16.1 Practical techniques in organic chemistry

Question 1

What apparatus are needed for reflux?

Answer 1

-Round-bottom or pear shaped flask
-Condenser
-Rubber tubing
-Stand and clamp
-Heat source (usually a bunsen burner, tripped and gauze or a heating mantle)

Question 2

When is a water bath used for reflux?

Answer 2

If the reaction can be carried out in below 100°, to control temperature

Question 3

Draw a diagram of reflux apparatus

Answer 3

Question 4

When would you use a heating mantle for reflux?

Answer 4

For heating flammable liquids, so there is no naked flame

Question 5

Why are anti-bumping granules added to the mixture in a reflux?

Answer 5

So that the contents boil smoothly ,preventing violent bubbling

Question 6

What may happen if anti-bumping granules are not used?

Answer 6

Large bubbles form a the bottom of the liquid, make glassware vibrate or jump violently

Question 7

Why is a stopper not put in reflux apparatus?

Answer 7

There will be a closed system, pressure would build up inside as heated air expands, can result in apparatus exploding

Question 8

Where does water enter the condenser in a reflux?

Answer 8

At the bottom, leaves at the top to ensure the outer jacket is full

Question 9

What does heating under reflux allow?

Answer 9

A liquid to be boiled continually whilst a reaction takes place, preventing volatile liquids from escaping the flask and the flask from boiling dry

Question 10

How does vapour not escape in reflux apparatus?

Answer 10

It rises up the inner tube of the condenser until it meets the outer jacket containing water, the vapour then condenses and drips back into the flask

Question 11

What are the apparatus needed for distillation?

Answer 11

-Round bottom or pear shaped flask
-Condenser
-Rubber tubing
-Heat source
-Stand and clamp
-Screw-cap adaptor
-Still head
-Thermometer

Question 12

Draw a diagram of distillation apparatus

Answer 12

Question 13

Where does water enter in distillation apparatus?

Answer 13

Water enters condenser at lowest point (closest point to receiver adaptor)

Question 14

How does distillation work?

Answer 14

-Used to separate different liquids in a mixture to prevent further substitution and identify the boiling point
-The liquid with the lowest boil is the most volatile and will boil first

Question 15

How do you identify the organic layer (when purifying organic products)?

Answer 15

Add some water to the separating funnel, the layer that gets bigger is the aqueous layer

Question 16

What apparatus is used to separate the aqueous and organic layers?

Answer 16

Separating funnel

Question 17

How do you separate the aqueous and organic layer?

Answer 17

1. Ensure the tap of separating funnel is fully closed
2. Pour the mixture of liquids into the separating funnel, place a stopped in the top and invert the contents
3. Allow the layers to settle
4. Add some water to see which layer increases in volume - this is the aqueous layer
5. Place a conical flask under the separating funnel, remove the stopper and open the tap until the whole of the lower layer has left the funnel
6. Place a second conical flask under the funnel to collect the second layer
7. Label the flask so you do not muddle them up

Question 18

Draw

Answer 18

-When two organic liquids have boiling points close to each other, sample may contain some organic impurities
-Distillation apparatus is cleaned and tried and reset up and a second distillation is carried out
-This time only collect the product with the boiling point of the compound you are trying to make

Question 19

How are acid impurities removed when preparing organic products?

Answer 19

1. Add aqueous sodium carbonate (Na2CO3) and shaking the mixture in a separating funnel
2. Any acid will react with the sodium carbonate releasing CO2
3. The tap needs to be slowly opened, holding the stopped funnel upside down to realise any gas pressure
4. Aqueous sodium carbonate layer is removed
5. Organic layer is washed with water before separating off both layers into separate conical flaks

Question 20

What are the steps for purifying an organic liquid ?

Answer 20

1. Neutralise acid, add NaHCO3 (base)
   observation: effervescence
2. Remove water using separating funnel to remove aqueous layer
3. Add CaCl2 until evenly dispersed then filter
4. Distill at specific temperature to separate organic products

Question 21

How are traces of water remvoed from organic products?

Answer 21

Using drying agents

Question 22

What are examples of drying agents?

Answer 22

anhydrous calcium chloride - CaCl2
anhydrous calcium sulfate - CaSO4
anhydrous magnesium sulfate - MgSO4

Question 23

Why is CaCl2 used as a drying agent?

Answer 23

When drying hydrocarbons

Question 25

What are the steps for drying an organic liquid?

Answer 25

Question 26

When is redistillation used?

Answer 26

-When two organic liquids have boiling points close to each other, sample may contain some organic impurities -Distillation apparatus is cleaned and tried and reset up and a second distillation is carried out -This time only collect the product with the boiling point of the compound you are trying to make