chapter 15- Alcohols Flashcards
(25 cards)
what is the suffix/prefix given to the -OH functional group
suffix= -ol
prefix= hydroxy-
what is the C-O-H angle in an alcohol and its shape
104.5 degrees/ 105 degrees
bent (based off tetrahedral)
what is a primary, secondary and tertiary alcohol
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
why do alcohols have higher melting and boiling points than alkanes of similar relative molecular mass
because the -OH groups in alcohols means that hydrogen bonding occurs which raises the m.p and b.p
how is ethanol made industrially
-by reacting ethane (made from cracking crude oil) with steam, using a catalyst of phosphoric acid
- from sugars by fermentation
how is ethanol made from fermentation
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
why is ethanol made by fermentation known as carbon neutral
because the CO2 released when it is burned is balanced by the CO2 absorbed by the plant from which it was originally obtained
what is carbon neutral
no net release of carbon dioxide into the atmosphere
equation showing carbon neutrality in ethanol made by fermentation
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
what do alcohols produce in complete combustion
carbon dioxide and water
what is a use of ethanol
a fuel
what is the molecule that leaves alcohols in an elimination reaction
water
how are alcohols dehydrated and what do they form
- dehydrated with excess hot concentrated sulfuric acid
- or by passing their vapours over heated (600k) aluminium oxide
forms an alkene
what are primary alcohols oxidised to
aldehydes (can be further oxidised into carboxylic acids)
what are secondary alcohols oxidised into
ketones (cannot be oxidised further)
why can’t tertiary alcohols and ketones be easily oxidised
because potassium dichromate is not strong enough to break the C-C bonds found in tertiary alcohols
in an oxidation reaction using potassium dichromate what are the dichromate ions reduced to
orange dichromate ions ——— green chromium ions
how do you oxidise ethanol (primary alcohol) to ethanal (an aldehyde)
- 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
what is the reaction equation of ethanol being oxidised to ethanal
CH3 CH2 OH (l) + [O] ——- CH3 CHO (g) + H2O (l)
how do you oxidise ethanol (primary alcohol) to ethanoic acid (a carboxylic acid)
- 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.
what is the reaction equation for the oxidation of ethanol to ethanoic acid
CH3 CH2 OH (l) + 2[O] ——— CH3 COOH (g) + H2O (l)
what is the Tollens’ Test and how is it done
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
how do you make tollens reagent
a solution of silver nitrate mixed with aqueous sodium hydroxide. aqueous ammonia is added dropwise until the precipitated silver oxide completely dissolves
what is the Fehlings’ test and how do you do it
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
