Class practical

The water from copper(II) sulfate solution is evaporated and some of it is condensed using simple apparatus.

Lesson organisation

This is a simple introduction to aqueous solutions. Water is the solvent and it is only water that distils off when a solution is boiled. Other coloured solutions can be used – ink was the traditional one, but few students will still use ink pens and fewer will be aware of ‘bottles of ink’.

This is quite a complicated apparatus to set up at what might be an early stage of the students’ chemical careers. It is recommended that the flasks are set up with delivery tubes for the students. The clamped apparatus should also be set up in advance for the students if there are any doubts about their ability to do this correctly.

Pupils must be standing up while practical work is being carried out.

More water can be condensed if a beaker of water is held round the collecting tube. This leads to the idea of a water condenser as a more efficient way of collecting the water. See experiment Recovering pure water from a solution using a water condenser.

The experiment will take about 20 minutes.

Apparatus Chemicals

Eye protection

Each group of students will need:

Conical flask, 100 cm3

Cork or bung with hole for delivery tube, to fit flask (see diagram)

Lengths of glass tubing, bent as shown in the diagram

Rubber connection tubing

Stand and two clamps

Tripod and gauze

Bunsen burner

Heat resistant mat

Test-tube

Measuring cylinder, 25 cm3

Copper(II) sulfate(VI) solution, about 0.5 M, 20 cm3 per group

Refer to Health & Safety and Technical notes section below for additional information.

Health & Safety and Technical notes

Read our standard health & safety guidance

Wear eye protection throughout.

Copper(II) sulfate(VI) solution, CuSO4(aq) - see CLEAPSS Hazcard and Recipe Book.

The solution left in the flask should be recycled by diluting after the experiment (the exact concentration is not important, but note that solutions of greater concentration than 1 mol dm–3should be labelled HARMFUL)

Procedure

a Set up a Bunsen burner on the base of a stand placed on a heat resistant mat.

b Place a tripod and gauze above the burner.

c Clamp a flask and a test tube as shown in the diagram.

d Collect 20 cm3 of copper sulfate solution and place it in the flask.

e Fix the tubing in position as in the diagram.

f Light the Bunsen and heat the flask gently with a small flame. Do not heat to dryness.

g Water should distil over into the collecting tube.

Teaching notes

The colourless liquid collected can be assumed to be water at this stage. The main point is that it is not blue. It may be possible to detect a darkening of the original solution, showing that it is becoming more concentrated.

Health & Safety checked, 2016

Credits

This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.

© Nuffield Foundation and the Royal Society of Chemistry

Website

Mike Curtis describes a good summary of ‘separation of mixtures’ including distillation, here (Common Entrance/KS3) and here (Primary/KS2).

Page last updated October 2015