Practicals

Question 1

Define a primary/secondary/tertiary alcohol

Answer 1

C-OH where C atom is bonded to 1/2/3 akyl groups

Question 2

Outline the oxidation of primary alcohols through distillation

Answer 2

R-OH +[O] -(distill)-> R-CHO + [O] -(reflux)-> R-COOH

Question 3

Outline the oxidation of primary alcohols through reflux

Answer 3

R-OH + 2[O] -(reflux)-> R-COOH

Question 4

Outline the oxidising agent used for the distillation of primary alcohols

Answer 4

Tollens = silver mirror
or
Fehling’s = brick red

Question 5

Outline a reducing agent for alcohols and/or aldehydes

Answer 5

Kr2Cr2O7
H2SO4

Question 6

Outline the colour change when a primary/secondary alcohol is oxidised with K2Cr2O7

Answer 6

Orange -> green

Question 7

List what’s used for the distillation apparatus

Answer 7

1. Pear shaped flask
2. Anti-bumping granules
3. Bung
4. Thermometer
5. Condenser
6. e- heater
7. Ice bath
8. Flask

Question 8

Why are anti-bumping granules used for distillation/reflux?

Answer 8

Only make small bubbles form = smooth boiling

Question 9

Why is an e- heater used for distillation?

Answer 9

Alcohol used is flammable (risk)

Question 10

Why does H2O in the condenser enter from the bottom and leave the top?

Answer 10

Ensure condenser completely fills

Question 11

Why is an ice bath used at the end of distillation?

Answer 11

Ensure that volatile reactants/products don’t escape as a gas

Question 12

Define reflux

Answer 12

Continual evaporation + condensation

Question 13

List what’s used in the reflux apparatus

Answer 13

1. Pear shaped flask
2. Anti-bumping granules
3. Bung
4. Condenser
5. e- heater

Question 14

What organic liquid is normally purified?

Answer 14

Cyclohexanol -> cyclohexene

Question 15

Which has a higher bp and why? Cyclohexanol or cyclohexene?

Answer 15

Cyclohexanol
Cyclohexanol = H bonds from R-OH
Cyclohexene = VDWs
H bonds > VDWs

Question 16

Outline the steps that occur for the elimination of cyclohexanol (not like usual mechanism)

Answer 16

1. H+ from catalyst (H3PO4) attacked by e- pair on R-OH
2. H of adjacent C to C-OH2 donates e- pair to form C=C
3. e- pair donates to O+ to form cyclohexene, H2O & reformed H+

Question 17

What apparatus is used for the 1st stage of purification of an organic liquid?

Answer 17

Distillation

Question 18

Outline the 2nd step of the purification of an organic liquid

Answer 18

Add a base (Na2CO3) to neutralise H3PO4 -> open tap to release CO2

Question 19

Outline the 3rd step of the purification of an organic liquid and it’s purpose

Answer 19

Put mixture in separating funnel
Cyclohexanol = top layer
H3PO4(aq) = bottom layer (more dense)
Cyclohexanol separates
Use tap to drain (aq) layer

Question 20

Outline the 4th step of the purification of an organic liquid

Answer 20

+ drying agent (CaSO4) to absorb H2O & other aqueous substances

Question 21

Outline the 5th step of the purification of an organic liquid

Answer 21

Distill again

Question 22

Outline the organic solid that’s normally purified

Answer 22

Aspirin

Question 23

Outline the 4 steps of the preparation of Aspirin

Answer 23

1. 6.0g of salicylic acid added to conical flask + 10cm3 ethanoic anhydride + 5 drops conc H2SO4
2. Mixture swirled & held in warm water bath @ 60°C 20min
3. Flask cools & contents added to 75cm3 cold H2O - aspirin crystallises
4. Aspirin put in Buchner filtration & dries

Question 24

Outline the reagents and mechanism that occurs for the formation of Aspirin

Answer 24

2-hydroxybenzoic acid + ethanoic anhydride
Nucleophilic addition elimination

Question 25

Outline the steps for the nucleophilic addition elimination to form aspirin

Answer 25

1. :OH on 2-hydroxybenzoic acid attacks C+ on ethanoic anhydride - C=O breaks 2. O-H on acid breaks to remove O+. :O- on anhydride forms C=O again, breaking C-O bond Aspirin forms 3. H+ from O-H forms with broken of CH3COO- from anhydride to form CH3COOH

Question 26

What practical is used for the purification of an organic solid?

Answer 26

Recrystallisation

Question 27

Outline the 1st step of the purification of an organic solid

Answer 27

Dissolve aspirin in min amount of hot solvent (ethanol)

Question 28

Outline the 2nd stage of the purification of an organic solid

Answer 28

Gravity filtration - remove insoluble impurities Use funnel and filter paper

Question 29

Outline the 3rd stage of the purification of an organic solid

Answer 29

Put solvent, aspirin & soluble impurities in ice bath Aspirin crystallises out

Question 30

Outline the 4th stage of the purification of an organic solid

Answer 30

Wash aspirin in ice cold solvent under reduced Pa Use Buchner flask and vacuum

Question 31

How do you compare a pure organic solid to an impure organic solid?

Answer 31

MP determination - compare to databook Pure - high MP and low range Impure - low MP & high range

Question 32

How do you make unknown substances in chromatography visible at the end?

Answer 32

Use Ninhydrin