A-LEVEL CHEMISTRY: 3.3.5: Alcohols (ChemRevise) Flashcards
if the compound has an -OH group in addition to other functional groups that need a suffix ending then the OH can be named with the prefix…
hydroxy-
if there are 2 or more -OH groups, then…
di, tri, are used
alcohols have relatively ___ volatility and ___ bp. why?
low, high.
due to their ability to form hydrogen bond between alcohol molecules
smaller alcohols can ___ in water. why?
dissolve. because they can form hydrogen bonds to water molecules
primary alcohols:
primary alcohols are alcohols where 1 carbon is attached to the carbon adjoining the oxygen
secondary alcohols:
secondary alcohols are alcohols where 2 carbons are attached to the carbon adjoining the oxygen
tertiary alcohols:
tertiary alcohols are alcohols where 3 carbon are attached to the carbon adjoining the oxygen
Potassium dichromate, ___, is an ___ ___ that causes ___ to ___.
K2Cr2O7, oxidising agent, alcohols, oxidise
explain partial oxidation of primary alcohols: (3)
-reaction: primary alcohol —> aldehyde
-reagent: potassium dichromate (VI) solution and dilute sulfuric acid
-conditions: warm, gently distil out the aldehyde as it forms
aldyhyde name ends in…
-al
explain full oxidation of primary alcohols: (3)
-reaction: primary alcohol —> carboxylic acid
-reagent: potassium dichromate (VI) solution and dilute sulfuric acid
-conditions: excess of potassium dichromate, heat under reflux
reflux:
reflux is used when heating organic reaction mixtures for specific periods of time, while continually cooling the vapour produced back into liquid form, using a condenser
when refluxing: (2)
-never seal the end of the container (due to build up of gas)
-anti-bumping granules (form small bubbles instead of large bubbles)
___ alcohols cannot be ___ at all by potassium dichromate. why?
tertiary, oxidised
because there is no hydrogen atom bonded to the carbon with the -OH group
explain oxidation of secondary alcohols: (3)
-reaction: secondary alcohol —> ketone
-reagent: potassium dichromate(VI) solution & dilute sulfuric acid
-conditions: heat under reflux
how to distinguish between aldehydes and ketones:
Tollens’ Reagent and Fehling’s Solution
test for the presence of carboxylic acid:
addition of sodium carbonate. it will fizz & produce carbon dioxide if present
explain reaction of alcohols with dehydrating agents: (4)
-reaction: alcohol —> alkene
-reagents: concentrated sulfuric or phosphoric acids
-conditions: warm (under reflux)
-role of reagent: dehydrating agent/catalyst
-type of reaction: acid catalysed elimination
dehydration reaction:
removal of a water molecule from a molecule
2 methods for forming ethanol: (2)
-fermentation
-industrial (from ethene)
word equation for formation of ethanol from fermentation:
glucose —> ethanol + carbon dioxide
symbol equation for formation of ethanol from fermentation:
C6H1206 —> 2CH3CH2OH + 2CO2
conditions needed for formation of ethanol from fermentation: (3)
-yeast
-no air
-temperatures (30’C - 40’C)
type of reaction of formation of ethanol from fermentation:
fermentation
optimum temperature for formation of ethanol from fermentation:
why?
~38’C
at lower temp., reaction is too slow
at higher temp., the yeast dies & the enzymes denature
fermentation is done in the absence of ___. why?
air.
because the presence of air can cause extra reactions to occur
advantages of formation of ethanol from fermentation: (2)
-sugar is a renewable resource
-production uses low level technology/cheap equipment
disadvantages of formation of ethanol from fermentation: (3)
-batch process (slow & high production costs)
-ethanol made needs to be purified by fractional distillation
-depletes land used for growing food crops
reagent for industrial formation of ethanol is…
where does it come from?
ethene
from cracking of fractions from distilled crude oil
type of reaction for industrial formation of ethanol?
hydration/addition
essential conditions for industrial formation of ethanol: (3)
-high temperature
-high pressure
-strong acidic catalyst H3PO4
advantages of industrial formation of ethanol: (3)
-faster reaction
-product formed is pure
-continuous process (cheaper manpower)
disadvantages of industrial formation of ethanol: (3)
-expensive equipment
-ethene is non-renewable (ethene is the reagent used)
-high energy costs (for high temp. & pressure)
biofuel:
a biofuel is a fuel produced from plants
carbon neutral:
an activity that has no net annual carbon emissions to the atmosphere
ethanol produced from fermentation is a ___.
biofuel
ethanol produced from ___ is a biofuel
fermentation
