Transcript Chapter 23

Chapter 23
SOLUTIONS
What is a solution?
• Solution—a mixture that has the same
composition, color, density, and even taste
throughout
• Ex: hummingbird food-has both sugar and
red dye in the solution
• Solute—the substance being dissolved in a
solution
• Solvent—the substance doing the dissolving
in the solution
More on solutions
• Solutions can be composed of any
combination of solids, liquids and gases
• Ex: air is a solution of 78% nitrogen, 20%
oxygen and small amts of other gases such as
argon, carbon dioxide and hydrogen
• Alloys-solid solutions
– They are made by melting the metal solute and
solvent together
Dissolving
• Dissolving solids in liquids
– Ex: hummingbird food, fruit drinks/sports drinks
– How do solids dissolve in water?
• Water molecules are constantly moving
• Water molecules are also polar, and solute molecules are
polar as well
Ex: pg. 709/Figure 3
How it Happens
• Water molecules cluster around solute
molecules w/negative ends attracted to
positive ends of the solute
• Water molecules pull the solute molecules into
solution
• Water molecules and the solute molecules mix
evenly, forming a solution
Dissolving Liquids and Gases
• When a gas dissolves in a liquid, particles of
liquids and gases move much more freely
than do particles of solids
• When gases dissolve in gases or when liquids
dissolve in liquids, this movement spreads
solutes evenly throughout the solvent
Dissolving Solids in Solids
• In order to mix to solids, ,
– Ex: two solid metals are first melted
and then mixed together.
– In this liquid state, the metal atoms
can spread out evenly and will remain
mixed when cooled
Rate of Dissolving
• Stirring-a solutionspeeds up dissolving
because it brings more fresh solvent into
contact w/more solute
• Grinding lg. crystals (solids) into smaller ones
speeds of dissolving also
• Temperature—increasing temperature of the
solvent always speeds up the dissolving rate
– Ex: hot chocolate
Gases in Solution
• When you shake an opened bottle of soda, it
bubbles up and may squirt out
• Shaking or pouring a solution of a gas in a
liquid causes gas to come out of solution
• If you want to dissolve more gas in a liquid,
you can increase the pressure of that gas over
the liquid
– Ex: soft drinks (carbon dioxide pressure)
Temperature
• Another way to increase the amount of gas
that dissolves in a liquid is to cool the liquid
• Ex: even more carbon dioxide will bubble out
of a soft drink as it gets warmer
Section 2—Dissolving w/out Water
• **Water can’t dissolve some solutes because
of its polarity
• **However, non-polar materials have no
separated positive and negative areas.
• **Non-polar materials do not attract polar
materials, which means they do not attract
water
• SO:**Non-polar materials DO NOT dissolve in
water
Non-polar Solutes
• Ex: vinegar and oil salad dressing has two
layers—bottom layer is vinegar, and top layer
is salad oil
• Equal distribution of electrons means the
molecules of oil have no separate positive and
negative areas, so they will not mix with
water.
Versatile Alcohol
• Some substances form solutions w/polar
and non-polar solutes
• They have molecules with both polar and nonpolar ends
• The polar end dissolves polar substances, and
vice versa.
• Ex: ethanol dissolves iodine and water
Useful Non-Polar Solvents
• Mineral Oil—used as a solvent to remove
candle wax from glass, or metal or bubble
gum from some surfaces
• Oil-based paints have materials dissolved in
oils, so a non-polar solvent must be used to
thin or remove them
• Dry cleaners use non-polar solvents when
removing oily stains
Toxicity
• Although non-polar solvents have many uses,
they have some drawbacks, too.____
1. Many are flammable
2. Some are toxic (skin/inhalation, etc)
You must always be careful when handling
these materials, and use a well ventilated area
How Soap Works
• The oils on human skin and hair keep them
from drying out, but the oils can also attract
and hold dirt
• Oily dirt is a nonpolar mixture, so e must
wash with soap to get rid of dirt
• SOAP-has both non-polar and polar properties
• Soap is used to remove dirt from skin, hair, or
fabric by attaching oily dirt to the hydrocarbon
end and water to the ionic end
Polarity and Vitamins
• Having the right kinds and amounts of
vitamins is important for your health
• B vitamins and vitamin C are polar
compounds=they dissolve in water (water
soluble)
• You must replace these vitamins by eating
enough of the foods that contain them or by
taking vitamin supplements
Fat-Soluble Vitamins
• Some vitamins such as vitamin A are nonpolar and can dissolve in fat
• They do not wash away with water and are
not easily eliminated by the body
• They can accumulate in tissues, which can
become toxic
• Other ex: Vitamins D, E and K
Section 3—Solubility
• Solubility-the max amt. of a solute that can be
dissolved in a given amt. of solvent at a given
temp.
• The amount of a substance that can dissolve
in a solvent depends on the nature of these
substances
– Explanation of how to determine solubility-pg. 718
Concentration
• Ex: You add 1 tsp. of lemon juice to a glass
of water
• Your friend adds 4 tsps. Of lemon juice to
another glass the same size
• You could say your friend’s lemonade is
concentrated, and your glass is dilute because
your friend’s drink now has more lemon flavor
than yours
More on Concentration/Dilution
• A concentrated solution is one in which a
large amount of solute is dissolved in the
solvent
• A dilute solution is one that has a small
amount of solute in the solvent
• To measure concentration precisely it is
sometimes given as a percent
– (% fruit juice, etc.)
Types of Solutions
• Saturated solution-a solution that
contains all the solute it can hold at a
given temperature.
– (if heated, however, it could hold
more)
– SO: as the temp of a liquid solvent
increases, the amt of solid solute it
can dissolve also increases
Types of Solutions
• Unsaturated solution—a solution that
can dissolve more solute at a given
temperature
• Each time a saturated solution is heated
to a higher temp, it becomes
unsaturated
Types of Solutions
• Supersaturated Solution-a solution that
contains more solute than a saturated one at
the same temperature
• Ex: if a seed crystal of sodium acetate is
dropped into the supersaturated solution,
excess sodium acetate crystallizes out
Solution Energy
• Some portable heat packs use crystallization
from supersaturated solutions to produce heat
• After crystallization, the heat pack can be
reused by heating it to again dissolve all the
solute.
Section 4-Particles in Solution
• Ions-the charged particles in the fluids that
are in and around all the cells in your body
• Electrolytes—the compounds that produce
solutions of ions that conduct electricity in
water
– there are both strong (soldium chloride) and weak
electroylytes (acetic acid)
– Nonelectrolytes—substances that form no ions
in water and cannot conduct electricity
– Ex: ethyl alcohol and sucrose
How Ionic Solutions Form
• To form ions, the molecules must be broken
apart in such a way that the atoms take on a
charge
• Ionization—the process of forming ions so
that molecules are broken apart and atoms
take on a charge
• Dissociation—the process in which an ionic
solid, such as sodium chloride, separates into
its positive and negative ions
– Ex: pg. 724
Effects of Solute Particles
• All solute particles-polar and nonpolar,
electrolyte and nonelectrolyte, affect the
physical properties of the solvent, such as its
freezing point and its boiling point
• Ex: adding antifreeze to water in a car
radiator lowers the freezing point of the
radiator fluid
– (sugar and salt would do the same thing)
• The effect that a solute has on the freezing pt
or boiling pt of a solvent depends on the
number of solute particles in solution, NOT on
the chemical nature of the particles
• (it’s not a chemical reaction)
Lowering Freezing Point
• Adding antifreeze to a solvent lowers the
freezing point of the solvent
• How much the freezing point goes down
depends upon how many solute particles you
add.
Raising Boiling Point
• Antifreeze also raises the boiling point of the
water
• The amount the boiling point is raised
depends upon the number solute molecules
present
• Solute particles interfere w/evaporation of
solvent particles
More on Raising the Boiling Point
• More energy is needed for the
solvent particles to escape from the
liquid surface, so the boiling point
of the solution will be higher than
the boiling point of solvent alone
Car Radiators
• When a car radiator contains water only, no
antifreeze, the following occurs:
• Some of the molecules on the surface will
vaporize and the number of molecules that do
vaporize depends upon the temp of the
solvent
• When the solvent heats up, the molecules
move faster, and particles vaporize
• Finally when pressure of water vapor equals
atmospheric pressure, water BOILS