PAG 5.1- Preparing and purifying a haloalkane from an alcohol

Question 1

Method (preparation)

Answer 1

• Measure out volume of alcohol in measuring cylinder and weigh measuring cylinder and it’s contents.
• Pour alcohol into separating funnel, then reweigh measuring cylinder to find exact mass of alcohol used.
• Measure 20cm^3 of concentrated hydrochloric acid and add gradually to separating funnel.
• Place the stopper on separating funnel and shake vigorously for 20 minutes, releasing pressure when required.

Question 2

Method (separation)

Answer 2

• Allow layers to separate in funnel.
• Once separated, remove the stopper and open the tap to collect the bottom aqueous layer.
• Once layer is removed, close tap and add sodium hydrogencarbonate solution to the funnel in small portions, neutralises any remaining acid.
• Shake funnel after each addition and release pressure, continue until no more bubbles.
• Allow layers to separate and remove bottom aqueous layer.
• Collect organic layer in 100cm^3 conical flask and add anhydrous sodium sulfate slowly, while swirling until liquid becomes clear.
• Filter the solution through filter paper into a round-bottom flask.

Question 3

Method (distillation)

Answer 3

• Weigh an empty sample tube.
• Set up distillation apparatus.
• Add anti-bumping granules to organic solution in round-bottomed flask and connect to apparatus.
• Collect liquid impurities that come through condenser below 48°C in a small beaker.
• When temp reaches 48°C, collect liquid from condenser in the sample tube.
• Weigh sample tube and calculate mass of product formed.

Question 4

Key points of overall process

Answer 4

• Water bath or electric heater should be used to heat mixture if there are flammable substances present.
• Anti-bumping granules prevent large bubbles from forming and ensure the liquid doesn’t boil too vigorously (this would cause impurities to boil over into condenser, contaminating the product).
• Condenser should be tilted down to allow liquid to enter collection flask.
• Collection flask must not be sealed to condenser as this could cause the apparatus to crack.