conditions - room temperature

Question 17

addition polymerisation

Answer 17

-reactants - alkene monomer
-conditions - high temperature and pressure, presence of catalyst

Question 18

physical properties of alcohols

Answer 18

as Mr increases,
-melting and boiling points increases. more energy required to overcome the stronger intermolecular forces of attraction between molecules as number of electrons increases.
-density increases
-viscosity increases
-flammability decreases
-solubility in water decreases

Question 19

production of alcohols

Answer 19

addition of steam to alkenes
-reagents - steam
-conditions - high temperature and pressure (300ºc, 65 atm), H3PO4 catalyst

fermentation of glucose to produce ethanol
-equation - C6H12O6 —> 2C2H5OH + 2CO2
-reagents - C6H12O6
-conditions - room temperature (optimal temperature for yeast, above will be denatured), absence of oxygen (for anaerobic respiration, as aerobic respiration may lead to ethanol oxidising to ethanoic acid), yeast, water
-separate ethanol from mixture by fractional distillation

Question 20

chemical properties of alcohols

Answer 20

-complete combustion forms water vapour and carbon dioxide
-incomplete combustion forms water vapour, carbon dioxide, carbon and carbon monoxide

oxidation with acidified KMnO4
-reagents - acidified potassium manganate (VII) solution
-conditions - heat under reflux
-observations - purple acidified potassium manganate (VII) solution turns colourless
-alcohol becomes a carboxylic acid

oxidation with oxygen and bacteria in air
-reagents - oxygen
-conditions - presence of bacteria
-alcoholic drinks turn sour when exposed to air and bacteria for some time due to formation of ethanoic acid

Question 21

physical properties of carboxylic acids

Answer 21

-carboxylic acids are weak acids, have a sour taste, conduct electricity when dissolved in water due to mobile ions and turn moist blue litmus paper red

as Mr increases,
-melting and boiling points increases. more energy required to overcome the stronger intermolecular forces of attraction between molecules as number of electrons increases.
-density increases
-viscosity increases
-flammability decreases
-solubility in water decreases

Question 22

production of carboxylic acids

Answer 22

oxidation of alcohols with acidified KMnO4
-reagents - acidified potassium manganate(VII) solution
-conditions - heat under reflux
-observations - purple acidified potassium manganate(VII) solution turns colourless

oxidation of alcohols with oxygen and bacteria in air
-reagents - oxygen
-conditions - presence of bacteria

Question 23

chemical properties of carboxylic acids

Answer 23

-complete combustion forms water vapour and carbon dioxide
-incomplete combustion forms water vapour, carbon dioxide, carbon and carbon monoxide

-acid + base —> salt + water
-acid + reactive metal —> salt + hydrogen
-acid + carbonate —> salt + carbon dioxide + water
-ethanoic acid (ionises partially) —> ethanoate ion and hydrogen ion

Question 24

condensation reaction/ esterification

Answer 24

-reagents - alcohol and carboxylic acid
-conditions - heat under reflux, concentrated H2SO4 (catalyst, acts as a dehydrating agent to remove water)
-remove H2O
-reverse reaction of esterification is hydrolysis (requires addition of H2O)

esters
-generally have a sweet smell
-used for artificial food flavouring, perfumes, cosmetics, etc.
-name the alcohol part first (H removed) then the acid part (OH removed), eg. methyl ethanoate

Question 25

acidic hydrolysis of esters

Answer 25

-reagents - dilute acid such as HCl
-conditions - heat under reflux

Question 26

structure of polymers

Answer 26

-strong covalent bonds between atoms
-weak intermolecular forces between different polymers (overcome during melting/ boiling)

Question 27

addition polymerisation

Answer 27

-unsaturated monomers join together without the loss of any molecules or atoms to form a polymer
-reactants - alkene monomer
-conditions - high temperature and pressure, catalyst
-uses of poly(ethene) - plastic bottles, plastic bags, clingfilm

Question 28

condensation polymerisation

Answer 28

-molecules combine to form a polymer, with the loss of small molecules such as water or hydrogen halide

formation of nylon
-nylon is a polyamide because it contains a large number of amide linkages
-reactants - diamine + dicarboxylic acid
-amide linkage refers to HNCO
-uses - clothings, parachutes, fishing, rain coats

formation of terylene
-terylene is a polyester because it contains a large number of ester linkages
-reactants - diol + dicarboxylic acid
-ester linkage refer to COO
-uses - clothings, curtains, sleeping bags

-condensation polymers can be hydrolysed using dilute acid/ alkali and high temperature to form back monomers

Question 29

advantages and disadvantages of plastics

Answer 29

advantages
-light, tough and waterproof
-durable (resistant to decay, corrosion and chemical reaction)
-easily moulded into different shapes

disadvantages
-plastics are non-biodegradable hence cannot be broken down by bacteria and other decomposes
-land pollution - disposal in landfill leads to increasing amount of build-up waste
-air pollution - some plastics produce poisonous gases such as HCl when burnt
-water pollution - improper disposal endangers marine animals, mistake the plastics for food
-non-renewable source