Cobalt chloride is a blue-violet crystalline solid that is soluble in water. When dissolved in water, it dissociates into cobalt ions (Co2+) and chloride ions (Cl-). Cobalt ions can undergo a colour change when they are exposed to different ligands (molecules or ions that can bind to metal ions).
Potassium dichromate is a bright orange-red crystalline solid that is also soluble in water. When dissolved in water, it dissociates into potassium ions (K+) and dichromate ions (Cr2O72-). Dichromate ions can also undergo a colour change when they are exposed to different ligands.
HydroChrome works by combining cobalt chloride and potassium dichromate in a specific ratio and dissolving them in water. The resulting solution is initially yellow-orange in colour due to the presence of dichromate ions. As the solution is heated, the cobalt ions react with the dichromate ions to form a hydrated complex that turns the solution blue-green. This colour change is reversible and the solution can be turned back to its original yellow-orange colour by cooling it down.
The exact chemical reactions that occur in HydroChrome are complex and involve the formation of various intermediate compounds. However, the overall effect is a colour change that is dependent on temperature, which makes it a useful tool for demonstrating chemical reactions and teaching about colour changes in chemistry.
