Chapter 5_ Section 3 by dffhrtcv3


									                Chapter 7: Solutions

                                          Air is a Gaseous
Sodium Chloride Liquid

                         Section 1:
                  Solutions VS Mixtures
                     What is a mixture?
• Mixtures of different substances exist all around us.
   – Many of these mixtures are invisible, and we never notice
   – However, some mixtures can easily be identified.
                     What is a mixture?
• All matter is either a pure substance or a mixture of other
   – Definition: pure substance – matter that has a fixed chemical
• For example:
  Water is a pure substance.        Kool-Aid is a mixture of
      It is ALWAYS H2O.            water and other substances.
                       Types of Mixtures
• Mixtures can be categorized into two groups:
  – Heterogeneous and Homogeneous
   – Definition: heterogeneous mixture – a mixture made of
     visibly different substances.
      • The particles in a het. Mixture are not spread evenly.
      • Orange juice with pulp is an example of a heterogeneous mixture.
Heterogeneous Mixture

                          Clear Orange

                        Orange Juice
         Heterogeneous Mixtures

                                  fragments make
                                    up this rock.

This rock is a heterogeneous mixture.
                  Homogeneous Mixtures
• Homogeneous mixtures look the same all over.
  – Definition: homogeneous mixture – a mixture in which the
    particles are spread evenly.
  – Sweet tea is an example of a homogenous mixture.
  – There are several different substances (tea, water, and sugar)
    but you cannot see them. The tea looks uniform (the same)
+   +

The tea looks the
same throughout
  the pitcher.
• We can call homogeneous mixtures by another name:
  – Definition: solution - a homogenous mixture of 2 or more
    substances that are evenly dispersed.
• Many solutions are formed by dissolving one substance into
  another substance.

   – These tablets are dissolving
     in the water to form a
                      What is in a Solution?
• It is important to know what makes up a solution.
• All solutions are made of solutes and solvents.

   – Definition: solute - a substance that dissolves into another substance.

   – Definition: solvent - a substance that a solute is dissolved into.
• For example:
  – When you stir sugar into water, the sugar dissolves.
  – The water is the solvent.
  – The sugar is the solute.

                 +                      =
  Solute                   Solvent                  Solution
                 The Universal Solvent
• Water is very good at dissolving things.
  – Water is known as “The Universal Solvent”
                  Other types of Solutions
• Not all solutions contain water!
• Other states of matter can be solutions.
   – Gases & Solids can form solutions also.

   – Air is an example of a gaseous solution.

   – Air is composed of lots of different gases that we cannot see.
                          Metal Alloys
• 2 or more solids can form solutions also.
   – Metal alloys are homogenous mixtures that contain a metal
     mixed with another substance.
   – Some examples are:
      • Steel – iron and carbon
      • Brass – copper and zinc
      • Bronze – copper and tin
                         Metal Alloys
• In order to make an alloy, the metals must be melted.
   – While melted, the metals are mixed to form a solution.


 Tin                  Copper
      Chapter 7: Solutions

Section 2: How Substances Dissolve
                    How do things dissolve?
• Water can dissolve ionic compounds because of its structure.
   – The electrons in the hydrogen atoms are pulled toward the oxygen

   – This gives the oxygen atom a slight negative charge.

   – The hydrogen atoms gain a slight positive charge.
    The Water Molecule

H                        H

                 Polar Compound

• Because water’s + and – charges are not
  spread out evenly, it becomes “polar”.

  – Definition: polar compound – a molecule
    that has a positive side and a negative side.

    •Because water is a polar compound, it is a
     good solvent.
                   Like dissolves Like
– In chemistry, a rule of thumb is that “like dissolves like.”
– Water is a polar compound, so it can dissolve other polar

– If water cannot dissolve a substance, then that substance is
             Nonpolar Compound

– Definition: nonpolar compound – a
  compound that has no charge on its

  •Nonpolar compounds can only dissolve other
   nonpolar substances.

  •Example – oil-based paint will not dissolve in
   water. A nonpolar solvent must be used.
  Polar vs. Nonpolar

Oil is Nonpolar

 Water is Polar

They cannot mix.
              The Dissolving Process
• We have all seen solutes dissolve into solvents
• And we all *probably* know some ways to
  speed up the process.
             The Dissolving Process

• Making a solute smaller makes it dissolve
  – By crushing up a solute, you increase the
    surface area.
                             Crushed Salt

                 Rock Salt
                The Dissolving Process
• Stirring or shaking will make a solute dissolve faster.
              The Dissolving Process

• Increasing the solvent’s temperature will
  make the solute dissolve faster.

                     Which one will
                     Dissolve sugar
            The Dissolving Process: Gases

• Did you know that liquids can dissolve gases?

• Fish and other aquatic life breath oxygen that
  has dissolved into water.

• Liquids dissolve gases best
  when they are cold.
            The Dissolving Process: Gases

• Don’t believe it? Well, consider this…

  – Which makes a louder “whoosh” sound when
    opened… a hot soda or a cold one?
• The amount of solute dissolved in a
  solvent affects its concentration.

  – Think of concentration as being how
    “strong” a solution is.

  – Definition: concentration – the amount of a
    substance in a certain amount of solution.
• “Concentrated” substances have lots of solute.
• “Diluted” substances only have a little solute.
             Saturated / Unsaturated

• When a solvent can no longer hold any
  more solute, we called it “saturated”.

  – Definition: saturated solution – a solution
    that cannot dissolve any more of a given

  – Definition: unsaturated – a solution that
    CAN hold more solute.
                 Super Saturated

• Sometimes, a solvent can be made to
  hold more solute than normal.
  – The solution is called “supersaturated”.

  – Definition: supersaturated – a solution that
    has more solute than normal.
                        Super Saturated
• Supersaturated solutions are unstable.
   – The extra solute can “fall out” at any time.

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