Which of the following species would you least expect to find in an aqueous solution of CaCl_2?

• A. CaCl_2 (s)
• B. Ca^{2+}
• C. H_2O
• D. Cl^{-}

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the nature of CaCl_2 in water. Calcium chloride (CaCl_2) is an ionic compound that typically dissociates completely in aqueous solution into its ions.
2. Step 2: Write the dissociation equation for CaCl_2 in water: \(\mathrm{CaCl_2 (s) \rightarrow Ca^{2+} (aq) + 2Cl^{-} (aq)}\).
3. Step 3: Recognize that in an aqueous solution, the solid form of CaCl_2 (s) is not expected to remain because it dissolves to form ions.
4. Step 4: Identify the species present in the solution: \(\mathrm{Ca^{2+}}\) ions, \(\mathrm{Cl^{-}}\) ions, and water molecules (\(\mathrm{H_2O}\)).
5. Step 5: Conclude that the species least expected to be found in the aqueous solution is the undissolved solid CaCl_2 (s), since it dissolves completely under normal conditions.