Organic Chemistry

Question 1

Thermal cracking

Answer 1

High temperature (700°c) and high pressure (7,000 kPa)
Produces a higher proportion of alkenes
A free radical mechanism

Question 2

Catalytic cracking

Answer 2

High temperature (700K) and slight pressure involving a zeolite catalyst (aluminosilicates)
Produces motor fuels and aromatic compounds
A carbocation mechanism

Question 3

Economic reasons for cracking alkanes

Answer 3

Produces shorter chain fractions which are in higher demand (more useful/valuable)
Also produces alkenes which are more reactive

Question 4

Pollutants caused by combustion

Answer 4

Carbon monoxide, nitrogen oxides, sulfur dioxide, carbon particulates, unburnt hydrocarbons, carbon dioxide, water vapour

Question 5

Flue Gas desulfurisation

Answer 5

Calcium oxide reacts with water and SO2 to produce calcium sulfite
Calcium carbonate reacts with oxygen and SO2 to produce calcium sulfate and CO2

Question 6

Catalytic converters

Answer 6

Removes gaseous pollutants from internal combustion engines
A honeycomb coated with platinum and rhodium metals
CO, NOx and unburnt hydrocarbons react with each other

Question 7

Chlorination of alkanes

Answer 7

Free radical substitution
Need UV light and an excess of methane
Chain reactions produce a mixture of products

Question 8

Chlorofluorocarbons

Answer 8

Destroy the ozone, which protects the Earth from UV rays

Chlorine free radicals catalyse the breakdown of O3

Question 9

Reactivity of halogenalkanes

Answer 9

Increases down the group as bond enthalpy decreases

Even though bond polarity decreases

Question 10

CHEET & PAWN

Answer 10

Primary haloalkane, Aqueous solvent, Warm, Nucleophilic

Concentrated NaOH, Hot, Ethanol solvent, Elimination, Tertiary haloalkane

Question 11

Reactivity of alkenes

Answer 11

More reactive than alkanes due to the high electron density of the carbon-carbon double bond (attacked by electrophiles)

Question 12

Alkenes in steam

Answer 12

React with water to produce alcohols

Question 13

Positive inductive effect

Answer 13

Alkyl groups have a tendency to release electrons, which stabilises the positive charge of the intermediate positive carbocation
The product will tend to come from the more stable carbocation

Question 14

Poly(chloroethene)

Answer 14

Used for drainpipes

Used for aprons when plasticiser added

Question 15

Plasticisers

Answer 15

Small molecules get between the polymer chains, forcing them apart
This allows the, to slide over each other so they’re flexible

Question 16

Addition polymers reactivity

Answer 16

They’re unreactive because they have no double bonds (saturated) and strong, non-polar bonds

Question 17

Low density polythene

Answer 17

Made by polymerising ethene at high temperature and pressure
Free radical mechanism produces a chain-branching polymer
Flexible so used for packaging and electrical insulation

Question 18

High density polythene

Answer 18

Uses a Ziegler-Natta catalyst which produces less branching
Chains pack together well so high melting point
Used as milk crates, buckets and bottles (rigid)

Question 19

Recycling polymers

Answer 19

Mechanical- ground up pellets melted and reused

Feedstock- heated to produce monomers, then make new plastics

Question 20

Melting point and solubility of alcohols

Answer 20

High melting point due to hydrogen bonding
-OH group can form H-bonds with water molecules
Short chain hydrocarbons soluble in water

Question 21

Producing ethanol from crude oil

Answer 21

Ethene is hydrated with a phosphoric acid catalyst

The process is continuous, rate of reaction fast and product pure

Question 22

Producing ethanol from sugar

Answer 22

Sugar cane is fermented, and the yeast anaerobically respires to produce ethanol from glucose
35°c used so enzymes don’t denature (and no air present)
Enzymes unable to function over 15% ethanol
Batch process, slow rate of reaction and impure product (fractional distillation)

Question 23

Biofuel

Answer 23

A fuel derived or produced from renewable biological sources

Question 24

Dehydration of alcohols

Answer 24

Produces sustainable alkenes if alcohol made from fermentation
Need excess hot concentrated sulfuric acid
Alkenes used to produce addition polymers

Question 25

Carbon neutral

Answer 25

CO2 released balances CO2 absorbed

However, additional CO2 is released for the energy used to transport/process

Question 26

Solution used to oxidise alcohols

Answer 26

A solution of potassium dichromate (K2Cr2O7), acidified with dilute sulfuric acid
Dichromate turns from orange (+6) to green (+3)

Question 27

Gentle oxidation of primary alcohols

Answer 27

Less K2Cr2O7, dilute H2SO4, heated

Produces an aldehyde

Question 28

Complete oxidation of primary alcohols

Answer 28

Excess K2Cr2O7, concentrated H2SO4, reflux

Produces a carboxylic acid

Question 29

Oxidation of secondary alcohols

Answer 29

K2Cr2O7, H2SO4

Produces a ketone

Question 30

Tollen’s (silver mirror) Test

Answer 30

Tollen’s Reagent (silver nitrate in ammonia solution) contains colourless silver (I) complex ions, containing Ag+
These are reduced to metallic silver, Ag as the aldehyde is oxidised

Question 31

The Fehling’s Test

Answer 31

Fehling’s Reagent contains blue copper (II) complex ions, which are reduced to red copped (I) ions
A brick red precipitate of copper (I) oxide forms