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Solubility Crystallize Solute + Solvent  Solution Dissolve Unsaturated Solution – Additional solute will still dissolve Saturated Solution – No additional solute will dissolve, equilibrium between solution and undissolved solute

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Solubility

Crystallize

Solute + Solvent  Solution

Dissolve

  • Unsaturated Solution – Additional solute will still dissolve

  • Saturated Solution – No additional solute will dissolve, equilibrium between solution and undissolved solute

  • Supersaturated Solution – Beyond the point of saturation


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Salt Solubility and Health

  • Sodium urate is formed from uric acid, a natural chemical in the body. Uric acid can also come from foods.

  • Uric acid in normal amounts remains dissolved in the blood, easily passes through the kidneys and leaves the body as waste. Uric acid in high amounts, however, makes a person more likely to develop gout.

    • Uric acid crystals deposit in the joints

  • The amount of uric acid in your blood can change depending on:

    • What you eat: red meats and internal organs (such as liver and kidneys), some shellfish and anchovies

    • Your overall health

    • How much alcohol you drink

    • What medicines you are taking

    • Sudden illnesses

    • The kidneys' ability to rid the body of uric acid (heredity).


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Solubility

Crystallize

Solute + Solvent  Solution

Dissolve

  • Factors Affecting Solubility

    • Energy Requirements

      • Solvent-Solute interactions (like dissolves like)

      • Temperature Effects

    • Pressure Effects (Henry’s Law)


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The Solution Process

Energy Changes and Solution Formation


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The Solution Process

Energy Changes and Solution Formation

CaCl2 example

NH4Cl example


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The Solution Process

Energy Changes and Solution Formation

  • Breaking attractive intermolecular forces is always endothermic.

  • Forming attractive intermolecular forces is always exothermic.

  • To determine whether Hsoln is positive or negative, we consider the strengths of all solute-solute and solute-solvent interactions:

    • H1 and H2 are both positive.

    • H3 is always negative.

    • It is possible to have either H3 > (H1 + H2) or H3 < (H1 + H2).


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The Solution Process

Energy Changes and Solution Formation

  • “Rule”: polar solvents dissolve polar solutes. Non-polar solvents dissolve non-polar solutes. Why?

    • If Hsoln is too endothermic a solution will not form.

    • NaCl in gasoline: the ion-dipole forces are very weak because gasoline is non-polar. Therefore, the ion-dipole forces do not compensate for the separation of ions (loss of ion-ion interactions).

    • Water in octane: water has strong H-bonds. There are no attractive forces between water and octane to compensate for the lost H-bonds when water molecules separate.


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Salt Solubility Examples

  • Some salts have very low solubility in water and reach saturation right away

These salts are often referred to as “Insoluble” salts

Ion-ion interaction are too strong to be separated by water


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Temperature Affects on Solubility

  • Most solids increase solubility in a liquid with increasing temperature

  • Most gases decrease solubility in a liquid with increasing temperature


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Pressure Affects on Solubility

  • Solubility of liquids and solids not greatly affected by pressure

  • Solubility of gases greatly affected by pressure (Henry’s Law)

    • Increase pressure = Increase solubility

    • Coca-cola example



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Bends and Scuba Diving“Henry’s Law in Action”

  • Pressure on the body increases at the divers goes deeper

  • Increased pressure = increased gas in blood

  • Air is mostly nitrogen so more nitrogen than normal dissolved in our blood

  • As the diver ascends, the gases come out (pressure decreases)

    • Fast ascends = lots of bubbles (BAD for our organs and joints!)


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Altitude Illness- Mountain Sickness (Form of Hypoxia)

  • Most likely to be affected are mountain climbers, pilots and persons living at high altitudes above 8,000 feet.

  • High altitude = low pressure = low oxygen concentration dissolved in blood

  • In a healthy person at sea level, blood is 95% saturated with oxygen. At 18,000 feet it is only 71% saturated.


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Ways of Expressing Concentration

  • All methods involve quantifying amount of solute per amount of solvent (or solution).

  • Generally amounts are measures are masses, moles or liters.

  • Qualitatively solutions are dilute or concentrated.

  • Definitions:


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Ways of Expressing Concentration

  • Parts per million (ppm) can be expressed as 1 mg of solute per kilogram of solution.

  • Parts per billion (ppb) are 1 g of solute per kilogram of solution.

  • Proof by conversion


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Ways of Expressing Concentration

Mole Fraction, Molarity, and Molality


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Ways of Expressing Concentration

Mole Fraction, Molarity, and Molality

  • Converting between molarity (M) and molality (m) requires density of solution

    • L of solutions to kg of solution

    • kg of solution = kg solvent + kg solute

moles of solute

kg of solvent

molality =


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Colligative Properties

  • Colligative properties depend on quantity of solute molecules.

    • Freezing point depression

    • Boiling point elevation


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Lowering the Vapor Pressure

  • Non-volatile solvents reduce the ability of the surface solvent molecules to escape the liquid.

  • Therefore, vapor pressure is lowered.

  • The amount of vapor pressure lowering depends on the amount of solute.


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Boiling-Point Elevation

  • Non-volatile solute lowers the vapor pressure.

  • Higher Temperature needed to achieve 1 atm of vapor pressure

    Freezing-Point Depression

  • Non-volatile solute lowers the vapor pressure, and shift triple point to lower temperature

  • Lower temperature of triple point produces lower phase change temperature


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Colligative Properties

Boiling-Point Elevation

  • At 1 atm (normal boiling point of pure liquid) there is a lower vapor pressure of the solution. Therefore, a higher temperature is required to reach a vapor pressure of 1 atm for the solution (Tb).

  • Molal boiling-point-elevation constant, Kb, expresses how much Tb changes with molality of particles, m:


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Colligative Properties

Freezing-Point Depression

  • The solution freezes at a lower temperature (Tf) than the pure solvent.

  • Decrease in freezing point (Tf) is directly proportional to molality of particles (Kfis the molal freezing-point-depression constant):