Hydrocarbons

Question 1

What is crude oil?

Answer 1

Crude oil is a mixture of compounds; a fossil fuel consisting of the remains of ancient biomass mainly of plankton that was buried in mud.
Most of the compounds in crude oil are hydrocarbons,
Finite resource - cannot be replaced as it is used up.

Question 2

What is a hydrocarbon?

Answer 2

A compound made up exclusively of hydrogen and carbon atoms

Question 3

What are alkanes?

Answer 3

Saturated hydrocarbons of a general formula 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 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 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

What are the conditions for cracking?
cracking is a thermal decomposition reaction-breaking down molecules by heating them.
Heat long chains of hydrocarbons to vaporise them.
Then the vapor can be passed over a hot powdered aluminium oxide catalyst.
The long chain molecules split apart on the surface of the specks of a catalyst-catalyst cracking.
Crack hydrocarbons if you vaporise them, mix them with steam and heat them to a very high temperature- Steam cracking

Question 11

How are the products of cracking used?

Answer 11

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

Question 12

What is an alkene?

Answer 12

What is an alkene?
Unsaturated hydrocarbon. Contains a C=C bond.
General formula for alkenes 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 reactions of alkenes

Answer 15

Addition atoms across the carbon-carbon double bond so that the double bond
becomes a single carbon-carbon 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 characteristics of methanol, ethanol, propanol and butanol

Answer 17

State characteristics of methanol, ethanol, propanol and butanol

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 18

Oxidation of the alcohols leads to…?

Answer 18

Carboxylic acids

Question 19

What are some uses of
alcohols?

Answer 19

Fuels
Solvents
Drinks

Question 20

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

Answer 20

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

C6H12O6 → 2 CH3CH2OH + 2 CO2

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 off 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 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 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 acid 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

Answer 26

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 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 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 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 molecule is released, e.g. H2O, HCl.
Polyesters, e.g. terylene.
Polyamides, e.g. Nylon.

Question 30

What is an amide bond?

Answer 30

An amide bond is similar to the ester bond, with O replaced by N, e.g.
(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 functionality
(COOH) and an amine functional group (-NH2).

Question 32

How do amino acids make
proteins? What are
polypeptides?

Answer 32

By numerous condensation polymerisation reactions; 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 proteins as a product of many
polypeptide chains bonded together.

Question 33

What are carbohydrates?

Answer 33

They are organic molecules made of C,H, and O. They are biologically relevant,
e.g. 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 two polymer chains that are held together in a double helix.
Each polymer chain can be made from 4 different monomers - nucleotides.