Solubility and Concentration

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Solubility and Concentration

• ChemistryMrs. Coyle

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Part I Solubility

• The ability of a solute to dissolve in a solvent.
• Expressed as g solute/100g H2O
• or g solute/100mL H2O

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Soluble

• Soluble a solute that has appreciable
  solubility.

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Miscible

• Substances that dissolve in each other.

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Solubility Curves
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Precipitate solute that comes out of solution.

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Types of Solutions

• Saturated contains the maximum amount of solute
  that can be dissolved at the given conditions of
  T and P.
• Unsaturated contains less than the saturated
  amount of solute.
• Supersaturated contains more than the saturated
  amount of solute by dissolving at higher temp and
  then cooling.

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A supersaturated solution crystallizes after a
seed crystal is introduced.
http//www.chem.ufl.edu/itl/2045/change/C12F11.GI
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Rates of Solution

• Does every candy you eat take the same time to
  dissolve?

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Factors affecting the rate of dissolving

• Surface Area
• Stirring
• Temperature (average kinetic energy)

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Factors Affecting Solubility

• Temperature (affects solid, liquid and gaseous
  solutes)
• Pressure (affects gaseous solutes)

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Effect of temperature on solubility of gases.

• ExampleCompare the amount of oxygen dissolved
  in the waters of the arctic ocean
• to the amount of oxygen dissolved in warm
  tropical waters.

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Effect of temperature on solubility of solids.

• Example Can you dissolve more sugar in warm
  water or in cold water?

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Solubility Curves
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Effect of Pressure on solubility of solids.

• Negligible.

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Effect of Pressure on solubility of gases.

• Henrys Law the amount of gas dissolved in a
  solution is directly proportional to the pressure
  of the gas above the solution.
• The higher the pressure the higher the solubility
  of the gas.

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Effect of Pressure on solubility of gases.
http//www.chem.ufl.edu/itl/2045/lectures/lec_i.h
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Example

• An unopened bottle of soda has a pressure of
  5atm above the liquid, so the concentration of
  CO2 in the soda is high.
• Compare that to a pressure of 1 atm above the
  liquid when the bottle has been opened.

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Part II Concentration

• A measure of the amount of solute dissolved in
  the solution.
• Molarity (M)
• Molality (m)
• Mole Fraction (x)
• Percent by Mass ()

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Part II

• Concentration

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Molarity

• A unit of concentration of a solution expressed
  in moles solute per liter of solution. (Note 1L
  1 dm3)

Moles of Solute
Molarity (M)
Liters of Solution
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Why Molarity ?

• http//www.chem.ucla.edu/gchemlab/volumetric_soln
  _conc.jpg

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Steps involved in the preparation of a standard
aqueous solution
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Process of making 500 mL of a1.00 M acetic acid
solution
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Ex. 1 Molarity

• What is the molarity of a solution of 8g NaOH in
  100mL of solution?
• Answer 2M NaOH

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Ex. 2 Molarity

• How many grams of NaOH are contained in 2L of a
  3M NaOH solution?
• Answer 240g NaOH

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Making Dilutions

• Moles SoluteM1V1M2V2
• M molarity
• V volume

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Ex. 3 Dilutions

• How many milliliters of 2.00M MgSO4 solution
  must be diluted with water to prepare 100.00 mL
  of 0.400M MgSO4?
• Answer 20.0mL

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Percent by Mass

• by mass Mass of solute x 100 Mass
  of solution

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Percent by Volume

• by volume Volume of solute x 100
  Volume of solution

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Part III Molality and Mole Fraction
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Molality

• Moles of Solute per kilogram of Solvent

Molality (m) moles solute kg
solvent
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Mole Fraction

• xsolute Moles of solute Moles of
  solution
• xsolvent Moles of solvent
  Moles of solution
• xsolute xsolvent 1