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#Cobalt chloride system in weather indicator devices skin
#Cobalt chloride system in weather indicator devices trial

Starting with three tubes of violet-coloured solution, keep one tube as a control, and place another tube in the hot water (over 90 ☌).

If desired, show that these changes are reversible by adding concentrated HCl to the second test-tube and water to the third. Swirl to mix well as the liquids are added.

Keeping one tube as a control, use dropping pipettes to add water to the second tube and concentrated hydrochloric acid to the third until the colours change to pink and blue respectively.

Place about 2 cm depth of it in each of the six boiling tubes in two groups of three in suitable racks.

#Cobalt chloride system in weather indicator devices trial

If necessary, add more hydrochloric acid or water by trial and error to produce an ‘in-between’ violet coloured solution containing a mixture of the two cobalt ions.

Adding a more hydrochloric acid will produce a blue solution containing mainly 2–, while adding water will restore the pink colour. A violet-coloured solution should be formed.

Make the pink cobalt chloride solution up to 100 cm 3 with 60 cm 3 concentrated hydrochloric acid from a measuring cylinder.

A reddish-pink, approximately 0.4 M solution will be formed, which should be labelled as TOXIC.

Dissolve about 4 g of cobalt(II) chloride-6-water in 40 cm 3 of water in a beaker.

Boil a beaker of water and prepare a beaker of crushed ice and water.

Concentrated hydrochloric acid, HCl(aq), (CORROSIVE) – see to CLEAPSS Hazcard HC047a.

#Cobalt chloride system in weather indicator devices skin

As cobalt(II) chloride is a skin sensitiser, take care to avoid skin contact and wash hands well after use.

Cobalt(II) chloride–6–water, CoCl 2.6H 2O(s), (TOXIC, DANGEROUS FOR THE ENVIRONMENT) – see CLEAPSS Hazcard HC025.

Read our standard health and safety guidance.

Concentrated hydrochloric acid (CORROSIVE), 100 cm 3.Cobalt(II) chloride-6-water (TOXIC, DANGEROUS FOR THE ENVIRONMENT), 4.0 g.Rack for boiling tubes x1 or x2 (depending on capacity).The demonstration could also be adapted for use as a class experiment with suitable groups. For big groups the reactions should be scaled up, using larger containers such as measuring cylinders or beakers, to improve visibility. Pink cobalt species + chloride ions ⇌ Blue cobalt species + water moleculesĪ white background will help to show the colour changes to best effect. For the purposes of this discussion the equilibrium could adequately be represented by: If students are unfamiliar with the formulae of complex ions this may confuse the issue.

The demonstration can be used to introduce reversible reactions and chemical equilibrium or to illustrate Le Chatelier’s principle once these concepts have been established. The distinctive colours of the two cobalt(II) species in solution produce an attractive visual demonstration of a reversible reaction and the effect of concentration and temperature on the position of equilibrium. The colour changes accompanying the changes in equilibrium position are as predicted by Le Chatelier’s principle. This equilibrium can be disturbed by changing the chloride ion concentration or by changing the temperature.

The two different coloured Co(II) complex ions, 2+ and 2-, exist together in equilibrium in solution in the presence of chloride ions: RSC Yusuf Hamied Inspirational Science Programme.Introductory maths for higher education.The physics of restoration and conservation.