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A reversible reaction of hydrated copper(II) sulfate

Class practical

Students remove the water of crystallisation from hydrated copper(II) sulfatebyheating. Condensing the vapour produced in asecond test-tube collects the water. The white anhydrous copper(II) sulfateis then rehydrated and the blue colour returns.

Lesson organisation

This experiment can be carried out in pairs by students. It should take no more than 30 - 40 minutes.

Apparatus Chemicals

Each group

will require:

EyeprotectionTest-tubes, 2

Delivery tube

(right-angled)Beaker, 250cm3

BunsenburnerClamp and

stand

Copper(II) sulfate(VI)-5-water(powdered),(HARMFUL, DANGEROUS FOR THEENVIRONMENT), about 5 gRefer to Health & Safety and Technicalnotes section below for additional

information.

Health & Safety and Technical notes

Read our standard health & safety guidance

Wear eye protection.

Copper(II) sulfate(VI)-5-water, CuSO4.5H2O(s), (HARMFUL, DANGEROUS FOR THE ENVIRONMENT) - see CLEAPSSHazcard.

Procedure

Unit 3. Air and Water

Syllabus Ref. 11.1

http://www.rsc.org/learn-chemistry/wiki/Substance:Copper(II)_sulfate_pentahydratehttp://www.rsc.org/learn-chemistry/wiki/Copper_sulfatehttp://www.rsc.org/learn-chemistry/wiki/Substance:Copper(II)_sulfate_pentahydratehttp://www.rsc.org/learn-chemistry/wiki/Substance:Copper(II)_sulfate_pentahydratehttp://www.rsc.org/learn-chemistry/wiki/Substance:Copper(II)_sulfate_pentahydratehttp://www.rsc.org/learn-chemistry/wiki/Substance:Copper(II)_sulfate_pentahydratehttp://www.rsc.org/learn-chemistry/wiki/Copper_sulfatehttp://www.rsc.org/learn-chemistry/wiki/Substance:Copper(II)_sulfate_pentahydrate

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aSet up the apparatus as shown (but without water in the recieving tube this is to be collected during the experiment), placingabout 5 g of powdered hydrated copper(II) sulfate in the test-tube. Make sure that the tube is clamped near the bung as shown.

bHeat the blue copper(II) sulfate until it has turned white. Move the flame along the length of the test-tube from time-to-time(avoiding the clamp) to prevent water condensing on the cooler regions and then running down on to the hot solid, possiblycracking the test-tube.

cAct quickly to prevent suck-back if the level of water collecting in the test-tube reaches the end of the delivery tube. Lift theclamp stand so that the delivery tube does not reach into the water in the test-tube.

dAllow the anhydrous copper(II) sulfate to cool back to room temperature.

eHolding the test-tube containing anhydrous copper(II) sulfate in one hand, pour thecollected water very slowly on to the white powder. What observations can you make?

fRecord any observations made during the heating process and when the water was poured back onto the anhydrous copper(II)sulfate.

Teaching notes

Ensure that the students have clamped the test-tube at the end nearest the bung before they start the experiment, otherwisethey will be heating the clamp as well as the test-tube.

Warn about and watch for suck-back. Demonstrate how to lift the entire clamp stand and apparatus.

The reaction involved is:

CuSO4.5H2O(s) (pale blue solid) CuSO4(s) ('dirty' white solid) + 5H2O(l)

Students should observe the colour change from pale blue to white and the change back to blue when water is added. The

colour change on adding water to anhydrous copper(II) sulfate has been used as a test for the presence of water in a liquid.

The more observant should notice that the addition of water to anhydrous copper(II) sulfate is exothermic, as the tube becomesnoticeably hot if the water is added very slowly. They should therefore conclude that the same quantity of energy is absorbedwhen the endothermic thermal decomposition takes place.

Perhaps in subsequent class discussion students could be asked why anhydrous copper(II) sulfate would not be a feasible fuelfor the future.

More able and older students might be asked to calculate the enthalpy change occurring during this process. They will need tofind out from a Data Book the standard enthalpies of formation for anhydrous and hydrated copper(II) sulfate, as well as that forwater.

Health & Safety checked, September 2014

Credits

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

7/24/2019 3. a Reversible Reaction of Hydrated Copper (II) Sulphate

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Nuffield Foundation and the Royal Society of Chemistry

Website

Wikipedia- this link gives information about the sources, uses and some reactions of copper(II) sulfate.

Page last updated October 2015