5 - Distillation of a reaction product

What is distillation?

• A technique where a liquid is heated to create a vapour which is cooled by a condenser, causing the gas to condense into a liquid & drip into a separate flask

• The species separate due to different volatilities & boiling points

What equipment is used for distillation?

• Pear-shaped/round-bottomed flask

• Liebig condenser

• Thermometer

• Water bath

• Collecting vessel (test tube in a beaker of ice & cold water)

• Anti-bumping granules

Butanone can be made by oxidising butan-2-ol with a mixture of sodium dichromate (VI) & sulfuric acid. Describe how you would then remove the butanone from the reaction mixture (6 marks)

Use distillation, as butanone has a lower boiling point than butan-2-ol. Butanone has Van der Waals forces & permanent dipole-dipole forces, whereas butan-2-ol has both & hydrogen bonding:

1. Transfer the reaction to a round-bottomed flask with a side-arm & add anti-bumping granules

2. Clamp the round-bottomed flask over a thermostatically controlled water bath (safer than a Bunsen burner’s naked flame for flammable alcohol)

3. Add a bung with a thermometer attached, which sits at the height of the side-arm. Ensure the bung is fully sealed to the flask to allow maximum collection of butanone

4. Attach the Liebig condenser to the side arm & apply heat using the water bath

5. Collect the distillate when the thermometer shows the boiling point of butanone in a collecting vessel (test tube in a beaker of ice & cold water)

Why are anti-bumping granules used in distillation?

• Prevents large bubbles from forming & allows smoother boiling

• Ensures the liquid doesn’t boil too vigorously, causing upwards splashing in the flask & so the mixture doesn’t jump into the condenser

Why must water enter at the lowest point & leave at the highest point in the Liebig condenser?

Ensures the condenser is completely filled with cold water (prevents backflow of water) & maximises the heat transfer for condensation (otherwise butanone would not condense)

What are some common practical hazards & risks in the laboratory?

Bunsen burner → burns

• keep away from flammable chemicals & from the edge of the desk

Chemicals → may be an irritant/corrosive (causing irritation to skin, eyes & lungs), toxic or flammable

• handle with care & while wearing gloves

• wear eye protection & keep away from edge of the desk & an open flame. don’t ingest

Glassware (e.g. beakers, test tubes) → may break & cut you

• handle with care & keep away from the edge of the desk