Chapter 11: Solutions

1
Chapter 11 Solutions

• Solution a homogeneous mixture
• What is a mixture?
• Contains more than one pure substance
• Can be separated into its components by physical
  means
• Does not have a fixed composition
• Homogeneous properties are uniform throughout
• Question Can you think of a nonhomogeneous
  mixture?

2
Solvents and Solutes

• Solvent the component of a solution present in
  the greatest amount
• Solute all lesser components of a solution
• Phases or states of matter in solutions
• Liquid in liquid
• Solid in liquid
• Gas in liquid
• Gas in gas
• Other combinations

3
The Solution Process

• Ex. NaCl(s) ? Na(aq) Cl (aq)
• Unsaturated Solution
• Rate of dissolving gt Rate of precipitation
• All of solute dissolves.
• Saturated Solution
• Rate of dissolving Rate of precipitation
• Dissolved and undissolved solute are in
  equilibrium.
• Supersaturated Solution an unstable condition.
  Any disturbance will lead to spontaneous
  precipitation and a return to equilibrium.

4
Concentration Units

• Concentration How much solute?
• Amount of solute / Amount of solution or
• Amount of solute / Amount of solvent
• Hint Always label the numerator and
  denominator with the terms solute or solvent.
• Molarity, M
• M (mol/L) No. moles solute / No. liters
  solution

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• Mole Fraction, ?
• Let A solvent and B solute
• Then ?B no. moles B / total no. of moles in
  solution
• Note ?A ?B ?i 1
• Molality, m
• m (mol/kg) no. moles solute / no. kilograms
  solvent
• Mass or weight percent, (w/w)
• B(w/w) (mass of solute / mass of solution) x
  100

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• What about the density (?) of the solution?
• ? (g/mL) mass of solution / volume of solution
• Now we know all of the important relationships.
• Ex. Commercial concentrated HCl is 37.3(w/w)
  HCl in water. The density of this solution is
  1.18 g/mL.
• Calculate the molarity, molality, and mole
  fraction of HCl in this solution.
• What information do we know about the solution?
• There are 37.3 g of HCl for every 100 g of
  solution.
• There are 1.18 g of solution for every 1 mL of
  solution.

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• Molarity mols HCl / L soln
• How do we find mols of HCl?
• To convert grams to moles, use the molar mass.
• How do we find liters of solution?
• To convert mass of solution to volume of
  solution, use the density.
• 12.1 M (mols HCl / L soln)

37.3 g HCl 100 g soln
1 mol HCl 36.46 g HCl
1.18 g soln 1 mL soln
1000 mL soln 1 L soln
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• Molality mols HCl / kg H2O
• How do we find the mass of H2O?
• We know the relative mass of solute and mass of
  solution from the mass percent.
• 100 g of solution contains 37.3 g of HCl
• Thus, 100.0 g soln 37.3 g HCl 62.7 g H2O
• 16.3 m (mol HCl / kg H2O)

37.3 g HCL 62.7 g H2O
1 mol HCl 36.46 g HCl
1000 g H2O 1 kg H2O
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• Mole Fraction mol HCl / (mol HCl mol H2O)
• 37.3 g HCl (1mol HCl / 36.46 g HCl) 1.02
  mol HCl
• 62.7 g H2O (1 mol H2O/18.02 g H2O) 3.48 mol
  H2O
• ?HCl 1.02 mol HCl /(1.02 3.48 mol total)
  0.227