Properties of Hydrocrabons

Question 1

General Properties (Intermolecular Forces and Polarity)

Answer 1

• Hydrocarbons have weak dispersion forces
• are non-polar (C-C bonds are NON polar, C-H bonds are slightly polar)
• Overall symmetry of alkane molecule means there is no net dipole therefore alkanes are non polar

Question 2

Boiling point/Melting Point

Answer 2

• Increases with with increase chain length due to more dispersion forces
• As molecules become longer, “net” dispersion forces become stronger
• Straight chain alkanes stack together more closely therefore have strong dispersion forces and higher BP/MP
• Haloalkanes have higher BP/MP than normal alkanes.
• Haloalkanes contain bonds that are polar, these stronger dipole-dipole attractions between halogen and carbon + disperson forces means higher BP/MP

Question 3

Solubility of Hydrocarbons

Answer 3

(LIKE DISSOLVES LIKE)
Hydrocarbons are NON POLAR so therefore:
-Unsoluable in Polar Molecules e.g.
-Soluble in Non-Polar Molecules e.g. Organic Solvents

Weak dispersion forces between the water molecules and the hydrocarbons are not strong enough to overcome the strong attraction between water molecules therefore they don’t mix

Soulble in organic solvents that contain alkanes or symmetrical haloalkanes because the force of attraction between molecules of these liquids are also weak dispersion forces and are similar in strength to the alkane-alkane forces of attraction

-Haloalkanes are slightly more soluble in water due to polar halogen-carbon bonds,
-the influence of the halogen decreases as the length of the C chain increase (as net forces become non polar)
- Haloalkanes are denser so form layer on bottom
when added to water

Question 4

Safety (Volatility)

Answer 4

• Shorter chain length = more volatile due to weak dispersion forces
• High volatility = high risk that hydocarbon turns into a vapour and combust

Question 5

How are Hydrocarbons stored / Disposed?

Answer 5

• Stored in Gas Bottles
• Odours added to enable detection by smell
• Warning signs and labels

Disposed:

• Stored in light-dispersive glassware and collected by agencies
• Collected and left to vaporise under controlled conditions