Final answer:
Direct measurement of ionized Ca²⁺ is not done due to the high ionization energy required for removal of additional electrons from calcium atoms, making the process energetically unfavorable and complex. Indirect methods are preferred for practicality and due to the stable nature of ionic lattices formed by Ca²⁺ ions.
Step-by-step explanation:
The reason why ionized Ca²⁺ is not typically measured directly is due to the complexity and energy involved in the process. In chemistry, removing electrons from an atom requires ionization energy especially when dealing with elements such as calcium. After removing the first two electrons from calcium to get Ca²⁺ a third electron would have to be removed from an orbital closer to the nucleus, which greatly increases the ionization energy required. This process is endothermic and energetically unfavorable in the formation of compounds like CaCl3, which is why compounds such as CaCl₂ are more common due to the stability provided by the ionic lattice formed between the Ca²⁺ ions and Cl⁻ ions.
Moreover, removing more electrons from an atom with the same number of protons results in a disproportionately higher ionization energy; hence, the direct measurement of ionized Ca²⁺ in solutions is complex making indirect methods like titration analysis more practical. In aqueous solutions, Ca²⁺ may act as a spectator ion that does not participate in the chemical reaction further indicating the preference for indirect measurement techniques.