chapter 15- Alcohols

Question 1

what is the suffix/prefix given to the -OH functional group

Answer 1

suffix= -ol
prefix= hydroxy-

Question 2

what is the C-O-H angle in an alcohol and its shape

Answer 2

104.5 degrees/ 105 degrees
bent (based off tetrahedral)

Question 3

what is a primary, secondary and tertiary alcohol

Answer 3

primary- an alcohol where only one R group is bonded to the carbon of the -OH functional group
secondary- an alcohol where two R groups are bonded to the carbon of the -OH functional group
tertiary- an alcohol where three R groups are bonded to the carbon of the -OH functional group

Question 4

why do alcohols have higher melting and boiling points than alkanes of similar relative molecular mass

Answer 4

because the -OH groups in alcohols means that hydrogen bonding occurs which raises the m.p and b.p

Question 5

how is ethanol made industrially

Answer 5

-by reacting ethane (made from cracking crude oil) with steam, using a catalyst of phosphoric acid

• from sugars by fermentation

Question 6

how is ethanol made from fermentation

Answer 6

during fermentation, carbohydrates from plants are broken down into sugars by a process called anaerobic respiration and then converted into ethanol by the action of enzymes from yeast

Question 7

why is ethanol made by fermentation known as carbon neutral

Answer 7

because the CO2 released when it is burned is balanced by the CO2 absorbed by the plant from which it was originally obtained

Question 8

what is carbon neutral

Answer 8

no net release of carbon dioxide into the atmosphere

Question 9

equation showing carbon neutrality in ethanol made by fermentation

Answer 9

6 CO2 + 6 H2O ———- C6 H12 O6 + 6 CO2
C6 H12 O6 ———- 2 C2 H5 OH + 2 CO2
2 C2 H5 OH + 6O2 ———- 4 CO2 + 6 H2O

6 CO2 absorbed = 6 CO2 released

Question 10

what do alcohols produce in complete combustion

Answer 10

carbon dioxide and water

Question 11

what is a use of ethanol

Answer 11

a fuel

Question 12

what is the molecule that leaves alcohols in an elimination reaction

Answer 12

water

Question 13

how are alcohols dehydrated and what do they form

Answer 13

• dehydrated with excess hot concentrated sulfuric acid
• or by passing their vapours over heated (600k) aluminium oxide

forms an alkene

Question 14

what are primary alcohols oxidised to

Answer 14

aldehydes (can be further oxidised into carboxylic acids)

Question 15

what are secondary alcohols oxidised into

Answer 15

ketones (cannot be oxidised further)

Question 16

why can’t tertiary alcohols and ketones be easily oxidised

Answer 16

because potassium dichromate is not strong enough to break the C-C bonds found in tertiary alcohols

Question 17

in an oxidation reaction using potassium dichromate what are the dichromate ions reduced to

Answer 17

orange dichromate ions ——— green chromium ions

Question 18

how do you oxidise ethanol (primary alcohol) to ethanal (an aldehyde)

Answer 18

• you use dilute acid and less potassium dichromate than that is needed for complete oxidation into a carboxylic acid
• you heat the mixture gently using a distillation apparatus
• the receiver of the condensed products is cooled in ice to reduce evaporation of the product
• the ethanal (b.p 294k) vaporizes as soon as it is formed and distils off
• this stops it further from being oxidised further to ethanoic acid
• unreacted ethanol remains in the flask

Question 19

what is the reaction equation of ethanol being oxidised to ethanal

Answer 19

CH3 CH2 OH (l) + [O] ——- CH3 CHO (g) + H2O (l)

Question 20

how do you oxidise ethanol (primary alcohol) to ethanoic acid (a carboxylic acid)

Answer 20

• you use concentrated sulfuric acid and excess potassium dichromate
• the mixture is refluxed by the reflux condenser
• whilst the reaction mixture is refluxing, any ethanol or ethanal vapour will condense and drip back into the flask until eventually it is all oxidised to the acid
• after around 20 minutes, you can distil off the ethanoic acid (b.p 391k) along with any water by changing the apparatus to a normal distillation one.

Question 21

what is the reaction equation for the oxidation of ethanol to ethanoic acid

Answer 21

CH3 CH2 OH (l) + 2[O] ——— CH3 COOH (g) + H2O (l)

Question 22

what is the Tollens’ Test and how is it done

Answer 22

a test for aldehydes and ketones

• tollens reagent oxidises aldehydes but has no effect on ketones
  -it contains colourless silver complex ions, containing Ag+, which are reduced to metallic silver Ag as the aldehyde is oxidised
• on warming an aldehyde with tollens reagents a deposit of metallic silver is formed on the inside of the test tube

Question 23

how do you make tollens reagent

Answer 23

a solution of silver nitrate mixed with aqueous sodium hydroxide. aqueous ammonia is added dropwise until the precipitated silver oxide completely dissolves

Question 24

what is the Fehlings’ test and how do you do it

Answer 24

a test for aldehydes or ketones

-fehlings reagent contains clue copper complex ions which will oxidise aldehydes but not ketones
- you warm the soloution with the blue fehlings soloution. if an aldehyde the solution will form a brick red precipitate