The Nature of Solutions

When $NaCl$ enters water, the following occurs: 1. The ionic bonds between $Na^+$ and $Cl^-$ begin to stretch as water molecules collide with the crystal. 2. Water molecules orient themselves: the partial negative oxygen atoms face the $Na^+$ ions, while the partial positive hydrogens face the $Cl^-$ ions. 3. These ion-dipole forces pull the ions into the solution, surrounding them with a 'hydration shell' of water.

Predict if Iodine ($I_2$) will dissolve better in Water ($H_2O$) or Carbon Tetrachloride ($CCl_4$): 1. Identify Polarity: $I_2$ is a diatomic molecule with equal sharing of electrons, so it is nonpolar. 2. Identify Solvent Polarity: $H_2O$ is bent and highly polar. $CCl_4$ is tetrahedral and symmetrical, making it nonpolar. 3. Apply Principle: $I_2$ (nonpolar) will be highly soluble in $CCl_4$ (nonpolar) but nearly insoluble in $H_2O$.

Consider a mystery salt where the energy to break the lattice ($\Delta H_1$) is $+800\text{ kJ/mol}$, the energy to separate the solvent ($\Delta H_2$) is $+100\text{ kJ/mol}$, and the energy released during hydration ($\Delta H_3$) is $-820\text{ kJ/mol}$. 1. Calculate $\Delta H_{soln} = 800 + 100 + (-820) = +80\text{ kJ/mol}$. 2. Since the result is positive, the process is endothermic. The solution will feel cold as it dissolves, and it may require heating to increase solubility.