why does cobalt chloride strip turn pink or blue?
It indicates the amount of water present in the sample, by going back and forth between a hydrated and anhydrous form. Each has a different color.
http://en.wikipedia.org/wiki/Cobalt(II)_chloride
1. Two dogs are fighting over a 0.5 kg bone. The larger dog pulls on the bone in one direction with a force of 40 N. The smaller dog pulls in the opposite direction with a force of 36 N. What is the net force on the bone?
Cobalt chloride is a chemical compound that exists in two forms, hydrated and anhydrous. The hydrated form of cobalt chloride is pink, while the anhydrous form is blue. The color change occurs because cobalt chloride is a pH indicator, meaning it can change its color depending on the acidity or alkalinity of a solution. Here's how it works:
1. Hydrated cobalt chloride (CoCl2·6H2O) is pink because it contains water molecules within its crystal structure. When the compound is dissolved in water, it forms a complex ion called the hexaaquacobalt(II) ion ([Co(H2O)6]2+), which appears pink.
2. If the pink cobalt chloride strip is heated, the water molecules are driven off, and the anhydrous cobalt chloride (CoCl2) is formed.
3. When anhydrous cobalt chloride is exposed to moisture, it readily absorbs water molecules from the atmosphere, converting back to the hydrated form. This process is known as hydration or hydrolysis.
4. In the presence of moisture, the hydrated cobalt chloride reverses the dehydration process and recovers its pink color.
5. However, if anhydrous cobalt chloride is exposed to higher humidity or water vapor, it forms a new compound called cobalt chloride hexahydrate (CoCl2·6H2O). This compound has a different crystal structure and appears blue.
To summarize, when cobalt chloride is hydrated, it appears pink due to the water molecules within its structure. When it loses water through heating, it becomes anhydrous and changes to a blue color. Upon exposure to moisture again, it absorbs water and reverts to the hydrated form, thus turning pink again.