Organic chemistry

Question 1

What is crude oil?

Answer 1

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

Question 2

What is a hydrocarbon?

Answer 2

A compound made exclusively of hydrogen and carbon atoms.

Question 3

What are alkanes?

Answer 3

Saturated hydrocarbons of a general formula of CₙH₂ₙ₊₂

Question 4

What is a homologous series?

Answer 4

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

Question 5

Describe the combustion of hydrocarbons

Answer 5

• Exothermic reactions occurring when hydrocarbons are reacted with oxygen.
• Complete combustion produce carbon dioxide and water (carbon and hydrogen atoms are completely oxidised).
• Incomplete combustion produces carbon monoxide and water (due to lack of oxygen).

Question 6

Describe the physical properties of alkanes

Answer 6

• 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 7

Explain how fractional distillation of crude oil takes place

Answer 7

• 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 8

What is cracking?

Answer 8

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

Question 9

What type of reaction is cracking?

Answer 9

Thermal decomposition.

Question 10

What are the conditions for cracking?

Answer 10

Catalytic cracking - reactant heated to vapour, passed over a hot catalyst.
Steam cracking - mixed with steam and heated to high temperatures.

Question 10

What are the conditions for cracking?

Answer 10

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

Question 11

How are the products of cracking used?

Answer 11

The products are alkanes and alkenes - alkenes are used as polymers and starting materials for synthesis of chemicals.

Question 12

What is an alkene?

Answer 12

Unsaturated hydrocarbon. Contains a C=C bond.

General formula is CₙH₂ₙ

Question 13

What is the test for alkenes?

Answer 13

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

Question 14

Describe the combustion of alkenes

Answer 14

They burn with smoky flames due to incomplete combustion.

Question 15

Describe addition reaction of alkenes

Answer 15

Addition atoms cross the C=C so that the double bond becomes a single C-C bond.

a) With hydrogen - hydrogenation; requires a higher temperature and a nickel catalyst.
b) With steam - hydration; requires high temperature, pressure and concentrated phosphoric acid (H₃PO₄) as a catalyst.
c) With Br₂/Cl₂/I₂ - addition of halogens.

Question 16

What is an alcohol?

Answer 16

An organic compound that contains an -OH functional group.

Question 17

State characteristic of methanol, ethanol, propanol and butanol

Answer 17

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

Question 18

Oxidation/Oxidising agent added of the alcohols lead to..?

Answer 18

Carboxylic acids.

Question 19

What are some uses of alcohol?

Answer 19

• Fuels.
• Drinks.
• Solvents.

Question 20

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

Answer 20

30°C, aqueous solution of the glucose, absence of oxygen yeast, added.

C₆H₁₂O₆ → 2CH₃CH₂OH + 2CO₂

Question 21

What are carboxylic acids?

Answer 21

Organic compounds that contain a COOH functional group.

Question 22

State characteristics of carboxylic acids

Answer 22

• 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 hydrogen gas.

Question 23

What type of acid is carboxylic acid?

Answer 23

It is a weak acid.

Question 24

Explain why carboxylic acids are weak acids

Answer 24

They are partially ionised in aqueous solution, 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 25

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

Answer 25

An organic compound containing a -COO- functional group, formed from carboxylic acids and alcohol in the presence of a sulfuric acid catalyst.
They have a fruity smell.

Question 26

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

Answer 26

A polymer is a long chain molecules, which is made by lots of repeating smaller molecules (monomers) 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 27

Give 3 examples of addition polymers and their uses

Answer 27

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

Question 28

What is a repeating unit of a polymer?

Answer 28

It is the smallest structure which, upon numerous translation, 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 29

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

Answer 29

It is a polymer made in condensation polymerisation.

In this reaction, many molecules join together; the polymer is formed, but also a small molecules is released such as H₂O, HCl.

• Polyesters: terylene.
• Polyamides: nylon.

Question 30

What is an amide bond?

Answer 30

An amide bond is similar to the ester bonds, with O replaced by N.
(C=O) - NH₂.
Just like an ester, it contains the C=O group.

Question 31

What is an amino acid?

Answer 31

It is an organic compound that contains both a carboxylic acid functional group (COOH) and an amine functional group (-NH₂-).

Question 32

How do amino acids make proteins? What are polypeptides?

Answer 32

By numerous condensation polymerisation reaction; proteins are polymers made of amino acids (monomers).

Polypeptides are also made by condensation polymerisation of amino acids, but are shorter than proteins. One could think about protein as a product of many polypeptide chains together.

Question 33

What are carbohydrates?

Answer 33

They are organic molecules made of C, H and O. They are biologically relevant - for starch and cellulose.
Both of these are polymers made of glucose (other carbohydrate) monomers. Their structures differ in the way the glucose molecules are joined together.

Question 34

What is DNA? Describe its role and structure

Answer 34

DNA (deoxyribonucleic acid) is a material that makes up chromosomes - cell structures that store genetic information.

DNA is made of 2 polymer chains that are held together in a double helix.

Each polymer chain can be made from 4 different monomers called nucleotides.