Demonstration

When copper sulfate solution is boiled, pure water vapour is produced. This is then condensed in a water-cooled condenser to liquid water with a boiling point of 100°C.

Lesson organisation

(This experiment follows on from Recovering water from copper(II) sulfate solution)

It is best done as a demonstration which would take about 15 minutes (not including assembling the apparatus).

Apparatus Chemicals

Distillation flask (at least 100 cm3 capacity)

Water-cooled (Liebig) condenser and connection tubing to tap and sink

Corks or bungs to assemble apparatus (or use Quickfit apparatus)

Thermometer (-10° to +110 °C)

Stand, boss and clamp, 2

Bunsen burner

Tripod and gauze

Heat resistant mat

Beaker (100 cm3)

Anti-bumping granules (or pumice stone, or pieces of broken porcelain)

Copper(II) sulfate(VI) solution, 1 M (HARMFUL, DANGEROUS FOR THE ENVIRONMENT), 30 cm3

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.

Copper(II) sulfate(VI) solution, CuSO4(aq), (HARMFUL at this concentration) - see CLEAPSS Hazcard and CLEAPSS Recipe Book. Copper(II) sulfate(VI) is DANGEROUS FOR THE ENVIRONMENT - recycle the copper sulfate after the demonstration by mixing it with the water that has collected in the beaker.

Procedure

a Set up the apparatus as shown in the diagram, with about 30 cm3 copper(II) sulfate(VI) solution (and a few anti-bumping granules) in the flask.

b Turn on the cooling water. Only a slow flow through the apparatus is needed.

c Heat the copper sulfate solution until it boils, then adjust the flame to keep it boiling gently.

d Read the thermometer as water begins to condense on it and then as the vapour moves down into the condenser.

e Use a beaker to collect the water that runs out of the condenser.

Teaching notes

As in experiment  Recovering water from copper(II) sulfate solution , an important point is that the blue solution boils to give the colourless solvent (water). In this experiment, the boiling point of the solvent can be measured and should be steady and close to 100°C (depending on the accuracy of the thermometer, and the pressure). This is by far the best test for pure water. The use of cobalt(II) chloride paper or anhydrous copper(II) sulfate only indicates the presence of water.

Evaporation occurs at any temperature. Boiling occurs when the vapour pressure of the liquid equals the pressure of the atmosphere. At this temperature, small bubbles (which contain water vapour, not air) are formed in the liquid and rise to the surface. Anti-bumping granules help these bubbles to form. If the granules are not there, the liquid may ‘bump’, i.e. boil violently.

Point out to the students the mode of action of the water condenser. If water enters at the bottom and comes out at the top, only a slow flow through the condenser is needed.

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

Weblinks

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