6.2.5: Organic synthesis Flashcards

1
Q

When purifying by recrystallisation, why is the minimum volume of hot solvent used?

A

So that a saturated solution is created, so that as many crystals will fall out of solution as possible when it is cooled

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why is the solution filtered hot when purifying by

recrystallisation?

A

To remove insoluble impurities and ensure that

the crystals do not form in the filter paper

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why is the solution cooled in an ice bath when

purifying by recrystallisation?

A

To ensure that as many crystals as possible fall

out of solution - yield is higher

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Why are the crystals washed with cold water when

purifying by recrystallisation?

A

To remove soluble impurities

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How would you separate the crystals from the

reaction mixture when purifying by recrystallisation?

A

Filter under reduced pressure using a Buchner

funnel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why might percentage yield be below 100%

(practical reasons)?

A

Product is lost during filtration, drying and weighing - spills,
not all transferred from one piece of apparatus to the other
Product is left dissolved in the solution - some does not
crystallise. Some left on filter paper. Sample still wet

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe how Quickfit apparatus is connected.

A

Grease the joints using some petroleum
jelly on the inside of the joints before
connecting the pieces together.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

In a distillation setup, why is it necessary to have a continuous water flow around the condenser?

A

So that the water remains cool in order for the mixture to be distilled

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe a method that can be used to separate immiscible liquids.

A

●Pour the mixture into a separating funnel and some distilled water
● Add the stopper and invert the flask to mix the mixture
● Equalise the pressure by opening the stopper as required
● Continue shaking until there is no ‘whistle’ sound
● To collect the water in the lower layer, open the stopper and place a beaker under the spout
● Use another beaker to collect the desired organic layer
● Shake the liquid with some drying agent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Name two drying agents.

A

Magnesium sulphate and Calcium chloride

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How is a drying agent used?

A

● Add a selected drying agent to the organic product
● If the drying agent forms clumps add some more until they are moving freely
● Use gravity filtration to collect the dry product.
● Filtrate is the product

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does re-distillation mean?

A

When a liquid is purified by using multiple distillations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the three key steps to purify an organic solid?

A
  1. filtration under reduced pressure
  2. recrystallisation
  3. measurement of melting points
How well did you know this?
1
Not at all
2
3
4
5
Perfectly