16) Organic synthesis

Question 1

Name 5 key quickfit apparatus that are often used in organic synthesis

Answer 1

round-bottom or pear-shaped flask
receiver
screw-tap adaptor
condenser
still head

Question 2

Define reflux

Answer 2

the continual boiling and condensing of a reaction mixture back to the original container to ensure that the reaction takes place without the contents of the flask boiling dry

Question 3

State 3 key things that heating under reflux helps to achieve

Answer 3

overcome activation energy
increase rate of reaction
prevent volatile components from escaping

Question 4

Name 5 key apparatus used in a reflux

Answer 4

rubber tubing
Liebig condenser
clamp + stand
pear-shaped flask
heat source

Question 5

In reflux, what should the direction of water flow ensure?

Answer 5

that the outer jacket of the condenser is full

Question 6

In reflux, what is the rubber tubing connected to?

Answer 6

the inlet of the condenser

the outlet of a sink

Question 7

Why should a Liebig condenser be clamped loosely?

Answer 7

very fragile

Question 8

Why should a stopper not be placed on a Liebig condenser when undergoing reflux?

Answer 8

may explode

Question 9

Why are the joints of some quickfit apparatus greased before use and then rotated back and forth when connecting to another piece of apparatus?

Answer 9

to ensure a good seal which comes apart easily after the experiment

Question 10

What should be added to the reaction mixture in reflux to allow it to boil smoothly?

Answer 10

anti-bumping granules

Question 11

What heat source without a naked flame could be used for reflux when heating flammable liquids?

Answer 11

a heating mantel

Question 12

For reflux, should water go into a Liebig condenser at the top or the bottom?

Answer 12

at the bottom

Question 13

Define distillation

Answer 13

common method to separate a pure liquid from its impurities (once reflux is complete)

Question 14

Name 5 pieces of apparatus not used for reflux, that will be needed to carry out a distillation

Answer 14

thermometer
screw-cap adaptor / thermometer pocket
still head
receiver
conical flask

Question 15

What is important about the use of a conical flask in a distillation?

Answer 15

means that the apparatus is not completely airtight

Question 16

What property of a mixture of liquids is important for distillation to work? Why?

Answer 16

different boiling points
the liquid with the lowest boiling point is the most volatile and will boil first, when the vapours reach the condenser they will condense

Question 17

Describe the steps for purifying an organic product after distillation

Answer 17

1) ensuring separating funnel tap is closed, pour in mixture, place in stopper and invert to mix contents. allow to settle
2) identify aqueous layer (increases in volume when water is added)
3) place a conical flask under the separating funnel, remove the stopper and open the tap to allow the lower layer to be collected. repeat with a second conical flask for the other layer. label flasks

Question 18

What extra steps would be needed for the purification of an organic product if the preparation has used acids?

Answer 18

1) add aqueous sodium carbonate and shake the mixture in the separating funnel to remove an acid impurities
2) slowly open the tap whilst holding the funnel upside down to release any pressure as CO2 is produced
3) remove the aqueous carbonate layer and wash the organic layer with water

Question 19

Define drying agent

Answer 19

an anhydrous inorganic salt that readily takes up water to become hydrated

Question 20

Name a drying agent for drying hydrocarbons

Answer 20

anhydrous CaCl2

Question 21

Name 2 drying agents for general drying

Answer 21

anhydrous CaSO4

anhydrous MgSO4

Question 22

Give the 4 steps for drying an organic product

Answer 22

1) using a spatula, add drying agent to the organic layer in the conical flask and gently swirl to mix together
2) place on a stopper (prevent evaporation) and leave for 10 mins
3) If the solid has 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
4) decant the liquid from the solid into another flask. if the liquid is dry it should be clear

Question 23

Why would you dry an organic product?

Answer 23

to remove traces of water

Question 24

When carrying out a second distillation what change would you make?

Answer 24

collect only the product with the boiling point of the compound you are trying to make

Question 25

The _ the boiling range, the purer the product.

Answer 25

narrower

Question 26

Define organic synthesis

Answer 26

the preparation of complex molecules from simple starting materials

Question 27

haloalkane -> alcohol

Answer 27

NaOH(aq)

reflux

Question 28

alkane -> haloalkane

Answer 28

halogen/UV

Question 29

alkene -> haloalkane

Answer 29

hydrogen halide

Question 30

alkene -> alcohol

Answer 30

H2O(g)

H3PO4 catalyst

Question 31

alkene -> alkane

Answer 31

H2

Ni catalyst

Question 32

alcohol -> haloalkane

Answer 32

sodium halide + H2SO4

Question 33

alcohol -> alkene

Answer 33

conc. H2SO4

Question 34

primary alcohol -> carboxylic acid

Answer 34

K2Cr2O7/H2SO4 reflux

Question 35

primary alcohol -> aldehyde

Answer 35

K2Cr2O7/H2SO4 distil

Question 36

secondary alcohol -> ketone

Answer 36

K2Cr2O7/H2SO4 reflux

Question 37

Define target molecule

Answer 37

the compound the chemist is attempting to prepare by organic synthesis

Question 38

Describe how you would prepare to carry out a two-step synthesis

Answer 38

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