Organic 4 Alcohols

Question 1

Solubility decreases with increased chain length….

Answer 1

Because as the non polar section/ carbon chain length increases, the hydroxyl group becomes less significant

Question 2

Aldehyde

Answer 2

C=O at end of molecule

Question 3

Ketone

Answer 3

C=O in middle of molecule

Question 4

Oxidation

Answer 4

Removal of hydrogen
Addition of oxygen

Question 5

Acidified potassium manganate (Vl) [O]

Answer 5

Heated with alcohol, alcohol oxidises the solution
Purple to colourless

Question 6

Acidified potassium dichromate [O] + H2SO4

Answer 6

Orange to green
H+/K2Cr2O7
Weaker oxidising agent so is used for oxidising primary alcohols to aldehydes then stopping there

Question 7

Fehlings solution

Answer 7

Blue to red
Presence of aldehyde
(Copper (ll) ions dissolved jn NaOH)

Question 8

Benedict’s solution

Answer 8

Blue to brick red precipitate
Copper ll ions dissolved in Na2CO3
Reduced to copper l oxide

Question 9

Primary alcohol to aldehyde

Answer 9

Heat alcohol in excess with [O]
Aldehyde evaporates into condensing chamber and distilled off immediately

Question 10

Primary alcohol to carboxylic acid

Answer 10

Excess [O]
Heat under reflux

Question 11

Secondary alcohol to ketone

Answer 11

Reflux with acidified potassium dichromate

Question 12

Alcohol ➡️alkene
Reagent
Type of reaction

Answer 12

Concentrated phosphoric acid
Elimination, dehydration
Heat
Hydrogen ions act as catalyst (released by the acids)

Question 13

Alcohol ➡️alkene mechanism description (not required to learn)

Answer 13

Hydrogen ion accord lone pair on oxygen, bonds to it
Molecule now electron deficient so C-O bond breaks by Heterolytic fission releasing H2O
Carbocation makes molecule unstable
C-H bond breaks by Heterolytic fission and the electrons migrate forming a C=C
Releases a H+ so a H+ has been regenerated hence it’s a catalyst

Question 14

Test for carboxylic acids

Answer 14

Add sodium carbonate
Effervescence due to release of CO2 (neutralisation)

Question 15

Alcohol ➡️chloroalkane
Reagent
Type and mechanism

Answer 15

PCl5
Nucleophilic substitution
Produces choroalkane, phosphorus chlorate (POCl3) and HCl (whispy fumes)

Question 16

Alcohol ➡️bromoalkane
Reagent

Answer 16

HBr produced in situ
Alcohol mixed with potassium bromide and 50% concentrated sulfuric acid to produce HBr and K2SO4
Reflux then distil to separate
OH replaced by bromide

Question 17

Alcohol ➡️iodoalkane

Answer 17

Phosphorous tri iodide (PI3) produced in situ
Red phosphorus and iodine reacted together
Reflux then distil
Produces H3PO3 too

Question 18

Why does melting and boiling temperature increase with increased chain length

Answer 18

Stronger London (induced dipole) forces

Question 19

Drawbacks of biofuels (bio ethanol)

Answer 19

Not carbon neutral due to manufacture (fertilisers), transport and powering agricultural machinery
Fermentation is a slow, batch process so may not meet fuel/electricity demands
Land used for these crops will take land away from food production
Less energy released compared to traditional alkane fuels- cars will be less efficient