Unit 4: Solutions

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Unit 4 Solutions

• (Chemists have Solutions!)

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Definitions

• Solution Homogenous mixture of two or more
  substances in a single phase
• Solvent is the component of a solution that
  exists in the greatest quantity.
• Solute is the component of a solution that
  exists in the smaller quantity.
• Saturated Solution A solvent is said to be
  saturated with a solute, when no more solute will
  dissolve into it.
• Unsaturated Solution is one in which more solute
  can be dissolved

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Definitions

• Soluble a solute is soluble in a solvent if the
  solute and the solvent mix to form a homogenous
  mixture.
• Insoluble a solute is said to be insoluble in a
  solvent if less than 0.1 moles of the solute will
  dissolve in a liter of solution
• Solubility is the maximum amount of a given
  solute that dissolves in a given solvent at a
  given temperature. I.e., when measuring the
  solubility of a system it must be for a saturated
  solution.

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Units of Solubility

• Solubility is the maximum concentration of a
  solute in a solvent for a given temperature.
  Units of solubility are
• Grams(solute)/liter of solution
• Moles(solute)/liter of solution (M, molarity)

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Determining Solubility

• Must prepare a saturated solution
• Use an xs amount of solute (goal is to have some
  un-dissolved solute separate from the solution)
• Mix thoroughly and let sit over night at a
  constant temperature
• Pipette a known amount of the saturated solution
  (25.00 ml) into a pre-weighed weigh boat
• Evaporate solution to dryness (remove solvent)
• Determine the weight of the solute
• Calculate solubility in grams/liter (convert to
  mol/L if required

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Properties of Solutions

• Conductivity is a measure of how well a solution
  conducts electricity. ( for a solution to conduct
  electricity, it must contained charged particles,
  I.e., IONS)
• pH the pH of a solution is a measure of how much
  H ions are in solution, the lower the pH the
  more H ions there are present , the Higher the
  pH the less H ions there are. Neutral water has
  a pH of 7.0 ( at 25 C.)

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Dissolving Vs. Dissociating

• Dissociating is when an Ionic compound breaks
  down into its ions in solution
• Dissolving is when a covalent compound is
  absorbed by the solution, however it keeps its
  same chemical composition.

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The Theory of Solubility

• Polar solvents will dissociate ionic compounds
  and dissolve polar covalent compounds
• Non-polar solvents will dissolve only non-polar
  covalent compounds.

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What is Polarity?

• A compound is said to be polar if it processes a
  net permanent dipole moment that do not cancel
  each other out.
• Permanent dipole moments occur in covalent
  molecules where bonds exists between atoms with
  different electron-negativity.
• A Net permanent dipole occurs when all the
  dipoles in a molecule do not cancel each other
  out.

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Molecular Shapes and Polarity
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Importance of Polarity

• Polarity effects the solubility of a solute in a
  given solution
• Polarity effects the phase a pure compound will
  likely be in
• Polarity effects the shape of large molecules
  such as proteins

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Intermolecular ForcesVs.Intramolecular Forces

• Intramolecular forces are the forces internal to
  the molecule. They are responsible for holding
  the atoms in the molecule together.
• Intermolecular Forces are the forces between
  molecules
• Dipole/Dipole interactions (polarity)
• Hydrogen bonding
• London forces