Ch 14: Solutions

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Ch 14 Solutions

• Solutions are homogeneous mixtures (solute
  solvent).
• Solute is the dissolved substance.
• Seems to disappear in the solvent.
• Solvent is the substance in which the solute
  dissolves.
• Does not appear to change state.
• Aqueous solutions
• Have water as the solvent.
• Water is called the universal solvent because it
  dissolves so many substances.
• Metal solutions (one metal dissolved in another)
  are called alloys (ex steel, brass, bronze).
• See table 14.1 for all types of solutions

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14.1 Solubility

• When one substance (the solute) dissolves in
  another (the solvent) it is said to be soluble.
• Ex salt and ethanol are both soluble in water
• When one substance does not dissolve in another
  it is said to be insoluble.
• Ex oil is insoluble in water
• When a solute and solvent have the same state
  (gas, liquid, or solid), the solvent is the
  component present in the highest percentage.
• Metal solutions (one metal dissolved in another)
  are called alloys.
• Ionic Compounds
• Dissociate into ions when dissolved in water
• Polar water molecules interact with positive and
  negative ions to dissolve the compound (fig 14.1,
  14.2)
• ions surrounded by water molecules are hydrated

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• Covalent Compounds
• Polar covalent compounds have polar groups that
  tend to be soluble in water.
• Ethanol (a liquid) or sucrose (table sugar), for
  example, have polar O-H bonds that interact with
  water to enhance solubility.
• See fig 14.3, 14.4
• Nonpolar covalent compounds have molecules that
  do not form attractions to water molecules
  because all their bonds are essentially
  non-polar, which prevents them from being soluble
  in water.
• Petroleum products or vegetable oil molecules are
  examples.
• See figs 14.5, 14.6

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• Molecules that are similar in structure tend to
  form solutions like dissolves like
• A given solvent dissolves solutes that have
  polarities similar to its own.
• Water (a polar molecule) dissolves most polar
  solutes (liquids or solids).
• Non-polar solvents dissolve nonpolar solutes.
  Gasoline, for example, dissolves in oil since
  they are both nonpolar compounds. However,
  neither gasoline nor oil will dissolve in water
  because water is polar.
• Gases are always soluble in each other.

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14.2 Solution Composition

• Concentration amount of solute in a given
  amount of solution.
• A concentrated solution has a high proportion of
  solute to solution.
• A dilute solution has a low proportion of solute
  to solution.
• A saturated solution contains the maximum amount
  of solute that will dissolve in the solvent at a
  particular temperature. (The higher the
  temperature the greater the saturation.)
• An unsaturated solution contains less solute than
  the saturation limit.
• A supersaturated solution contains more solute
  than the saturation limit.
• Unstable the solute easily precipitates out of
  solution.

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14.3 Solution Composition Mass Percent

• Mass percent is an expression of the mass of
  solute present in a given mass of solution.
• Mass Percent (grams of solute mass of
  solution) x 100
• Remember, the mass of the solution is the sum of
  the masses of the solute and the solvent.
• See examples 14.1, 14.2

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14.4 Solution Composition Molarity

• Describes a solution in terms of concentration,
  or the amount of solute in a given volume.
• Molarity (M) moles of solute per 1 liter of
  solution.
• A standard solution is a solution whose
  concentration is accurately known. See Fig 14.7
  for preparation.
• Molarity calculations See examples 14.3, 14,4,
  14.6, 14.7 in text
• Calculate molarity
• Calculate moles/mass of solute
• Calculate volume of solution

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14.5 Dilution

• Dilution is adding solvent to decrease the
  concentration of a solution. See Fig 14.8 and
  example 14.8.
• The amount of solute stays the same, but the
  solute concentration decreases due to the added
  solvent.
• Dilution Formula M1 x V1 M2x V2
• M1V1 before dilution M2V2 after dilution
• Since molarity is defined in terms of liters,
  change any volume in milliliters to liters to
  solve dilution problems.
• A standard solution is one whose concentration is
  accurately known. It can be used to make
  dilutions.
• Examples