Cobalt(II) chloride, a blue solid, can absorb water from the air to form cobalt(II) chloride hexahydrate, a pink solid. The equilibrium is so sensitive to moisture in the air that CoCl₂ is used as a humidity indicator.
a. Write a balanced equation for the equilibrium. Be sure to include water as a reactant to produce the hexahydrate.

Verified step by step guidance

1. Identify the chemical formula for cobalt(II) chloride, which is CoCl₂, and the formula for its hexahydrate, which is CoCl₂·6H₂O.
2. Recognize that the reaction involves the absorption of water (H₂O) from the air to form the hexahydrate. This means water is a reactant in the equation.
3. Write the unbalanced equation: CoCl₂ (s) + H₂O (g) ⇌ CoCl₂·6H₂O (s).
4. Balance the equation by ensuring the number of water molecules matches the hexahydrate formula. Since the hexahydrate contains 6 water molecules, the balanced equation becomes: CoCl₂ (s) + 6H₂O (g) ⇌ CoCl₂·6H₂O (s).
5. Verify that the equation is balanced by checking that the number of each type of atom (Co, Cl, H, O) is the same on both sides of the equation.

Key Concepts

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In the case of cobalt(II) chloride, the equilibrium between the anhydrous form and the hydrated form is influenced by external factors like humidity, demonstrating how environmental conditions can shift the balance of a chemical reaction.

Hydration Reaction

A hydration reaction involves the addition of water to a substance, leading to the formation of a hydrate. For cobalt(II) chloride, the reaction with water results in the formation of cobalt(II) chloride hexahydrate, which is a solid that contains water molecules integrated into its crystal structure, changing its color from blue to pink.

Balanced Chemical Equation

A balanced chemical equation represents a chemical reaction with equal numbers of each type of atom on both sides of the equation. For the hydration of cobalt(II) chloride, the balanced equation must reflect the conversion of CoCl₂ and water into CoCl₂·6H₂O, ensuring that the number of cobalt, chlorine, and hydrogen atoms is conserved throughout the reaction.