Alcohols Flashcards
what is the properties of alcohols?
they are less volatile, have high melting points, and greater water solubility
why do alcohols have higher boiling points than alkanes
alcohols have a polar 0-H bond because of the difference in electronegativity, therefore, are polar and form hydrogen bonds.
why do alcohols have low volatility?
in liquid form , alcohols gave hydrogen bonds which requires more energy to overcome
why are alcohol soluble in water>
they have polar 0H- group
what happens when hydrocarbon chain of alcohol increase?
influence of OH group becomes relatively smaller so solubility decrease
why does spraying ethylene glycol (ethane-1,2 diol) at ice help the ice to melt?
water freezes at 0 degrees but when ethylene glycol is added which has a freezing point of -13 degrees, it makes the mixture have a freezing point of -40 degree.
what is a primary alcohol
an OH group attached to a carbon which is attached to 2 hydrogen atoms and an alkyl group
what is a secondary alcohol
an OH group attached to a carbon atom which is attached to one hydrogen atom and 2 alkyl groups
what is a tertiary alcohol
an OH group attached to a carbon atom which is attached to no hydrogen atoms and 3 alkyl groups
is the combustion of alcohol exothermic or endothermic?
exothermic
what is the product for oxidation of primary alcohols?
aldehydes or carboxylic acids
what is used for oxidation of primary alcohols?
potassium dichromate , K2Cr2O7 , acidified with dilute sulfuric acid
what happens to orange solution contain dichromate ions, Cr2O7^-2 , when primary alcohol is oxidised
solution changes from orange to green as dichromate ions are reduced to chromium ion, Cr^3+
what is aldehyde prepared?
primary alcohol gently heated with acidified potassium dichromate
how is it ensured that an aldehyde is formed rather than a carboxylic acid
aldehyde is distilled out of the reaction mixture as it forms to prevent further reaction with oxidising agent.
how is carboxylic acid formed?
primary alcohol is heated strongly under reflux with excess of acidified potassium dichromate.
what is the product for oxidation of secondary alcohols
secondary alcohols are oxidised to ketone under reflux
can tertiary alcohols undergo oxidation reactions?
no
how is an alcohol dehydrated?
alcohol is heated under reflux in presence of acid catalyst to form an alkene, removing h20
what happens when alcohol reacts with hydrogen halide
forms haloalkane under reflux with sulfuric acid and a sodium halide which forms hydrogen bromide in situ
NaBr + H2SO4 —— NaHSO4 + HBR
the hydrogen bromide reacts with alcohol to form haloalkane
what is the overall equation for the substitution reaction of alcohol with hydrogen halide to form haloalkane
NaBr + H2SO4 + CH3CHOHCH3 —— CH3CHBRCH3 + NAHSO4+ H20
