The paper turns blue as anhydrous cobalt(II) chloride is formed. You can, if you are careful, dry the paper sufficiently just by holding it very close to a Bunsen flame.

Note: A desiccator is a piece of glassware with a close-fitting lid containing some substance which absorbs water under a perforated tray that holds whatever you want to dry. (The (II) is almost always missed out when you are talking about cobalt chloride paper.)įilter paper is dipped into cobalt(II) chloride solution and then dried, either by heating it in an oven at less than 100☌, or by leaving it in a desiccator for a longer time. The anhydrous form is used as cobalt chloride paper. If you add water to white anhydrous copper(II) sulfate, it turns blue again as it goes back to the hydrated form.Ĭobalt(II) chloride solution forms pink crystals, CoCl 2.6H 2O, and if this is heated gently it turns into blue anhydrous cobalt(II) chloride, CoCl 2. Using anhydrous copper(II) sulfate to test for water That is what is used to test for the presence of water. If you heat copper(II) sulfate crystals, they lose this water of crystallisation and you get white anhydrous copper(II) sulfate. There are 5 molecules of water of crystallisation: CuSO 4.5H 2O. The copper(II) sulfate is said to be hydrated. The familiar blue copper(II) sulfate crystals contain molecules of water bound into the crystal structure. Testing using anhydrous copper(II) sulfate This page looks at two common tests for the presence of water - anhydrous copper(II) sulfate and cobalt chloride paper.

Cobalt chloride and water equation