Homologous Series

Question 1

Explain what is meant by a homologous series.

Answer 1

A family of compounds with the same general formula and similar chemical properties.

Question 2

What happens to the boiling points of a homologous series as the size of the molecule increases?
Why does this happen?

Answer 2

The boiling points increase.

The larger the molecule, the stronger the intermolecular forces are. These forces need to be broken for the compound to be boiled, so the stronger the forces, the greater the boiling point.

Question 3

Define “hydrocarbon”.

Answer 3

A compound containing hydrogen and carbon only.

Question 4

What does it mean if a compound is saturated?

Answer 4

The compound contains only single carbon-carbon bonds.

Question 5

What does it mean if a compound is unsaturated?

Answer 5

The compound contains at least one double carbon-carbon bond.

Question 6

Give a chemical test, including the result, that allows identification of unsaturated molecules.

Answer 6

Adding bromine solution to an unsaturated compound will turn the bromine from brown to colourless.

In the presence of a saturated compound, bromine remains brown.

Question 7

What are the differences between general formulae, molecular formulae, shortened structural formulae and full structural formulae?

Answer 7

A general formula is a generic formula for all compounds in a homologous series.

A molecular formula is the number of each kind of atom in a compound.

A shortened structural formula groups the compound by carbon atoms, showing no bonds except C=C bonds.

A full structural formula shows all bonds and atoms in the correct positions.

Question 8

Explain what is meant by an isomer.

Answer 8

A compound with the same molecular formula but different structural formula.

Question 9

True or False:

1. Isomers must belong to the same homologous series.
2. Isomers have similar physical properties.

Answer 9

Both false.

Isomers do not have to belong to the same homologous series, and usually have different physical properties.

Question 10

Give a use of the alkanes.

Answer 10

Fuels.

Question 11

State whether the alkanes are soluble in water or not.

Answer 11

Insoluble.

Question 12

What is the general formula for the alkanes?

Answer 12

C(n)H(2n+2)

Question 13

State whether the alkanes are saturated or unsaturated hydrocarbons.

Answer 13

Saturated.

Question 14

Name the first eight straight-chain alkane in order of number of carbons.

Answer 14

Methane, ethane, propane, butane, pentane, hexane, heptane, octane.

Question 15

Give two uses of the cycloalkanes.

Answer 15

Fuels and solvents.

Question 16

State whether the cycloalkanes are soluble or insoluble.

Answer 16

Insoluble.

Question 17

What is the general formula for the cycloalkanes?

Answer 17

C(n)H(2n)

Question 18

Name the first six cycloalkanes.

Answer 18

Cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane.

Question 19

State whether the cycloalkanes are saturated or unsaturated.

Answer 19

Saturated.

Question 20

Give two uses of alkenes.

Answer 20

Fuels and solvents.

Question 21

State whether alkenes are soluble or insoluble.

Answer 21

Insoluble.

Question 22

State whether alkenes are saturated or unsaturated hydrocarbons.

Answer 22

Unsaturated.

Question 23

What is the general formula for the alkenes?

Answer 23

C(n)H(2n)

Question 24

State the functional group present in alkenes.

Answer 24

C=C double bond.

Question 25

Name the first 7 alkenes.

Answer 25

Ethene, propene, butene, pentene, hexene, heptene, octene.