Part I: Solubility, Factors Affecting Solubility

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Part I Solubility, Factors Affecting
Solubility  

• CHM 102
• Friday, July 6th

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Practice Solubility and Saturation

• If the solubility of sodium acetate is 65 g per
  100 mL H2O at 100oC, then will any sodium acetate
  remain undissolved if we pour 140 g of sodium
  acetate into 200 mL of water? What is the
  condition of the solution (saturated.unsaturated)
  ?

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Practice Solubility and Saturation

• If the solubility of potassium chloride is
• 42.1 g per 100 mL H2O at 100oC, then will any
  sodium acetate remain undissolved if we pour 81 g
  of sodium acetate into
• 150 mL of water? What is the condition of the
  solution (saturated.unsaturated)? How much more
  (if any) could we dissolve into the solution?

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Factors Affecting Solubility

• Solute-Solvent Interactions
• Pressure Effects (dissolving gases)
• Temperature Effects (for both gaseous and solid
  solutes)

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Solute-Solvent Interactions

• The formation of solute-solvent interactions is
  the only exothermic contribution to the heat of
  solution.
• Exothermic (negative DH) values for the
  solute-solvent interaction term points towards a
  solution process that is spontaneous.
• So the stronger the solute-solvent interactions,
  the more exothermic the overall solution process
  will be.

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Solute-Solvent Interactions

• This idea breaks into the classic like dissolves
  like principle.
• Water, the universal solvent is really not
  entirely universal. Water is polar, and will
  tend to dissolve polar and ionic substances, but
  will not dissolve nonpolar substances (i.e. oil)
  readily.

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NaCl Dissolves in Water
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Example Water and Alcohol

• Do water and alcohol mix? Whats an example?
  These two liquids are said to be miscible. If
  they didnt, theyd be termed imiscible.

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Practice Alcohols and Solvent-Solute
Interactions

• Which is more soluble in water, ethanol (C2H3OH),
  butanol (C4H9OH), or hexanol
• (C6H13OH)? Why?

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Pressure Effects

• When dissolving a gas in water, Henrys Law shows
  that when pressure of a gas above a solution goes
  up, its solubility in the solution increases
• S k P
• S is solubility, k is Henrys gas constant (which
  is solute and solvent AND temperature dependent).

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Practice Pressure Effects

• What is the solubility of carbon dioxide in coke
  if the soda is at 25oC and the pressure of CO2
  above the solution is 0.025 atm? (henrys law
  constant is 3.110-2 mol/Latm)
• S k P

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More Practice Pressure Effects

• What is the henrys law constant for CO2 at 298 K
  when the solubility of carbon dioxide is known to
  be 0.12 mol/L when the pressure of CO2 above the
  liquid is 4.0 atm?
• S k P

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Temperature Effects-Gases

• When dissolving gases, the solubility of a gas in
  a substance tends to go DOWN as the temperature
  goes up.
• Think of a cold soda sitting outside open on a
  hot day. What happens?

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Temperature Effects-Solids

• When dissolving solids, the solubility of a solid
  in a substance tends to go UP as the temperature
  goes up.
• Think of making sweet tea or kool-aid. If you
  want the sugar buzz of your life, you dont
  dissolve sugar in cold water, you dissolve it in
  HOT water. The solubility of the sugar goes up
  as the temperature gets hotter.

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Part II Ways of Expressing Concentration

• CHM 102
• Friday, July 6th

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Ways of Expressing Concentration

• Mass Percentage
• Parts-per-million (ppm)
• Parts-per-billion (ppb)
• Mole Fraction
• Molarity
• Molality

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Mass Percentage

• Mass Percentage is just as it sounds. It is the
  percent of what component youre interested in
  compared to the whole
• Practice What is the mass percent sugar in a
  2.07 kg solution with 350 g of sugar in it?
  

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Parts-per-million (and billion)

• Parts-per-million and parts-per-billion are often
  used for very dilute solutions to express
  concentration
• If 16.5 mg of NaCl is dissolved in 1.6 kg of
  water, what is the concentration of NaCl in ppm?
  ppb?

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More Practice ppm and ppb

• What is the ppm of Na if 24.2 mg of NaCl is
  added to 1.78 kg of water? (hint use mass
  percentage first!) ppb of Na?

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Mole Fraction

• Mole fraction is also just as it sounds. It is
  the number of moles of what component youre
  interested in compared to the total moles
• Practice If youve got 73 g of HCl in 162 g of
  water,
• what is the mole fraction of HCl in the solution?
  

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Molarity and Molality

• Do not get these two mixed up! VERY COMMON
  MISTAKE!
• The following two definitions for molarity and
  molality should be memorized!!!
• Molarity is given in moles of solute per liter of
  solution.
• Molality is given in moles of solute per kilogram
  of solvent.

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Molarity

• What is the concentration of sodium carbonate (MW
  106 g/mol) in molarity when 26.5 g Na2CO3(s) is
  dissolved to a total volume of 2 L? What is the
  molarity of sodium ions, K?

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Molality

• What is the concentration of sodium carbonate (MW
  106 g/mol) in molality when 53 g Na2CO3(s) is
  dissolved in 1896 g of DI water?

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Moving Between Concentrations

• An aqueous solution of NaCl is 10 sodium
  chloride by mass. What the concentration of NaCl
  in molarity?
• 50.0 g of sucrose (MW ) is dissolved in 1375 g
  of ethanol (MW , density 0.79 g/mL). What is
  the molarity of this solution? What is the mass
  percent sucrose in the solution?