why are alcohols less volatile and have higher melting point than alkanes
- polar -OH on the alcohol can form much stronger H bonds with other -OH groups, on top of the weak London forces present in alkanes
- more energy needed to overcome these bonds
why are alcohols more soluble in water than alkanes
- the polar -OH group of alcohol molecules, not present in alkanes, can H bond with water
what makes the -OH group polar
- electronegativity of O allows it to attract bonding electrons more than H, giving the H a slightly +ve charge
why does solubility of alcohols decrease with increase in size
- in larger alcohols, most of the molecule is a non-polar C chain so there’s less attraction for the polar H2O molecules
what kind of combustion do alcohols undergo and what does it form
- complete combustion
- exothermic reaction
- produces water and carbon dioxide
what reagents is used to oxidise alcohols
- K2Cr2O7/ H2SO4
- Cr2O7^2-/ H+
Which type of alcohols can’t be oxidised and what would be the observation
3*
- solution remains orange
reaction conditions, general equation and observation of oxidation of 1* alcohol to aldehyde
- dilute acid, gentle heating, distillation
- 1* alcohol + [O] –(CrO7^2-/ H+)–> aldehyde + water
- colour change from orange to green
reaction conditions, general equation and observation of oxidation of 1* alcohol to carboxylic acid
- conc acid, vigorous heating, reflux
- 1* alcohol + 2[O] –(CrO7^2-/ H+)–> carboxylic acid + water
- colour change from orange to green
- ONLY OXIDATION THAT NEEDS 2[O]
reaction conditions, general equation and observation of oxidation of 2* alcohol to ketone
- conc acid, vigorous heating, reflux
- 2* alcohol + [O] –(CrO7^2-/ H+)–> ketone + water
- colour change from orange to green
reaction conditions, general equation and observation of oxidation of aldehydes to carboxylic acids
- dilute acid, vigorous heating, reflux
- aldehyde + [O] –(CrO7^2-/ H+)–> carboxylic acid
what are elimination reactions
when molecule loses atoms, forming a C=C
general equation for the elimination of alcohols to form alkenes
alcohol –(conc H2SO4 and heat under reflux)–> alkene + H2O
- there are often 2 possible alkene products from one elimination reaction depending on which side of the -OH group the H is eliminated from
- E/Z isomerism may arise from this
elimination of alcohols to form alkenes is also an example of which type of reaction
dehydration
general formula for alcohols
CnH(2n+2)O
