Organic practical work

Question 1

Describe how the student would prepare the standard solution, naming apparatus and method (3 marks)

Answer 1

• Dissolve solid in (distilled) water (less than 250 cm3) in beaker
• Transfer (solution) to volumetric flask AND Transfer washings (from beaker) to flask
• Make up to mark/up to 250 cm3 with (distilled) water AND Invert flask (several times to ensure mixing)

Question 2

What does recrystallisation do

Answer 2

Purifies solids

Question 3

What is the first step in recrystallisation

Answer 3

Dissolve solid in the minimum volume of hot solvent

Question 4

After you’ve dissolved the solid in hot solvent when recrystallising, what is the next step

Answer 4

Allow the solution to cool down slowly, crystals will start to form

Question 5

What is the name of the flask involved in reduced pressure filtration

Answer 5

Buchner

Question 6

After allowing the solution to cool when recrystallising, what is the next step

Answer 6

Filter to remove the impurities in the solution and obtain the purified solid crystals

Question 7

What is used to wash the purified crystals

Answer 7

Very cold solvent

Question 8

Why must the solvent be cold when washing the crystals after recrystallisation

Answer 8

So solid product doesn’t dissolve again

Question 9

What is the final step in recrystallisation

Answer 9

Leave crystals to dry

Question 10

If a substance contains impurities, will the melting point be lower or higher than data book values

Answer 10

Lower

Question 11

If the substance contains impurities, will the temperature range be smaller or larger than data book values

Answer 11

Larger range

Question 12

What is the typical reaction of alkanes

Answer 12

Radical substitution

Question 13

What is the typical reaction of alkenes

Answer 13

Electrophilic addition

Question 14

What are the properties of alkenes

Answer 14

• Electron rich double bond
• Non-polar bond

Question 15

What are the properties of aromatic compounds

Answer 15

• Delocalised electron ring
• Stable

Question 16

What is the typical reaction of aromatic compounds

Answer 16

Electrophilic substitution

Question 17

What are the 2 properties of alcohols

Answer 17

• Lone pair on oxygen can act as a nucleophile
• Polar C-OH bond

Question 18

What are the 2 typical reactions with alcohols

Answer 18

• Esterification and nucleophilic substitution
• Dehydration/ elimination and nucleophilic substituion

Question 19

What is the property of haloalkanes

Answer 19

Polar C-X bond

Question 20

What is the typical reaction involving haloalkanes

Answer 20

Nucleophilic substitution and elimination

Question 21

Properties of nitriles

Answer 21

Electron deficient carbon centre

Question 22

Typical reaction of nitrile

Answer 22

Reduction and hydrolysis

Question 23

Properties of amines

Answer 23

Lone pair on the nitrogen is basic, can act as a nucleophile

Question 24

Typical reaction of amines

Answer 24

Nucleophilic substitution and neutralisation

Question 25

Properties of aldehydes and ketones

Answer 25

Polar C=O bond

Question 26

Typical reactions of carbonyls (3 things)

Answer 26

- Nucleophilic addition - Oxidation of aldehydes - Reduction

Question 27

Property of carboxylic acids

Answer 27

Electron deficient carbon centre

Question 28

Typical reactions of carboxylic acids

Answer 28

- Esterification and neutralisation

Question 29

Properties of esters

Answer 29

Electron deficient carbon centre

Question 30

Typical reactions of esters

Answer 30

Hydrolysis

Question 31

Typical reaction of acid anhydride

Answer 31

Esterification

Question 32

Property of acid anhydride

Answer 32

Electron deficient carbon centre

Question 33

Typical reactions of acyl chloride

Answer 33

- Nucleophilic addition-elimination - Condensation - Friedel-Crafts acylation

Question 34

Property of acyl chloride

Answer 34

Electron deficient carbon centre.

Question 35

What 3 functional groups are involved in addition reactions

Answer 35

- Alkene - Aldehyde - Ketone

Question 36

What are the 3 functional groups involved in substitution reactions

Answer 36

- Halogens - Benzene (H is substituted) - Alcohol

Question 37

What 2 functional groups are involved in elimination reactions

Answer 37

- Halogens - Alcohols

Question 38

What 4 functional groups are involved in condensation reactions

Answer 38

- Acyl chloride - Carboxylic acids - Amides - Alcohols

Question 39

What 2 functional groups are involved in hydrolysis reactions

Answer 39

- Esters - Acid anhydride

Question 40

What are the 2/3 functional groups that can be oxidised

Answer 40

- Primary alcohol - Aldehyde - Secondary alcohol

Question 41

What is reduction in terms of electrons

Answer 41

The gain of electrons

Question 42

Explain how TLC could be used to monitor the course of a reaction (2 marks)

Answer 42

Take samples from reaction mixture at regular intervals Spot/run on a TLC plate, alongside cyclohexanol (and cyclohexanone) controls 9

Question 43

Plan an experiment to identify the pure organic ketone (3 marks)

Answer 43

React (sample of distillate) with 2,4-dinitrophenylhydrazine recrystallise AND determine the melting point Compare melting point to known/library value for cyclohexanone (derivative)

Question 44

What are the steps to purify a liquid

Answer 44

* Add a neutralising agent by formula or name e.g. Na2CO3 * In separating funnel, organic layer is on top (as less dense as stated in original question * Drying with an anhydrous salt by formula or name, e.g. MgSO4, Na2SO4, CaCl2 * Redistil

Question 45

Draw a distillation

Answer 45

distillation flask heat source thermometer at outlet (bulb level with outlet) still-head water condenser (correct direction of water flow) receiving vessel open system.

Question 46

A reactant in solution reacts to form a solid. How can the solid be isolated (1 mark)

Answer 46

Filtration

Question 47

How can the solid be purified (1 mark)

Answer 47

Recrystallisation

Question 48

How could the purity of the solid be checked (1 mark)

Answer 48

TLC or melting point measurement

Question 49

How to separate a liquid product (1 mark)

Answer 49

Separating funnel

Question 50

Organic liquid may still have some water present. How can this be removed before purification (1 mark)

Answer 50

By adding a (solid) drying agent (such as Na2SO4/MgSO4/CaO) Filtering off the unwanted solid

Question 51

How can the liquid be purified (1 mark)

Answer 51

Distillation

Question 52

How could the purity of the dry liquid be checked, after purification (1 mark)

Answer 52

Chromatography

Question 53

A reaction in aqueous solution forms a slat that is soluble in water. The aim is to isolate the acid of the salt and then purify it. The acid is a liquid that is not soluble in water. How can the acid be formed and then isolated (1 mark)

Answer 53

Add acid then separating funnel

Question 54

How can the acid be purified (1 mark)

Answer 54

Distillation

Question 55

How can the purity of the liquid be checked (1 mark)

Answer 55

Chromatography

Question 56

List the equipment used in a reflux (3 marks)

Answer 56

Round-bottomed or pear-shaped flask (1) Condenser (1) Anti-bumping granules (1

Question 57

How could we carry out a quick test to distinguish an aldehyde from a ketone (2 marks)

Answer 57

Tollens: warm with Tollens reagent (or AgNO3/NH3) (1) Silver mirror (1)

Question 58

How could we carry out a quick test to distinguish an alcohol from a ketone (2 marks)

Answer 58

Cr2O72-/H+ (1) Orange to green (1) Allow DNPH/organe ppte for (2)

Question 59

How could we carry out a quick test for a haloalkane that also identifies the halide (3 marks)

Answer 59

AgNO3 (HNO3) (1) NaOH (1) White, cream or yellow precipitate (1) (redissolves in conc. NH3 if AgBr and in dil. NH3 if AgCl)

Question 60

How could we carry out a quick test for a carboxylic acid (2 marks)

Answer 60

Na2CO3 (1) Effervescence (1)

Question 61

How could we carry out a quick test for phenol but not benzene (3 marks)

Answer 61

Br2 (aq) (1) Decolourised bromine (1) White precipitate (1)

Question 62

Esterifcation happens when an alcohol and a carboxylic acid are reacted together. The product ester will often have a boiling point above room temperature and is also often immiscible with water. Esters are typically less dense than water. Carboxylic acids and alcohols will dissolve in water, as will the catalytic acid. Write down the steps required to purify an ester, and to ensure that no alcohol, carboxylic acid or catalytic acid remain in the product (6 marks)

Answer 62

Separating funnel (1) Collect non-aqueous TOP layer (1) (mark for stating product is the top layer) Wash in funnel with aq. Na2CO3/NaHCO3 (open tap to allow gas to escape) (1) Dry organic layer with drying agent (1) Filter (1) Distil (1)