1.5- Organic chemistry

Question 0

Define saturated and unsaturated?

Answer 0

Saturated: contains single carbon-carbon bonds only

Unsaturated: contains a carbon-carbon double bond

Question 1

Define hydrocarbon?

Answer 1

Compound consisting of hydrogen and carbon only

Question 2

Define petroleum fraction?

Answer 2

Mixture of hydrocarbons with a similar chain length and boiling point range

Question 3

Define molecular formula?

Answer 3

Formula which shows the actual number of each type of atom

Question 4

Define empirical formula?

Answer 4

Shows the simplest ratio of whole number of atoms of each element in the compound

Question 5

Define general formula?

Answer 5

The algebraic formula for a homologous series e.g. CnH2n

Question 6

Define displayed formula?

Answer 6

Show all the covalent bonds present in a molecule

Question 7

Define homologous series?

Answer 7

Families of organic compounds with the same functional group and the same general formula

They show a gradual change in physical properties like boiling point

Each member differs by CH2 from the last

Same chemical properties

Question 8

Define functional group?

Answer 8

An atom or group of atoms which when present in different molecules causes them to have similar properties

Question 9

General formulae for alkanes, alkanes and haloalkanes?

Answer 9

Alkane- CnH2n+2
Alkene- CnH2n
Haloalkane- CnH2n+1X

Question 10

What are structural isomers?

Answer 10

Compounds with the same molecular formulae but different structural formulae

Question 11

Define chain isomerism?

Answer 11

Compounds with the same molecular formula but different structures of the carbon skeleton

Question 12

Define positional isomerism?

Answer 12

Compounds with the same molecular formula but different structures due to different positions of the same functional group on the carbon skeleton

Question 13

Define functional group isomerism?

Answer 13

Compounds with the same molecular formula but different structures due to atoms arranged to give different functional groups

Question 14

What is petroleum/crude oil?

Answer 14

Mixture consisting of mainly alkane hydrocarbons

Question 15

Explain the steps of fractional distillation?

Answer 15

• Crude oil is preheated and vaporised and passed into the column
• The fractions condense at different heights
• The temperature of the column decreases upwards
• The separation depends on the boiling point
• Boiling point depends on the size of molecules
• The larger the molecules the larger the van der Waals forces
• Similar molecules condense together
• small molecules condense at the top at lower temperatures and big molecules condense at the bottom at higher temperatures

Question 16

What is vacuum distillation?

Answer 16

It allows heavier fractions to be further separated without high temperatures which could break them down

Heavy residues from the fractionating column are distilled again under a vacuum

Lowering the pressure over a liquid will lower its boiling point

Question 17

What is cracking and what does it produce?

Answer 17

Conversion of large hydrocarbons into smaller molecules by breaking of C-C bonds

High Mr alkanes –> smaller Mr alkanes+ alkenes + (hydrogen)

Question 18

What are the economic reasons for cracking?

Answer 18

Shorter chain length petroleum fractions are more in demand

To make use of excess larger hydrocarbons

Products of cracking are more valuable than the starting materials

Question 19

What is thermal cracking?

Answer 19

High pressure (7000kPa) and high temperature (400-900°C)

Produces mostly alkenes (ethene used to make polythene and ethanol) and sometimes hydrogen (haber process and margarine manufacture)

Question 20

What is catalytic cracking?

Answer 20

Low pressure and high temperature (450°C) and zeolite catalyst

Produces branched and cyclic alkanes and aromatic hydrocarbons

Used to make motor fuels

Question 21

What is a fuel?

Answer 21

Something that releases energy when burnt

Question 22

What is complete and incomplete combustion?

Answer 22

Complete: in excess oxygen alkanes will burn in complete combustion producing CO2 and H2O

Incomplete: If there is a limited amount of oxygen then incomplete combustion occurs producing CO (toxic) and/or C (sooty flame)

Question 23

How is SO2 produced from burning fuels and what does it cause?

Answer 23

Sulphur impurities found in the petroleum fraction

Cause acid rain

Question 24

How can SO2 be removed?

Answer 24

Flue gas desulphurisation- waste gases pass through a scrubber containing basic calcium oxide which reacts with the acidic SO2 in a neutralisation reaction to produce Calcium sulphite

Question 25

How are nitrogen oxides produced and what do they cause?

Answer 25

Formed when N2 in the air reacts at high temperatures and spark in the engine

NO is toxic

NO2 causes acid rain

Question 26

What does CO2 contribute towards?

Answer 26

Global warming

Question 27

What do unburnt hydrocarbons cause?

Answer 27

Formation of smog

Question 28

What does soot cause?

Answer 28

Global dimming and respiratory problems

Question 29

What are catalytic converters?

Answer 29

Remove CO, NOx and unburnt hydrocarbons turning them into harmless CO2, N2 and H2O

Have ceramic honeycomb coated with a thin layer of catalyst metals platinum, palladium, rhodium to give a large surface area