Anhydrous CoCl2 is blue; CoCl2•6H2O is red. When CoCl2•6H2O is heated and water is clearly being driven off, it becomes uniformly violet before turning blue. How can this be explained?

On losing 6 moles of water, cobalt chloride forms unstable violet-coloured ions, before generating its stable blue-coloured anhydrous form.

Explanation:

The hydrated cobalt chloride loses its 6 water of crystallization, then dissociates into ions: cobalt ions and chlorine ions that appear violet, and quickly combined to form the stable anhydrous Cobalt chloride with blue colour.

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.