The Demonstration

Take the pink cobalt chloride solution and make it up to 100cm with concentrated hydrochloric acid using a measuring cylinder. A violet solution will be formed. Adding more hydrochloric acid will produce a blue solution containing , while adding water will restore the pink colour.

By trial and error produce an 'in between' violet coloured solution containing the two cobalt chloride ions and place about 2cm depth of it in each of the six boiling tubes. Place these on the bench in two groups of three.

1. Effect of concentration

Keeping one tube as a control, add water to one tube and concentrated hydrochloric acid to the other using dropping pipettes. If desired, show that these changes aer reversible.


2. Effect of Temperature

Keeping one tube as a control, place another tube in hot water (over 90). It will go blue. Put the third tube in the ice/water mixture. It will go pink. If desired, shoe that these chenges are reversible.