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Solubility and Henry’s Law

Solubility and Henry’s Law. Chapter 12 continued. Solubility. There is usually a limit to the solubility of one substance in another gases are always soluble in each other two liquids that are mutually soluble are said to be miscible alcohol and water are miscible

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Solubility and Henry’s Law

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  1. Solubility and Henry’s Law Chapter 12 continued

  2. Solubility • There is usually a limit to the solubility of one substance in another • gases are alwayssoluble in each other • two liquids that are mutually soluble are said to be miscible • alcohol and water are miscible • oil and water are immiscible • The maximum amount of solute that can be dissolved in a given amount of solvent is called the solubility • The solubility of one substance in another varies with temperature and pressure Tro: Chemistry: A Molecular Approach, 2/e

  3. Will It Dissolve? • Chemist’s Rule of Thumb – Like Dissolves Like • A chemical will dissolve in a solvent if it has a similar structure to the solvent • when the solvent and solute structures are similar, the solvent molecules will attract the solute particles at least as well as the solute particles are attracted to each other • Polar molecules and ionic compounds will be more soluble in polar solvents • Nonpolar molecules will be more soluble in nonpolar solvents Tro: Chemistry: A Molecular Approach, 2/e

  4. Solubility Limit • A solution that has the solute and solvent in dynamic equilibrium is said to be saturated • if you add more solute it will not dissolve • the saturation concentration depends on the temperature • and pressure of gases • A solution that has less solute than saturation is said to be unsaturated • more solute will dissolve at this temperature • A solution that has more solute than saturation is said to be supersaturated Tro: Chemistry: A Molecular Approach, 2/e

  5. How Can You Make a Solvent Hold More Solute Than It Is Able To? • Solutions can be made saturated at non-room conditions – then allowed to come to room conditions slowly • For some solutes, instead of coming out of solution when the conditions change, they get stuck in-between the solvent molecules and the solution becomes supersaturated • Supersaturated solutions are unstable and lose all the solute above saturation when disturbed • e.g. shaking a carbonated beverage Tro: Chemistry: A Molecular Approach, 2/e

  6. Temperature Dependence of Solubility of Gases in Water • Gases generally have lower solubility in water than ionic or polar covalent solids because most are nonpolar molecules • gases with high solubility usually are actually reacting with water • For all gases, the solubility of the gas decreases as the temperature increases • the DHsolution is exothermic because you do not need to overcome solute–solute attractions Tro: Chemistry: A Molecular Approach, 2/e

  7. Temperature Dependence of Gas Solubility in Water (g/100 g H2O) Tro: Chemistry: A Molecular Approach, 2/e

  8. Tro: Chemistry: A Molecular Approach, 2/e

  9. Pressure Dependence of Solubility of Gases in Water • The larger the partial pressure of a gas in contact with a liquid, the more soluble the gas is in the liquid Tro: Chemistry: A Molecular Approach, 2/e

  10. Henry’s Law • The solubility of a gas (Sgas) is directly proportional to its partial pressure, (Pgas) Sgas = kHPgas • kH is called the Henry’s Law Constant Tro: Chemistry: A Molecular Approach, 2/e

  11. Relationship between Partial Pressure and Solubility of a Gas Tro: Chemistry: A Molecular Approach, 2/e

  12. Tro: Chemistry: A Molecular Approach, 2/e

  13. persrst Tro: Chemistry: A Molecular Approach, 2/e

  14. [CO2] P Example 12.2: What pressure of CO2 is required to keep the [CO2] = 0.12 M in soda at 25 °C? Given: Find: S = [CO2] = 0.12 M, P of CO2, atm Conceptual Plan: Relationships: S = kHP, kH = 3.4 x 10−2 M/atm Solve: Check: the unit is correct, the pressure higher than 1 atm meets our expectation from general experience Tro: Chemistry: A Molecular Approach, 2/e

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