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Concentration II

Concentration II. Factors Affecting It. Solubility. Soluble / Insoluble: Ability of a solute to be dissolved in a solvent. In reality, everything is slightly soluble.

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Concentration II

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  1. Concentration II Factors Affecting It

  2. 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.

  3. 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.

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

  5. Effects of P • Little effect on condensed phases (solids & liquids) • Great effect on solubility of gases. • Henry’s Law: P = kHC • The amount of gas that can be dissolved is directly proportional to the pressure of the gas above the solution. • P1/C1 = P2/C2

  6. Henry’s Law in Action • Very little CO2 dissolves in 100 g H2O at 20 °C & normal pressures (PCO2~ 39 Pa) • A can of soda is pressurized with about 3 atm (300,000 Pa) of CO2. • 0.45 g CO2 will dissolve in 100 g H2O at that pressure. • When you open a soda, the pressure drops and the CO2 comes bubbling out!

  7. 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.

  8. 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.

  9. 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).

  10. 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

  11. Making Solutions • Volumes are not additive! • 50 mL H2O + 50 mL Ethanol ≠ 100 mL • In order to make solutions: • Add solute to small amount of solvent • Stir to dissolve. • Add additional solvent until the total volume reaches the desired level.

  12. Concentrations (g/100g H2O) 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. g solute per 100 g H2O T (°C)

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