Chapter 16 (approved)

Question 1

Apparatus to heat under reflux:

Answer 1

1 Condenser
2 Rubber tubing
3 Stand and clamp
4 Heat source
5 Round-bottom flask

Question 2

When can a water bath be used for a reflux reaction?

Answer 2

When the reaction can happen under 100 degrees Celsius

Question 3

What must you do when heating a flammable liquid under reflux and why?

Answer 3

Use a heating mantle instead of a Bunsen burner in case of a leak of crack in the apparatus

Question 4

When do you add the reaction mix and anti-bumping granules in reflux?

Answer 4

Before fitting the condenser

Question 5

Why are anti-bumping granules added in reflux?

Answer 5

So the contents will boil smoothly, preventing large bubbles from forming at the bottom of the liquid which makes the glassware vibrate and jump violently

Question 6

What is applied to the ground glass joints in reflux and why?

Answer 6

A thin layer of grease is applied to the apparatus so it comes apart easily after the experiment

Question 7

Why do you gently rotate the condenser back and forth in the reflux method?

Answer 7

To provide a good seal and ensure the apparatus comes apart easily at the end

Question 8

Why should condenser be clamped loosely in reflux?

Answer 8

Because the glass outer jacket is fragile and easily broken

Question 9

Why don’t you put a stopper in the top of the condenser in reflux?

Answer 9

So the system isn’t closed which would build up pressure inside and cause the apparatus to explode

Question 10

What is rubber tubing used for in reflux?

Answer 10

To connect the inlet of the condenser to the tap and the outlet to the sink

Question 11

What does heating under reflux enable and prevent and how?

Answer 11

It enables a liquid to be continually boiled whilst the reaction takes place. This prevents volatile components from escaping and the flask boiling dry. The vapour rises up the inner tube of the condenser until it meets the outer jacket containing cold water. The vapour then condenses and drops back into the flask.

Question 12

Why is distillation done and what does it separate?

Answer 12

Once reflux is complete, the product in the flask needs to be purified to remove remaining reactants or by-products. It is used to separate a pure liquid from its impurities.

Question 13

Distillation apparatus:

Answer 13

Round bottom flask
Condenser
Rubber tubing
Heat source
Stand and clamp
Screw-cap adaptor
Receiver adapter
Still head
Thermometer

Question 14

How is the apparatus set up for distillation?

Answer 14

The flask is clamped by its neck and the still head is connected to the flask.
The joints are greased.
A second clamp placed round the receiver adaptor where it is attached to the condenser
The rubber tubing is used to connect the inlet of the condenser to the tap and the outlet to the sink, the one on top is the outlet
A flask is placed under the exit of the receiver

Question 15

Describe the still-head adaptor:

Answer 15

The still-head adaptor is T shaped and has 2 ground-glass joints, one for the screw-cap adaptor and one for the condenser.

Question 16

What happens in distillation? (4)

Answer 16

The flask is heated and the mixture in the flask will start to boil
The different liquids in the mixture will have different boiling points, so the lowest boiling point liquid (most volatile) will boil first
The vapour moves out of the flask up into the inner tube of the cold condenser, where it condenses and becomes liquid, and the drips into the collecting flask

Question 17

Why is a flask used to collect the distillate?

Answer 17

So the distillation apparatus is not completely airtight

Question 18

What issues may occur when preparing samples of organic liquids and how can you tell this has happened?

Answer 18

Water may be obtained along with the product, in which case you will see two liquid layers inside the collection flask

Question 19

Separating the organic and aqueous layers with a separating funnel method:

Answer 19

1 Ensure the tap of the separating funnel is closed
2 Pour the mixture of liquids into the separating funnel, place a stopper in the top of the funnel, and invert to mic the contents
3 Allow the layers to settle
4 Add water to see which layer increases in volume - this is the aqueous layer
5 Place the 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 separating funnel to collect the other layer
7 You will now have one conical flask containing the organic layer and another containing the aqueous layer. Label the flasks so you don’t muddle them

Question 20

How to remove acid impurities?

Answer 20

Add aqueous sodium carbonate and shake the mixture in a separating funnel
Any acid present will react with sodium carbonate and release carbon dioxide gas.
The tap needs to be slowly opened, holding the stoppered separating funnel upside down to release any built up gas pressure
Then remove the aqueous sodium carbonate layer and wash the organic layer with water, then run both layers into separate flasks

Question 21

Most common drying agents and their use

Answer 21

Anhydrous calcium chloride: drying hydrocarbons

Anhydrous calcium sulfate: general drying

Anhydrous magnesium sulfate: general drying

Question 22

Why and how do you dry organic products?

Answer 22

There may be some traces of water left, so you add a drying agent which takes up water to become hydrated

Question 23

Procedure for drying an organic liquid:

Answer 23

1 Add the organic liquid to a conical flask
2 Using a spatula, add some of the drying agent to the liquid and gently swirl the contents to mix together.
3 Place a stopper on the flask to prevent your product from evaporating away, leave for about ten minutes
4 If the solid has all stuck together in a lump, there is still water present, so add more drying agent until some solid is dispersed in the solution as a fine powder
5 Pour the liquid in another flask to separate from the solid. If the liquid is dry it should be clear

Question 24

Why is redistillation performed?

Answer 24

If organic impurities are formed due to the organic liquids having boiling points which are close together

Question 25

Describe the process of redistillation:

Answer 25

The distillation apparatus is cleaned and dried and set up again. This time, only collect the product with the boiling point of the compound you are trying to make.