This resource provide instruction for preparing your own cobalt chloride indicator papers. The papers are used to test for the presence of water. They will change from blue to pink in the presence of water.

Teacher notes

Cobalt(II) chloride is an inorganic compound of cobalt and chlorine, with the formula CoCl2. It is usually supplied as the hexahydrate CoCl2·6H2O. The hexahydrate is deep purple in color, whereas the anhydrous form is pale blue. Cobalt chloride paper is useful because the hydration/dehydration reaction occurs readily making the paper an indicator for water .

Apparatus Chemicals

Filter paper

Drying oven set at 100oC


Hexahydrate cobalt(II) chloride CoCl2·6H2O (TOXIC, DANGEROUS FOR THE ENVIRONMENT, SENSITISER ) 5 g

Water 100 cm3

Refer to Health & Safety and Technical notes section below for additional information.

Health & Safety and Technical notes

Read our standard health & safety guidance

Cobalt chloride is TOXIC and DANGEROUS FOR THE ENVIRONMENT and May cause sensitisation. The indicator papers should be handled as little as possible and hands washed after use.

Refer to CLEAPSS Hazcard and CLEAPSS Recipe Book.

Making cobalt chloride papers


a Dissolve 5 g of hydrated cobalt(II) chloride in 100 cm3 of water (solution is TOXIC).

b Soak filter paper in this solution, drain and dry in an oven (set at no more that 100°C), so that it is a definite blue colour.

c The filter paper can be cut into small strips and stored in a desiccator with dry silica gel.

Health & Safety checked, August 2016


This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.

© Nuffield Foundation and the Royal Society of Chemistry

Page last updated October 2015