alcohols

Question 1

what are alcohols

Answer 1

a homologous series containing the hydroxyl (oh) group

Question 2

what are some commercially important alcohols

Answer 2

methanol , ethanol , ethane-1,2 diol

Question 3

how do we classify alcohols

Answer 3

alcohols are classified according to the enviroment of the OH group

Question 4

what are the 3 types of alcohols

Answer 4

primary, secondary or tertiary

Question 5

how do we classify primary , secondary and tertiary

Answer 5

classification depends on the number of R groups (alkyl) attached to the carbon carying the OH group

Question 6

why do alcohols have a lower than expected volatility

Answer 6

because they have higher than expected boiling points

Question 7

why do alcohols have higher than expected boiling points

Answer 7

because they have hydrogen bonding which forms between alcohol molecules

Question 8

what is the definition for volatility

Answer 8

volatility is the ease with which a liquid turns into a gas . volatility increases as boiling point decreases

Question 9

what happens to boiliing point of the alcohols

Answer 9

boiling point increases with molecular size due to increased london forces . alcohols have higher boiling points than similar molecular mass alkanes due to the added prescence of inter- molecular hydrogen bonding. and more energy is needed to seperatee the molecules

Question 10

what happens to the solubility of alcohols

Answer 10

short chain alcohols are very soluble in water because of the hydrogen bonds that form between alcohol and WATER molecules .
this happens as the OH is polar however solubility decreases as the chain length increases . this is because the carbon chain increases which is non polar and will not form hydrogen bonds with water molecules , therefore reduces the interaction water can make with the alcohol

Question 11

what reactions do alcohols undergo

Answer 11

-combustion
-oxidation
-dehydration
-substitution

Question 12

why is combustion of alcohols good

Answer 12

alcohols make useful fuels
-this is because they have high enphalpies of combustion(lots of energy is released)
-do not contain sulfur so there is less polution
-can be obtained from renewable resources

Question 13

how can alcohols be obtained from renewable resources

Answer 13

-ethanol can be produced from the fermentation of glucose by yeast

Question 14

what flame do alcohols burn in

Answer 14

a light blue flame

Question 15

whats the test for water

Answer 15

-cobalt chloride paper from blue to pink
or
-anhydrous copper sulphate from white to blue

Question 16

what alcohols can be oxidised and how

Answer 16

primary and secondary alcohols can be oxidised by an oxidising agent

Question 17

what is the oxidising agent used

Answer 17

a solution containing acidified dichromate ions

Question 18

how can the oxidising mixture be made

Answer 18

from potassium dichromate K2Cr2O7 and dilute sulfuric acid H2SO4

Question 19

how will we know that oxidation takes place

Answer 19

oxidising agent is orange and turns to green when it reacts to form Cr3+

Question 20

what are the two products that can be formed from oxidation of primary alcohols

Answer 20

aldehyde and carboxylic acid

Question 21

how is an aldehyde made

Answer 21

distill off the aldehyde before it gets oxidised further in distillation , use a excess of the alcohol so that there is insufficient oxidising agent to carry through to a carboxylic acid

Question 22

how is it possible to distill off the aldehyde

Answer 22

the aldehyde has a lower boiling point than the alcohol so it can be distilled off. this is because of the prescence of hydrogen bonds in the alcohol and not in the aldehyde

Question 23

how do we make a carboxylic acid

Answer 23

either use an aldehyde of alcohol in reflux

Question 24

how do we ensure good yeild for making a carboxylic acid

Answer 24

use an excess of the oxidising agent and make sure that the aldehyde formed as the half way product stays in the mixture

Question 25

what will happen in reflux that we just ignore

Answer 25

the oxidising agent will still go green but that does not mean you have otained a carboxylic acid it means you have obtained a aldehyde and need to reflux for longer

Question 26

what happens when the reflux reaction is finished

Answer 26

the carboxylic acid is distilled off

Question 27

what do you need to remeber in reflux and distillation

Answer 27

a molecule of water is produced when an aldehyde or carboxylic acid

Question 28

what are secondary alcohols oxidised into

Answer 28

secondary alcohols are oxidised to ketones and no further

Question 29

what do tertiary alchols get oxidised into

Answer 29

tertiary alcohols do not undergo oxidiation reactions so the acidified dichromate solution remains orange

Question 30

what is dehydration of alcohols

Answer 30

an elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule

Question 31

what do you need for a dehydration reaction

Answer 31

• conc H2SO4 or conc H3PO4
  -reflux at 180

Question 32

what do you produce from dehydration of an alcohol

Answer 32

an alkene and water

Question 33

where do you remove the atoms and add the double bond

Answer 33

you add the double bond between the OH and a H on adjacent molecule forming 2 isomers

Question 34

what is a substitution reaction with an alcohol

Answer 34

substitution reactions occur when a strong acid and a substance that releases halide ions when aqueous is added to an alcohol. This occurs under reflux

Question 35

what are the products in a substituon reaction of an alcohol

Answer 35

haloalkane and water