Organic Chemistry

Question 1

What is the empirical formula? How is it related to molecular formula?

Answer 1

Simplest whole-number ratio of atoms of different elements in the compound.
The two are related by some numerical constant.
E.g. the empirical formula for heptene, C7H14, is CH2. Multiplying the empirical formula by a numerical constant (7) would yield the molecular formula of heptene

Question 2

What is crude oil?

Answer 2

Crude oil is a mixture of compounds; a fossil fuel consisting of the remains of ancient biomass.
Finite resource - cannot be replaced as it is used up.

Question 3

What is a hydrocarbon?

Answer 3

A compound made up exclusively of hydrogen and carbon atoms

Question 4

What are alkanes?

Answer 4

Saturated hydrocarbons of a general formula CnH2n+2

Question 5

What is a homologous series?

Answer 5

Series of compounds with same general formula, same functional groups and similar chemical properties.

Question 6

Describe the combustion of hydrocarbons

Answer 6

Exothermic reaction occurring when hydrocarbons are reacted with oxygen.
Complete combustion produces carbon dioxide and water (carbon and hydrogen atoms are completely oxidised).
Incomplete combustion produces carbon or carbon monoxide and water.

Question 7

Describe the physical properties of alkanes

Answer 7

• First few in series are gases, then change to liquids, then to solids.
• In general, boiling points and viscosity increase as molecules get bigger; volatility and flammability decrease as molecules get bigger.
• Poor reactivity.

Question 8

Explain how fractional distillation of crude oil takes place

Answer 8

• Crude oil is heated and vaporised.
• Vapor rises up the fractionating column (tower).
• The column is hotter at the bottom and cooler at the top.
• Hydrocarbons cool as they go up the column and condense at different heights, as they have different boiling points.
• Large molecules, high boiling points - collected at the bottom.
• Small molecules, low boiling points - collected at the top.
• This gives fractions, which can be used in various ways.

Question 9

What is cracking?

Answer 9

When large hydrocarbons are thermally broken down into smaller and useful molecules.

Question 10

What type of reaction is cracking?

Answer 10

Thermal decomposition

Question 11

What are the conditions for cracking?

Answer 11

Reactant heated to vapor, passed over a hot catalyst (catalytic cracking) or heated to vapor, mixed with steam and heated to high temperatures (steam cracking)

Question 12

How are the products of cracking used?

Answer 12

The products are alkanes and alkenes – used as polymers and starting materials for synthesis.

Question 13

What is an alkene?

Answer 13

Unsaturated hydrocarbon. Contains at least one C=C bond. General formula for alkenes is:
CnH2n.

Question 14

What is the test for alkenes?

Answer 14

Add bromine water. Colour change occurs from orange to colourless.

Question 15

Describe the combustion of alkenes

Answer 15

They burn with smoky flames due to incomplete combustion.

Question 16

Describe addition reactions of alkenes

Answer 16

Question 17

What is an alcohol?

Answer 17

An organic compound that contains an -OH functional group.

Question 18

State characteristics of methanol, ethanol, propanol and butanol

Answer 18

• Dissolve in water to form a neutral solution.
• React with sodium to form hydrogen.
• Burn in oxygen.
• React with carboxylic acids in presence of acid catalyst to form esters.

Question 19

Oxidation of the alcohols leads to…?

Answer 19

Carboxylic acids.

Question 20

What are some uses of alcohols?

Answer 20

• Fuels
• Solvents
• Drinks

Question 21

State the conditions required for fermentation of glucose and state the equation of the reaction

Answer 21

30 degrees Celsius, aqueous solution of the glucose, absence of air, yeast added;

Question 22

What are carboxylic acids?

Answer 22

Organic compounds that contain a -COOH functional group.

Question 23

State characteristics of carboxylic acids

Answer 23

• Dissolve in water to form an acidic solution (contains H+ ions).
• React with metal carbonates to form carbon dioxide.
• React with alcohols with an acid catalyst to produce esters.
• React with metals to give off hydrogen gas.

Question 24

What type of acid is carboxylic acid?

Answer 24

It is a weak acid

Question 25

Explain why carboxylic acids are weak acids?

Answer 25

They are partially dissociated in water, thus the pH of a carboxylic acid in solution is not as low as a solution of a strong acid of the same concentration.

Question 26

What is an ester and how is it formed? What is characteristic about this class of compounds?

Answer 26

An organic compound containing a -COO- functional group, formed from carboxylic acid and alcohol in presence of a sulfuric acid catalyst.
Fruity smell.

Question 27

What is a polymer? How do molecules containing C=C bond form polymers?

Answer 27

A polymer is a long chain molecule which is made by lots of smaller molecules
joining together.
C=C bonds open up and many smaller molecules (monomers) join together to form a chain (a polymer). No other products are made.
It is called an “addition polymerisation” reaction.

Question 28

Give 3 examples of addition polymers and their uses

Answer 28

• Polyethene - plastic bags
• (Poly)tetrafluoroethene (PTFE) - teflon surfaces, for use in non-stick kitchenware
• (Poly)chloroethene (polyvinylchloride, PVC) - water pipes

Question 29

What is a repeating unit of a polymer?

Answer 29

It is a smallest structure which, upon numerous translations, yields the structure of the polymer.
In addition polymers: to draw it, take a monomer, change C=C to C-C and show additional single bonds extending away from these carbons.

Question 30

What is a condensation polymer? How is it made? There are 2 main groups - name them and give industrially relevant examples

Answer 30

It is a polymer made in condensation polymerisation.In this reaction, many molecules join together; the polymer is formed, but also a small molecule is released, e.g. H2O, HCl.
Polyesters, e.g. terylene.
Polyamides, e.g. Nylon.

Question 31

What is the arrangement of C-H bonds in methane?

Answer 31

Tetrahedral

Question 32

Why are alkanes considered unreactive?

Answer 32

They exclusively contain relatively strong C-C and C-H bonds; these are quite difficult to break.

Question 33

Alkanes can undergo halogenation reactions.
Describe this process.

Answer 33

The reaction involves substituting hydrogen atoms with halogen atoms in the
alkane molecule.
It requires UV radiation. This radiation breaks up the halogen molecules into free
atoms (e.g. Cl2 becomes 2 Cl).

Question 34

How can ethanol be oxidised? What are the products?

Answer 34

Question 35

Name the ester made from the acid catalysed esterification of CH₃CH₂CH₂COOH and CH₃OH

Answer 35

Butanoic acid and methanol will form methyl butanoate and water

Question 36

What are isomers? How many isomers of C₅H₁₂ are there?

Answer 36

Isomers are compounds of the same molecular formula having different structural
formulae.
Three - try to draw them; if you can’t, google “isomers of C₅H₁₂”

Question 37

Addition polymerisation requires an additive - what’s its name and role?

Answer 37

An initiator.
It’s a chemical that initiates the addition polymerisation by helping one of the C=C bonds to break.

Question 38

What are biopolyesters?

Answer 38

These are a special type of polyesters that degrade upon prolonged exposure to microbes, O₂ and water (contrary to normal polyesters, which are resistant to decomposition under these conditions).