Chapter 14.1 - Properties of alcohols Flashcards
What is the functional group of alcohols?
-OH
Give a use for methanol
Fuel - efficient combustion
Give two uses for ethanol
- In alcoholic drinks
- Solvent
What is the general formula of alcohols?
CₙH₂ₙ₊₁OH
What is the molecular formula of alcohols?
CₙH₂ₙO
Give three differences between alkanes and alcohols
1) Alcohols are less volatile
2) Alcohols have higher melting points
3) They have a greater water solubility than the corresponding alkane
What is meant by votality?
How easily a substance will vaporise
Describe why alkanes are non polar molecules and the london forces
- The electronegativity of hydrogen and carbon are very similar
- So the molecules are therefore non polar
- The intermolecular forces between the non polar molecules are weak london forces
Describe why alcohol are polar molecules and the london forces
- The electronegativity of hydrogen and oxygen is greatly different
- So the molecules are therefore polar
- The intermolecular forces between the polar molecules will be weak london forces as well as much stronger hydrogen bonds between the polar O-H groups
Draw the hydrogen bond between two ethanol molecules
:)
Explain the low votality of alcohols compared to alkanes, referring to high boiling points
- In liquid states, intermolecular hydrogen bonds between the O-H groups hold the alcohol molecules together
- These bonds must be broken in order for the liquid alcohol to change into a gas
- This requires much more energy than overcoming the weak london forces in alkanes
- So alcohols have a lower votality than alkanes with the same number of carbon chains
Why are the first four alcohols soluble in water?
- This is because hydrogen bonds form between the polar OH group of the alcohol and the water molecules
- Furthermore, a compound that can form hydrogen bonds with water is far more water soluble than a compound that cannot
Why does the solubility of alcohols decrease as the hydrocarbon chain increases in size?
- The influence of the OH group becomes relatively smaller
- Therefore the solubility decreases
Explain how de-icers work
- Water freezes at 0°C
- Ethane-1,2-diol at 13°C
- When they are mixed together, the freezing point can be as low as -40°C
- Causing the mixture to melt
What are the three classifications of alcohols?
1) Primary - one alkyl group + two hydrogens
2) Secondary - two alkyl groups + one hydrogen
3) Tertiary - three alkyl groups + no hydrogens
