Module 4 Chapter 16 Flashcards
What are the types of reaction that require heating under reflux
This is for making carboxylic acids from primary alcohols, ketones from secondary alcohols, dehydration of alcohols and substitution of alcohols.
What does heating under reflux do
It overcomes the activation energy increasing the rate of reaction
What does heating under reflux not do
It doesn’t aggressively boil reactants and products
What do you need when heating under reflux
Round-bottom or pear shaped flask
Condenser
Rubber tubing
Stand and clamp
Heat source - usually a Bunsen burner, tripod and gauze
What are some features of heating under reflux
It is carried out at a fixed temperature
If it is under 100 degrees a water bath can be used
And a heating mantle can be used for flammable liquids
Anti bumping granules can be added to flask so the contents will boil smoothly
How is the condenser arranged when heating under reflux
It is kept upright and clamped loosely as the outer glass is fragile
No stopped on top of the condenser to prevent the build up of pressure
Water enters at the bottom and exits at the top of the Leibig condenser
How does the condenser work
The vapour rises and then passes into the condenser where it is cooled and drips back into the flask
What is distillation
It is a method to separate a pure liquid from its impurities
What is required for distillation
Condenser
Round bottom or pear shaped flask
Rubber tubing
Heat source
Stand and clamp
Thermometer
Still head
Receiving adapter
Screw cap adapter
How is a distillation set up
The flask is clamped by neck and still head connected to the flask
The still head adapter is T shaped and has two joints one for the screw cap adapter and one for the condenser
The second clamp is placed and the round receiver adapter at the point at which it is attached to the condenser
What is used to collect the product and what is the product called
A flask is used to collect the distillate
What is the process of the distillation
The flask is heated and the mixture will start to boil
Different liquids in the mixture will have different BPs
Lowest BP is the most volatile and boils first
Vapour moves out of the flask and into the condenser where it will cool back to a liquid and drip into the collecting flask.
DRAW THE EXPERIMETN FOR DISTILLATION
DRAW THE EXPERIMENT FOR REFLUX
How are different layers of liquid separated
Using a separating funnel
What are the steps when using a separating funnel (1)
1)Ensure the tap of the separating funnel is closed
2)Pour the mixture of liquids into the separating funnel and place a stopper at the top of the funnel, invert to mix
3) allow the layers to settle
4) add some water to see which layer increases in volume and this is the aqueous layer
What are the steps when using a separating funnel (2)
- 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
- Place a second conical flask under the separating funnel to collect the other layer
- Have one conical flask with the organic layer and one with the aqueous labelled properly
What may be leftover in the organic liquid and why
Preparation of organic liquid often involves acids, so there may be acids in your impure product.
What are the steps to remove the acids present
Add aqueous sodium carbonate, shake in a separating funnel
The acid will react with the sodium carbonate forming carbon dioxide gas
Open the tap slowly holding the separating funnel upside down to release any gas produced
Use the separating funnel to remove the aqueous sodium carbonate layer and the organic layer should be washed with water before running both layers off
How do you dry the water present
Add a drying agent to the organic liquid - anhydrous inorganic salt
This readily takes up water becoming hydrated.
What are the steps to dry the organic product
1) Add organic liquid to conical flask
2) using spatula add during agent to liquid and gently swirl to mix
3) Place stopper on flask - stopping evaporation and leave for 10 minutes
4) If solid is in one lump there is still water add move or the drying agent until some of the solid is dispersed in the solution as fine powder
5) Decant liquid from solid into another flask, if liquid is dry it should be clear.
What are some common inorganic slats used and for what
Anhydrous calcium chloride - drying hydrocarbons
Anhydrous calcium sulphate - general drying
Anhydrous magnesium sulphate - general drying
Why is re-distillation sometimes required
Some organic liquids have boiling points that are very similar
So the sample may be impure
How should redistillation be done
Clean and dry the distillation apparatus for carrying out a second distillation
Now only collect the product with the boiling points of the desired compounds
The narrower the boiling range the purer the product.
