Alchohols

Question 1

General formula of alcohol

Answer 1

CnH2n+1OH

Question 2

What is a primary alcohol

Answer 2

The -OH group is attached to a carbon that has 1 other carbon attatched to it

Question 3

Secondary alcohol

Answer 3

The -OH group is attached to a carbon that has 2 other carbons attatched to it

Question 4

Tertiary alcohol

Answer 4

The -OH group is attached to a carbon that has 3 carbons attatched to it

Question 5

Are alcohols polar

Answer 5

Alcohols are generally polar molecules due to the the electronegative hydroxyl group which pulls the electrons in the C-OH bond away from the carbon atom

This means the electronegative oxygen draws electron density away from hydrogen , giving it a slightly positive charge - can attract lone pairs on an oxygen forming H bonds

Question 6

Alcohol + water - smaller vs larger alcohols

Answer 6

When you mix an alcohol with water, hydrogen bonds form between the oh- and h20

smaller - completely soluble

Larger - most of the molecule is non polar carbon chain, so there’s less attraction for the polar h20 molecules - less soluble in water

Question 7

Why do alcohols have low volatility ( don’t easily evaporate into a gas)

Answer 7

Alcohols form H bonding with EACH THER

HYdrogen bonding is the strongest type of intermolecular force, so it gives alcohols LOW volatility

Question 8

ALchohols vs alkanes

Answer 8

Alkanes have non polar bonds because electronegativity of C and H is too similar

Intermolecular forces = weak London forces

High volatility = low BP, not much energy required to break London dispersion
Non polar too- can’t form H bonds with each other

Question 9

Reactions of alcohols

Answer 9

Combustion
Oxidation
Dehydrating
Forming halo alkanes

Question 10

Combustion of alcohols

Answer 10

Burn completely in O2 (plentiful supply) to form h20 and co2
EXOTHERMIC reaction , releasing a lot of energy
As the number of C atoms in the chain increases, the au titis of heat released per mole also increases
C-C and C-H bonds broken

Question 11

Oxidation of primary alcohols

Answer 11

Partial oxidation
ALDEHYDE
Potassium dichromate solution+dilute sulphuric acid
Distil out aldehyde once formed

Question 12

Colour change ? Oxidation for primary alcohol.s

Answer 12

Dichromate changes colour from Orange to green ( Cr3+)

Question 13

Full oxidation of primary alcohols

Answer 13

CARBOXYLIC acid

Heat under reflux

Question 14

Secondary alcohol oxidation

Answer 14

Refluxing a secondary alcohol with acidified dichromate will reduce a KETONE and water

Again orange to green

alchohol + [o]—- ketone and water

Question 15

Tertiary alcohol oxidation

Answer 15

DO NOT react with dichromate - solution stays orange
Cannot be oxidised
No hydrogen atom bonded to carbon with OH group for the oxygen to remove

Question 16

Dehydrating alcohols

Answer 16

ALKENES
Eliminate H20
Eliminatin reaction
Alcohol mixed with acid catalyst e.g. H2so4, then heated
Water bonded to carbon atom adjacent to hyxxul carbon

Question 17

Halo alkanes from alcohols

Answer 17

HYDROGEN HALIDES 
Heat under reflux 
Sulphuric aci and halide ions 
Hydroxyl group replaced by halide 
Neucleophlic substitution