4.8 Organic Synthesis And Analysis

Question 1

What are miscible liquids

Answer 1

Liquids that can fully mix with each other to form a single solution

Question 2

How to separate miscible layers in general

Answer 2

Distillation

Question 3

Simple distillation

Answer 3

• when large difference between boiling temperatures
• heat mixture to boiling temperature of liquid with lower boiling point
• liquid with lower bp turns into gas and moves up into the condenser and cooled by cold water
• gaseous compound condenses into liquid and collected

Question 4

Fractional distillation

Answer 4

• small difference between boiling temperatures (<20 degrees)
• fractionating column is added upright between the mixture in the flask and condenser
• when heated, liquid with higher boiling temperature condenses back into flask before reaching condenser which allows liquid with lower boiling point to be separated

Question 5

Vacuum distillation

Answer 5

• use if substances have high boiling temperatures (>180 degrees)
• low pressure reduces boiling point of liquids and so of heating products to its decomposition temperature

Question 6

Steam distillation

Answer 6

• jet of steam is passed through the reaction mixture
• oils evaporated by jet of steam
• oils and water from steam both condense and are collected
• as the oil and water is immiscible they can be separated using a separating funnel

Question 7

Solvent extraction

Answer 7

• remove solute dissolved in one solvent into another solvent where its solubility is much greater
• add immiscible solvent to an aqueous solution containing the solute
• added solvent extracts most of solute from the water
• the two solvent layers can be separated using a separating funnel
• solvent layer is dried to remove traces of water

Question 8

Using a separating funnel

Answer 8

• ensure tap is closed
• pour mixture into separating funnel
• put a stopper in the top of the funnel
• shake thouroughly
• remove stopper and allow mixture to separate to 2 layers
• open tap to allow lower layer to flow into the beaker

Question 9

How to separate insoluble solids

Answer 9

Filtration

Question 10

Simple filtration

Answer 10

Filter paper and a funnel
Fluted filter paper works more effectively as it allows for faster filtration as there is only one layer of paper and the contact between the paper and funnel is minimised

Question 11

Vacuum filtration

Answer 11

• Buchner funel
• funnel can be connected to an aspirator or vacuum pump, which reduces the pressure in the flask and makes the solvent pass through the filter quicker
• it’s necessary to dampen filter paper before use to make sure it sticks to the flat bed of the funnel

Question 12

How to separate soluble solids

Answer 12

Solid products must be crystallised before it can be separates using filtration and then purified by recrystallisation

Question 13

Process of recrystallisation

Answer 13

1. Dissolve solute in minimum volume of hot solvent
2. Filter the solution hot to remove any insoluble impurities
3. Allow solution to cool to form crystals
4. Filter the mixture to isolate the crystals
5. Wash crystals with a small volume of cold solvent to remove soluble impurities
6. Dry product between 2 pieces of filter paper in an oven set at a temperature below the product’s melting temperature

Question 14

What is a polymerisation reaction

Answer 14

Reaction where several monomer molecules combine to form a long chain polymer

Question 15

Addition polymerisation

Answer 15

• no other products are formed
• main polymer chain only contains carbon

Question 16

Condensation polymerisation

Answer 16

• small molecule such as water is eliminated
• main polymer chain contains atoms other than C such as O or N

Question 17

How are polyesters formed

Answer 17

• esterification reaction between a dicarboxylic acid and a diol
• water is the small molecule eliminated
• monomers are linked together by ester groups and so have oxygen atoms in the main polymer chain

Question 18

How to make polyethylene terephthalate (PET)

Answer 18

Combine ethane-1,2-diol and benzene-1,4-dicarboxylic acid

Question 19

How are polyamides formed

Answer 19

Condensation reaction between a dicarboxylic acid and a diamine
Water is small molecule eliminated
Monomers joined together by amide group and so have N in main polymer chain