Answer :
Final answer:
Two solutions are isotonic if they have the same osmotic pressure, which depends on the total concentration of dissolved particles. Ionic compounds dissociate in water, altering the number of particles and thus the isotonicity of the solutions compared to non-dissociating solutes.
Explanation:
The concept in question is the isotonicity of different aqueous solutions at the same temperature. Isotonic solutions are those that have the same osmotic pressure, usually due to having the same concentration of solute particles. To determine whether two solutions are isotonic, we use the concept of freezing point depression and the dissociation of ionic compounds in water.
For instance, a 1M aqueous solution of NaCl dissociates into 2 moles of ions (1 mole Na+ and 1 mole Cl-), doubling the number of particles and affecting the colligative properties such as freezing point depression and osmotic pressure. A 1M solution of NaCl would therefore not be isotonic with a 2M solution of urea, which does not dissociate into ions. Similarly, for a 1M CaCl2 solution, it would dissociate into 3 moles of ions (1 mole Ca2+ and 2 moles Cl-) per mole of solute, resulting in a different osmotic pressure than a 1.5M solution of KCl, which would only provide 2 moles of ions per mole of solute.
