CH. 12: Solutions Part 1

Characteristics of Solutions Homogeneous mixtures containing 2 or more substances Solute: the substance that dissolves (salt) Solvent: the substance doing the dissolving (water or alcohol) Water is the most common solvent Soluble vs. insoluble Miscible vs. immiscible

2. Solvation Solute and solvent particles must mix Solvation is the process of surrounding a solute with solvent particles. Solvation in water is called hydration.

Dissolution vs reaction dry Ni(s) + HCl(aq) NiCl2(aq) + H2(g) NiCl2(s) Dissolution is a physical change—you can get back the original solute by evaporating the solvent. If you can’t, the substance didn’t dissolve, it reacted.

3. Solubility Refers to the maximum amount of a solute that will dissolve in a given amount of solvent at a specific temperature and pressure. Usually expressed in grams of solute per 100 grams of solvent. Example: ammonium chloride at 20oC is 36.4 g/100 g of water

4. Solution Types Supersaturated Solution

Degree of saturation Unsaturated Solution Less than the maximum amount of solute for that temperature is dissolved in the solvent. No solid remains in flask.

Degree of saturation Supersaturated Solvent holds more solute than is normally possible at that temperature. These solutions are unstable; crystallization can often be stimulated by adding a “seed crystal” or scratching the side of the flask.

Degree of saturation Saturated solution Solvent holds as much solute as is possible at that temperature. Undissolved solid remains in flask. Dissolved solute is in dynamic equilibrium with solid solute particles.

5. Factors that Affect Solubility Temperature: Substances tend to be more soluble at higher temperatures Pressure: Solubility of a gas increases as the pressure above the solution increases. Think shaking a soda can.