![]() ![]() The change in colour from blue to pink of the cobalt complexes here has been the basis of cobalt chloride indicator papers for the detection of the presence of water. If desired, show that the changes are reversible by swapping over the two test-tubes. Put the third tube in the ice/water mixture. 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. 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. ![]() Causes severe skin burns and eye damage may cause respiratory irritation, see CLEAPSS Hazcard HC047a. Concentrated hydrochloric acid, HCl(aq), CORROSIVE, IRRITANT.Take particular care to avoid skin contact and wash hands well after use. ![]() Take care to avoid allowing small volumes of soution to dry out on glassware/lab surfaces wipe up immediately with a damp cloth or paper towel avoid raising dust. Harmful if swallowed may cuase an allergic skin reaction may cause allergy or asthma symptoms or breathing diffculties if inhaled suspected of causing genetic defects may cause cancer by inhalation may damage fertitlity very toxic to aquatic life with long lasting effects, see CLEAPSS Hazcard HC025.
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