Final answer:
The significance of [Ca²⁺] is related to the solubility of calcium propionate in solution. It indicates the concentration of calcium ions in a saturated solution where the solubility limit has been reached.
Step-by-step explanation:
The significance of [Ca²⁺], which stands for the concentration of calcium ions, in the context of a solution of calcium propionate, the calcium salt of propionic acid, is related to the solubility of the salt in the solution. The concentration given at 0.26 M reflects the amount of calcium ions present in a saturated solution, which is a solution where no more solute can dissolve.
When propionic acid reacts with calcium hydroxide, the balanced equation is:
2 CH₃CH₂CO₂H + Ca(OH)₂ → Ca(CH₃CH₂CO₂)₂ + 2 H₂O,
indicating the formation of aqueous calcium propionate and water. The solubility product constant (Ksp) is relevant here as solubility is dependent on factors such as pH, common ions present, and temperature.