Concentration II Factors Affecting It Chapter 12 Unit 10

Solubility Soluble / Insoluble: Ability of a solute to be dissolved in a solvent. In reality, everything is slightly soluble. Atoms & molecules are so small (and there are so many of them), that a tiny amount will always dissolve even with insoluble substances.

Solubility of Liquids Miscible / Immiscible: For Liquids, describes ability to mix “Like Dissolves Like” Hydrophilic & hydrophobic e.g. Oil and water are immiscible. Remember, ionic & compounds with hydrogen-bonding are hydrophilic. Must have the same polarity!

Effects of T Solubility generally increases with temperature. Solubility of gases in liquids decreases with increasing temperature.

Effects of P Little effect on condensed phases (solids & liquids) Great effect on solubility of gases. Henry’s Law: P = k H C The amount of gas that can be dissolved is directly proportional to the pressure of the gas above the solution. P 1 /C 1 = P 2 /C 2

Henry’s Law in Action Very little CO 2 dissolves in 100 g H 2 O at 20 °C & normal pressures (P CO2 ~ 39 Pa) A can of soda is pressurized with about 3 atm (300,000 Pa) of CO g CO 2 will dissolve in 100 g H 2 O at that pressure. When you open a soda, the pressure drops and the CO 2 comes bubbling out!

Describing Concentration Dilute: (adj) A solution containing a low amount of solute. Dilute: (v) To decrease the concentration. Concentrated: A solution containing a high amount of solute.

Describing Concentration II Unsaturated: A solution that can dissolve more of the solute. Saturated: A solution that cannot dissolve any more of the solute. A saturated solution will have some visible solute on the bottom of the container.

Describing Concentration III Supersaturated: A solution that holds more than the maximum amount of solute. Most often by heating a solution to dissolve excess solute, then carefully cooling. Must be extremely clean & still. Impurities & agitation can cause the excess solute to fall out of solution (quickly).

Dissociation When ionic compounds dissolve in water, they dissociate into ions. Ions can conduct electricity. Called Electrolytes Nonionic substances cannot dissociate. Do not conduct electricity Called Nonelectrolytes

Making Solutions Volumes are not additive! 50 mL H 2 O + 50 mL Ethanol ≠ 100 mL In order to make solutions: 1. Add solute to small amount of solvent 2. Stir to dissolve. 3. Add additional solvent until the total volume reaches the desired level.

T (°C) g solute per 100 g H 2 O Concentrations (g/100g H 2 O) under the line are considered unsaturated. Solutions with concentrations on the line are saturated. Solutions that have been carefully prepared to have concentrations above the line are supersaturated.