7.4 Alcohols Flashcards
How can alcohols be produced and what are their properties?
general formula
CnH(2n+1) OH
primary vs secondary vs tertiary alcohols
depends on number of carbons connected to terminal carbon
boiling point of primary -> tertiary alcohols increase/decrease? why?
DECREASES because more branching = less surface area = less forces of attraction = higher BP
at what point do alcohols become
(1) visibly insoluble
(2) completely insoluble
(1) 1-pentanol (C5)
(2) 1-octanol (C8)
complete combustion of alcohol equation
alcohol + excess oxygen
alcohol + O2 –> CO2 + H2O
incomplete combustion of alcohol equation
alcohol + O2 –> CO(g) + C(s) + H2O
*C + H2O = soot
(enthalpy of combustion prac) why is experimental value is much lower than published value? (4)
(1) heat loss to surroundings +
(2) heat absorbed by equipment,
(3) incomplete combustion (air = not in pure oxygen),
(4) evaporation of alcohol from spirit burner wick since alcohol has low BP
heat released per litre of fuel =
ΔH/MM x fuel density (g L⁻)
process to produce alcohol in beverages and biofuels =
fermentation
process to produce industrial alcohol = (2)
hydration of alkenes
OR substitution of haloalkenes
dehydration of alcohol process
alcohol –> alkene + H2O
using concentrated acid or alumina (Al2O3) catalyst
hydrohalogenation process
alcohol + HX –> alkyl halide + H2O
HX = hydro halides e.g. HBr, HI, HCl
alcohol reactivity order in hydrohalogenation process
°3 > °2 > °1
oxidation of primary alcohol
alkane + primary alcohol –> aldehyde + carboxylic acid
oxid. of secondary alcohol
alkane + secondary alc –> ketone
what type of reaction, and what catalyst?:
haloalkane + OH⁻ –> alcohol + halogen
substitution…
base catalyst e.g. NaOH
common reagent for oxid. of secondary alcohols
chromic acid H2CrO4
oxid. of tertiary alcohol
alkane <–> tertiary alc (no oxidation)
hydration/hydrolysis of alcohols
alkene + H2O –> alcohol
*catalyst dilute H2SO4 or H3PO4
two opposing solubility trends in alcohols
(1) polar -OH promotes solubility in water by forming H bonds
(2) NP hydrocarbon chain resisting solubility in water
why ethanol is renewable
can be produced from re-growable plants AND manufactured from carbohydrates
(2) pros using ethanol
(1) renewable, reduces greenhouse gas
(2) burns more completely = less pollutants
(2) cons using ethanol
(1) large agricultural land devoted to growing suitable crops for ethanol
(2) problem disposing fermentation waste
explain fermentation of alcohol
glucose breaks down into ethanol and CO2 by enzymatic action in yeast
ingredients for fermentation
plant matter + yeast
conditions for successful fermentation of ethanol (4)
(1) around 37deg
(2) anaerobic (no oxygen)
(3) pH 6.1 - 6.8
(4) dilute mixture maintained below 14% ethanol (w/v)
step to remove ethanol from yeast mixture after fermentation
fractional distillation based on ethanol BP at 78deg
what is molar heat of combustion
heat energy released in complete combustion reaction of 1 mol of a substance
how to test 1deg and 2deg
2,4-DNPH
use 2,4-Dinitrophenylhydrazine
1deg changes colour
how to test for 3deg
add acidifed Cr2O7 (2-) dichromate with H2SO4
reduces to Cr 3+ (green)
3deg does not turn green, stays orange
what is reflux
heating the chemical reaction for a specific amount of time, while continually cooling the vapour produced back into liquid form, using a condenser
easily oxidised alcohol is when
C in functional group is directly connected to H
