Organic Chemistry Part 1

Question 1

What are hydrocarbons

Answer 1

Organic compounds that only contain hydrogen and carbon

Question 2

What is a homologous series

Answer 2

A family of organic compounds with the same functional group and similar chemical properties
Examples: Alkanes, alkenes etc.

Question 3

What is a functional group

Answer 3

An atom or group of atoms that give a molecules its characteristic chemical properties

Question 4

What are functional groups of alkanes, alkenes, alcohols and carboxylic acids

Answer 4

Alkanes have no functional group
Alkenes have carbon-carbon double bond
Alcohols have hydroxyl group
Carboxylic acids have carboxyl group

Question 5

What are characteristics of homologous series

Answer 5

Have same general formula
Similar chemical properties
Show gradual change in physical properties down the series from one member to the next
Successive members in series differ from each other by a -CH2- group

Question 6

How does melting and boiling point vary down a homologous series

Answer 6

The larger the relative molecular mass, higher the melting and boiling points. More energy is required to overcome the stronger intermolecular forces of attraction between the larger molecules

Question 7

How does viscosity of liquid vary down a homologous series

Answer 7

The larger the relative molecular mass, the more viscous the compound is. This is due to the stronger intermolecular forces of attraction between larger molecules

Question 8

What is a saturated compound

Answer 8

A compound containing only single bond between carbon atoms

Question 9

What is an unsaturated compound

Answer 9

A compound containing at least a double or triple bond between carbon atoms

Question 10

Name the prefixes of organic compound up to 10 (number of carbon atoms in each molecule)

Answer 10

meth-, eth, prop-, but-, pent-, hex-, hept-, oct-, non-, dec-

Question 11

How is crude oil separated in oil refinery

Answer 11

Separated into useful fractions by fractional distillation. Each fraction is mixture of hydrocarbons which boils over certain temperature range. Lighter fraction contains molecules with fewer carbon atoms and lower boiling point range than heavier fraction. Lighter fractions come out at higher ‘outlets’ of fractionating column

Question 12

Describe fractional distillation of crude oil

Answer 12

Crude oil heated to 400C in furnace and boiling takes place. Vapours passed into fractionating column. Fractionating column is hottest at bottom and cooler at top. Hot vapours rise up column, cool and condense at different heights and collected at respective outlet. Lighter fractions with lower boiling point are collected at top of column as gases. Heavier fractions with higher boiling points are collected at the bottom of the column as residue.

Question 13

Define catalytic cracking

Answer 13

A process to break down long-chain hydrocarbons into shorter chain hydrocarbons by passing the hot vapourised hydrocarbons over a heated catalyst

Question 14

What are the conditions for catalytic cracking

Answer 14

Catalyst is aluminium oxide and silicon dioxide at high temperature of about 500C to 700C. Pressure is about 1atm.
Rate of cracking and end products strongly dependent on temperature and presence of catalyst used

Question 15

What is the importance of cracking

Answer 15

Converts heavy crude oil fractions like lubricating oil which are high in supply but low in demand into lighter fractions like petrol which is low in supply but high in demand
Used to produce large amounts of shorter chain alkenes which are used to make useful chemicals (e.g. plastic, ethanol)
Cracking used to produce hydrogen, used in manufacture of ammonia in Haber process or hydrogen fuel cells

Question 16

What are issues related to competing uses of crude oil fractions

Answer 16

Non-renewable resource is used as fuel(90%) and chemical feedstock(10%)
If more crude oil used as energy source, less available for producing chemicals. Shortage of crude oil will lead to shortage of chemicals

Question 17

What are ways to conserve crude oil

Answer 17

Reduce number of motor vehicles on the road by taking public buses or MRT, driving smaller cars which consume less petrol, improve design of power stations and vehicles for efficient use of crude oil, alternative energy sources

Question 18

What are alternative fuels to crude oil

Answer 18

Biofuels - renewable energy source which comes from plants/animals, replaced relatively quickly
Bioethanol - fermentation of sugar in sugarcane plants, plants can be regrown/replaced in short period of time, burning bioethanol more environmentally sustainable, as sugar cane grows, absorbs carbon dioxide through photosynthesis, offsetting CO2 produced when bioethanol burnt

Question 19

What are issues with using bioethanol as fuel

Answer 19

Producing enough bioethanol requires significant cultivation, harvesting and transportation of sugarcane. Processes often use fossil fuels, increasing CO2 emissions. Crucial to consider CO2 generated during product and transportation when accessing environmental impact of biofuels

Question 20

What are alkanes(not a definition)

Answer 20

Saturated hydrocarbons which have the general formula CnH2n+2 (starts with n=1)

Question 21

What are the names for common side chains:
CH3
C2H5
C3H7
C4H9

Answer 21

Methyl
Ethyl
Propyl
Butyl

Question 22

What are names for common side chains:
F
Cl
Br
I

Answer 22

Fluoro
Chloro
Bromo
Iodo

Question 23

How to name branched-chain alkanes

Answer 23

Name longest carbon chain(parent chain)
Name side chain
Label position of side chain to C on parent chain
Add side chain name to parent chain
Use prefixes to indicate multiple of same type of side chains present
When there are multiple side chains, order in ALPHABETICAL order

Question 24

Define structural isomer

Answer 24

Structural isomers have same molecular formula but different structural formula
(Isomers have different properties such as melting points)

Question 25

What are physical properties of alkanes and alkenes

Answer 25

Insoluble in water, soluble in organic solvent, (melting and boiling point, viscosity from general homologous series trend0

Question 26

Describe combustion as chemical property of alkane

Answer 26

Alkanes burn readily in air when ignited by spark of flame. Combustion of alkanes are highly exothermic
Complete combustion of alkanes produces water and CO2 due to sufficient air(oxygen)
Incomplete combustion produces water and carbon/carbon monoxide due to insufficient O2

Question 27

Describe flammability of alkanes

Answer 27

Larger the relative molecular mass, less flammable the alkane becomes. As percentage of carbon present increases, it is more difficult to burn alkane. Flame produced tends to be more sooty

Question 28

Define substitution reaction

Answer 28

Involves the direct replacement of an atom in a molecule with another atom. (Alkanes react with halogens in presence of UV light.)

Question 29

Describe reaction of methane with chlorine

Answer 29

Each hydrogen atom in methane substituted one at a time by one of two chlorine atoms in Cl2. Remaining chlorine atom from Cl2 will form hydrogen chloride gas with hydrogen atom that was substituted. Other products include mixture of four types of chloromethane molecules, with relative amounts dependent upon time that reaction is allowed to proceed

Question 30

What are alkenes(not a definition)

Answer 30

Unsaturated hydrocarbons which have general formula of CnH2n (starts with n=2)

Question 31

What can you infer from number “1” in “but-1-ene”

Answer 31

The number represents location of carbon atom on parent chain where carbon-carbon double bond is located

Question 32

Describe combustion as chemical property of alkenes

Answer 32

Alkenes burn in excess air to produce carbon dioxide and water vapour. Alkenes contain relatively higher percentage of carbon than alkanes with same number of carbon atoms. Alkenes are more likely to undergo incomplete combustion, producing carbon monoxide and carbon. Alkenes burn with sootier flame than corresponding alkanes

Question 33

Describe addition reaction

Answer 33

In addition reaction, substance is added across the carbon-carbon double/triple bond in unsaturated organic compound to form new compound

Question 34

Describe hydrogenation

Answer 34

Addition of hydrogen to alkenes to form alkanes
Conditions are 180C and nickel catalyst

Question 35

What is application of hydrogenation