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Solubility

Solubility. Some Solubility Terms. Liquids that mix in all proportions are called miscible . When there is a dynamic equilibrium between an undissolved solute and a solution, the solution is saturated .

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Solubility

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  1. Solubility

  2. Some Solubility Terms • Liquids that mix in all proportions are called miscible. • When there is a dynamic equilibrium between an undissolved solute and a solution, the solution is saturated. • The concentration of the solute in a saturated solution is the solubility of the solute. • A solution which contains less solute than can be held at equilibrium is unsaturated.

  3. Formation of a Saturated Solution Eventually, the rates of dissolving and of crystallization are equal; no more solute appears to dissolve. Solid begins to dissolve Longer standing does not change the amount of dissolved solute. As solid dissolves, some dissolved solute begins to crystallize.

  4. Solubility As A FunctionOf Temperature • About 95% of all ionic compounds have aqueous solubilities that increase significantly with increasing temperature. • Most of the remainder have solubilities that change little with temperature (A very few have solubilities that decrease with increasing temperature). • If solubility increases with temperature, a hot, saturated solution may cool without precipitation of the excess solute. This creates a supersaturated solution.

  5. A Supersaturated Solution …until all of the excess solute has precipitated. A single “seed crystal” of solute is added. Solute immediately begins to crystallize…

  6. Some Solubility Curves

  7. Selective Crystallization When KNO3(s) is crystallized from an aqueous solution of KNO3 containing CuSO4 as an impurity, CuSO4 (blue) remains in the solution. KNO3 crystallized from a hot, saturated solution, is virtually pure.

  8. The Solubilities Of Gases • Most gases become less soluble in liquids as the temperature increases . • At a constant temperature, the solubility (C) of a gas is directly proportional to the pressure of the gas (Pgas) in equilibrium with the solution. Pgas= kC The value of k depends on the particular gas and the solvent. • The effect of pressure on the solubility of a gas is known as Henry’s Law.

  9. Effect of Temperature on Solubility of Gases Thermal pollution: as water gets warmer (from industrial use for cooling), less oxygen dissolves, and fish no longer thrive.

  10. Pressure and Solubility of Gases Higher partial pressure means: more molecules of gas per unit volume… …thus more frequent collisions of gas molecules with the surface… …giving a higher concentration of dissolved gas.

  11. Gas Pressure and Solubility in Water Solubilities of gases such as HCl and CO2 do increase with pressure…but the increase isn’t linear. Henry’s Law isn’t valid for gases that react with water (HCl, CO2)

  12. Practice • The solubility of methane, the chief component of Bunsen burner gas, in water at 20oC and 1 atmosphere of pressure is 0.025 g/L.  What will be its solubility at 1.4 atm and 20oC?

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