Practical techniques in organic chemistry - Part 1

Question 1

heating under reflux should be used when :

Answer 1

• when a reaction involving an organic compound is slow at room temperature
• at least one of the compounds involved is volatile
• used as a means of reacting substances together, usually organic compounds

Question 2

heating under reflux prevents volatile compounds from escaping by

Answer 2

fitting a reflux condenser which condenser vapour back into liquids so that they return to the flask so that unreacted compounds can react

Question 3

…………………….are added when heating under reflux because:

Answer 3

anti-bumping granules

create nucleic sites for bubbles to form, so provides a smoother boiling

Question 4

three methods of separation involving heat are:

Answer 4

• simple distillation
• steam distillation
• fractional distillation

Question 5

simple distillation is used to

Answer 5

obtain a liquid product from a reaction mixture that has a boiling temperature much lower than the other substances in the reaction mixture

Question 6

the method for simple distillation is :

Answer 6

• attach flask with reaction mixture to a condenser, with a thermometer between the links
• heat and use thermometer to monitor temperature so that you know only one product is being distilled
• heat until temperature changes

Question 7

steam distillation is a technique used to :

Answer 7

to separate an insoluble liquid from an aqueous solution

Question 8

steam distillation method:

Answer 8

• pass steam into a reaction mixture that contains an aqueous solution and liquid solution that forms a separate layer
• the agitation of the liquid ensures the insoluble liquid and the aqueous solution are on the surface
• this means both form part of the liquid that evaporates
• this is then condensed into a distillate
• this allows for the insoluble liquid to to evaporate at a lower temperature than its usual boiling temperature
• this means there is less chance of decomposition of the desired product

Question 9

fractional distillation is used

Answer 9

where the difference in boiling temperatures is small (less than 25 degrees C)

Question 10

method for fractional distillation is:

Answer 10

• same as for simple distillation, but with a fractionating column containing glass beads to act as a surface on which vapour leaving the column can condense
• vapour undergoes repeated distillation, so provides a better separation