ch302 notes - CH302 Chapter 17: PROPERTIES OF SOLUTIONS...

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CH302 Chapter 17: PROPERTIES OF SOLUTIONS Part 2 Effect of Pressure on Solubility solid or liquid solute in a liquid solvent: Pressure has little or no effect. gaseous solute in a liquid solvent: Pressure has a large effect! Henry's Law P gas = k H χ gas Typical values for k H are shown in Table 17.3 Amount of gas that dissolves in a solution is directly proportional to the pressure of the gas above the solution! Dissolving or Reacting? Some gases enhance their solubility via reaction with water: Henry's Law is then less accurate HCl (g) Æ H + (aq) + Cl - (aq) CO 2(g) + CO 3 2- (aq) + H 2 O (l) 2HCO 3 - (aq) This reaction can go backwards: when it does, in a solution with Ca 2+ ions present, scale (CaCO 3 ) forms. Effect of Temperature on Solubility of Solids in Water: Not easy to predict! This is only a GENERALIZATION and is not always true: Exothermic dissolution: solubility decreases as T increases : Endothermic dissolution: solubility increases as T increases : Δ H solution is positive for dissolving sugar in water, does this make sense ? Dissolution Rates: Dissolution is faster for -Large surface area (e.g., powdered sugar vs. sugar cubes) -Higher temperatures Do not confuse SPEED with apparent solubility! Fig. 17.5: The only way to know exactly how solubility varies with T is via experiment! Effect of Temperature on Solubility of Gases in Water Fig. 17.6: Gases become LESS soluble as T increases! Thermal Pollution At 1atm, O 2 has a limited solubility; enough to keep fish alive! Water is used in power stations as a coolant. It may not contain contaminants BUT: If discharged at too high T, it cannot dissolve enough O 2 to support aquatic life Also is less dense so floats on top of the other water. .blocking normal O 2 uptake Vapor Pressures of Solutions: VP of the pure solvent bigger than VP of solution Fig 17.8: Pure solvent keeps vaporizing- but cannot reach equilibrium, because the solution
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This note was uploaded on 05/01/2009 for the course CH 52410 taught by Professor Sutcliffe during the Spring '09 term at University of Texas.

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ch302 notes - CH302 Chapter 17: PROPERTIES OF SOLUTIONS...

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