Hydrocarbons, and other functional groups

Question 1

What is a functional group?

Answer 1

Specific groups of atoms within molecules that are responsible for characteristic chemical reactions.

Question 2

What are hydrocarbons, alkanes and alkenes?

Answer 2

1. Hydrocarbons are compounds composed of only hydrogen and carbon atoms.
2. An alkane is a saturated hydrocarbon in which all the carbon-carbon bonds are single.
3. An alkene is an unsaturated hydrocarbon containing a double bond.

Question 3

Give 2 properties of hydrocarbons.

Answer 3

1. The shorter the carbon chain:
   
   • the less viscous it is
   • the more flammable it is
   • the more volatile it is
   • the lighter it is in colour
   • the lower its boiling point
2. Hydrocarbon + oxygen = carbon dioxide + water + energy
   
   • Hydrocarbons/ carbon-based compounds are used as fuels because of how much energy is released when they combust fully.

Question 4

Give 2 properties of alkanes.

Answer 4

1. Atoms in alkanes are held together by single covalent bonds.
2. In substitution reactions, a hydrogen atom is replaced by a halogen.
   
   • i.e Methane + Bromine = Methylbromine + Hydrogen bromide

Question 5

Give 3 properties of alkenes.

Answer 5

1. Very flammable
2. In the complete combustion of an alkene, carbon dioxide and water are formed.
   
   • alkene + oxygen = carbon dioxide + water
3. In the incomplete combustion of an alkene, carbon monoxide, carbon and water are formed.
   
   • alkene + oxygen = carbon monoxide + carbon + water

Question 6

How do we test for alkenes?

Answer 6

Shake the substance with bromine water to see if an addition reaction takes place.

• If the substance is an alkene, the solution will turn colourless (decolourised)
• i.e Ethene + Bromine = Dibromoethane

Question 7

Give the properties of alcohols.

Answer 7

Recognised by -OH (hydroxyl) functional group.

- i.e MethanOL is CH3OH, Propanol is CH3(CH2)2OH

Question 8

Give 2 properties of carboxylic acids.

Answer 8

1. Recognised by -COOH (carboxyl) functional group.
   
   • Methanoic acid is HCOOH or CH2O2
2. Contains a carbon to oxygen double bond.