Chapter 18 Notes I

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Chapter 18 Notes I

• Solutions Solubility
• Factors Affecting Solubility

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What is a Solution?

• A solution is the same thing as a homogeneous
  mixture (a mixture with the exact same
  composition throughout).

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Parts of a Solution

• Solute-the substance that is being dissolved in a
  solution
• Solvent-the substance in a solution that is being
  dissolved into.

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Solution of Two Liquids

• When two liquids are able to dissolve into each
  other, they are called miscible.
• If not, they are called immiscible.

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What can be dissolved?

• Remember the saying like dissolves like
• Polar solvents (like water) will only dissolve
  polar or ionic compounds.

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How does solvation occur?

• IMFs between polar molecule pull ions away from
  solid.

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Solubility

• Solubility is the amount of a substance that will
  dissolve into a quantity of solvent (at a given
  temperature)

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Solubility Rules

• There are several sets of rules that can help you
  to decide if a substance will be soluble in water
  or not.
• More on this later!!!

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Solubility, contd

• A solvent (like water, for example) can only hold
  so much of a solute.

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• If a solvent cannot hold any more of a solute (at
  that temperature) it is called saturated.
• If the solvent can hold more solute, it is called
  unsaturated.

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• Sometimes, a solution can hold more of a solute
  than it should theoretically hold. This type of
  solution is called supersaturated.
• How could this occur?

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Factors Affecting Solubility

• Generally, a substances solubility increases as
  temperature is increased. (This is not true of
  most gases).
• Why? The solvents particles are moving faster,
  and so they have more energy to break bonds.

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• In gases, pressure affects solubility. The
  higher the pressure, the more gas is soluble in a
  solvent.
• What is an example of this?

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Reading Solubility Charts
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Concentration

• Concentration-the amount of solute that is
  dissolved into a solvent
• Concentrated-when a solution has a high
  concentration of solute
• Dilute-when a solution has a low concentration of
  solute

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Concentration

• Concentration can be described in terms of weak
  or strong, concentrated or dilute, but
  these are both relative terms and can be
  subjective.

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So how do we measure concentration objectively?
There are lots of ways!
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Molarity

• Molarity is one way to measure concentration it
  is the number of moles of solute per liter of
  solution.
• The unit of molarity is mol/L, which can be
  abbreviated with an uppercase M.

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Practice Problem 1

• What is the molarity of a solution that contains
  0.15mol of MgCl2 in a 1.13L solution?

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Practice Problem 2

• A saline solution contains 0.020mol of NaCl in
  exactly 100mL of water. What is the molarity of
  this solution?

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Practice Problem 3

• How many moles of solute are present in a 1.5L
  sample of 0.24M Na2SO4?