organic synthesis chp 16

Question 1

what pieces of apparatus are needed to heat something under reflux

Answer 1

-round-bottom or pear-shaped flask
-condenser
-rubber tubing
-stand and clamp
-heat source (usually a Bunsen burner, tripod, gauze or heating mantle)

Question 2

what is an alternative method of heating a reaction if the reaction can occur at below 100°C

Answer 2

a water bath can be used

Question 3

what can be used in a reaction involving flammable liquids that is safer than the normal reflux set up

Answer 3

a heating mantle can be used so that there Is no naked flame present, this provides an added level of safety should any of the apparatus leak or crack

Question 4

what is the purpose of anti-bumping granules

Answer 4

• added to liquid before flask is heated so that the contents will boil smoothly
• if not used, bubbles form at bottom of liquid and make the flask vibrate and jump

Question 5

why should you never put a stopper on top of the condenser when completeing reflux

Answer 5

if you put a stopper on the condenser, you would have a closed system and pressure would build up inside as the heated air expand. this could result in the apparatus exploding

Question 6

which way should the flow of water be in the condenser

Answer 6

water always enters the condenser at the bottom and leaves at the top to ensure that the outer jacket is full

Question 7

what does heating under reflux enable a reaction (liquid) to do

Answer 7

heating under reflux enables a liquid to be continually boiled whilst the reaction takes place. This prevents volatile components from escaping and the flask from boiling dry. The vapour from the mixture rises and condenses and drips back down into the flask

Question 8

what apparatus is needed to complete a distillation reaction

Answer 8

-round-bottom or pear-shaped flask
-condenser
-rubber tubing
-heat source
-stand and clamp
-screw-cap adaptor
-receiver adaptor
-still head
-thermometer

Question 9

what is the purpose of distillation

Answer 9

distillation is a method used to separate a liquid from its impurities

Question 10

what is an easy way to identify an organic layer an organic liquid and water/aqueous layer

Answer 10

an easy way to identify the organic layer is to add some water to your mixture, the layer that gets bigger is the aqueous layer

Question 11

what are the steps to using a separating funnel to separate the organic layer from the aqueous layer

Answer 11

1) ensure that 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 mix the contents
3)allow the layers to settle
4)add some water to see which layer increase 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 separating funnel to collect the other layer
7)you will now have 1 conical flask containing the organic layer and another containing the aqueous layer, label the flasks so that you don’t muddle them

Question 12

in preparations using acids, what can be used to remove the acid impurities

Answer 12

these can be removed by adding aqueous sodium carbonate and shaking the mixture in the separating funnel.
the aqueous sodium carbonate layer is removed

Question 13

what is a drying agent

Answer 13

a drying agent is an anhydrous inorganic salt that readily takes up water to become hydrated

Question 14

what are some common drying agents

Answer 14

• calcium chloride, CaCl2, for hydrocarbons
• calcium sulphate, CaSO4, for generally drying

Question 15

why would drying agents be needed

Answer 15

there may be some water left in the organic product

Question 16

what is the procedure for drying an organic liquid

Answer 16

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 10 minutes
4)if the solid has all stuck together in a lump, there is still some water present. Add more drying agent until some solid is dispersed in the solution as a fine powder
5)decant the liquid from the solid into another flask. if the liquid is dry it should be clear

Question 17

what is redistillation

Answer 17

the process of distilling a liquid again

Question 18

why would you redistile a substance

Answer 18

sometimes organic liquids have boiling points that are relatively close together, so your prepared sample may still contain some organic impurities

Question 19

whats the difference between distillation and redistillation

Answer 19

you only collect the product with the boiling point of the compound you are trying to make, the narrower the boiling range, the purer the product

Question 20

what is organic synthesis

Answer 20

organic synthesis is the preparation of complex molecules from simple starting materials.

Question 21

what are the functional groups of compounds in AS a level chemistry

Answer 21

Question 22

what is meant by the term target molecule

Answer 22

the term target molecule is used to describe the compound that the chemist is attempting to prepare by organic synthesis

Question 23

how would you convert a starting molecule into the target molecule

Answer 23

-identify the functional groups in your starting and target molecules
-identify the intermediate that links the starting and the target molecules
-state the reagents and conditions for each step

Question 24

what is ozonolysis

Answer 24

a technique used in organic chemistry to break open a C=C double bond.