module 4.2: alcohols, haloalkanes, organic synthesis and analysis techniques

Question 1

what is the functional group of an alcohol?

Answer 1

hydroxyl

Question 2

how do you name an alcohol with more than one hydroxyl group?

Answer 2

-diol
ex. butane-diol

Question 3

uses of methanol and ethanol:

Answer 3

methanol: used in combustion as high performance fuel, it is also used in chemical feedstock (as the starting material in many industrial syntheses
ethanol: used in alcoholic drinks, fuel,, solvents and as a feedstock

Question 4

steps to name an alcohol:

Answer 4

1) identify parent chain
2) see the positioning of the -OH groups
3) identify any side groups
4) order according to alphabetical order

Question 5

Why are alcohols more water soluble than alkanes?

Answer 5

-the polar O-H groups can form hydrogen bonds with the water molecules
-this increases the solubility in water
-alkanes are non-polar and can therefore not make hydrogen bonds with water
-the influence of the -OH group diminishes as you increase the length of the chain and the solubility of the alcohols decrease the longer the carbon chain is

Question 6

Why do alcohols have lower volatility and higher boiling points than alkanes?

Answer 6

• the O-H bond in alcohols are more polar (due to the difference in electronegativity between oxygen and hydrogen) than C-H bonds in alkanes (which are considered non-polar because there is little difference in the electronegativity between C and H)
• stronger hydrogen bonds can form between the polar O-H groups which are stronger than the weak intermolecular forces formed between C-H groups (non-polar molecules)
• more energy is required to break the stronger hydrogen bonding making it harder to change the state from liquid to gas, making it less volatile

Question 7

What are the physical properties of alcohols?
(especially when compared to alkanes of the same carbon chain length)

Answer 7

-less volatile
-higher melting point
-greater water solubility

Question 8

What is a primary alcohol?
Secondary?
Tertiary?

Answer 8

-the -OH group is attached to a carbon that is attached to 1 ALKYL GROUP and two hydrogen atoms
-the -OH group is attached to a carbon that is attached to 2 ALKYL GROUPs and one hydrogen atom
-the -OH group is attached to a carbon that is attached to 3 ALKYL GROUPs and no hydrogen atoms

Question 9

Combustion of Alcohols

Answer 9

-alcohols undergo complete combustion to produce CO2 and water
-it is an exothermic reaction (with the energy being released as heat)
-the quantity of heat released increases as the length of carbon chains increase