Chapter 15
Section 15.2
Homogeneous Aqueous Systems
Think-Pair-Share
O Explain why you must be extremely careful
when using electricity near a swimming pool.
Solutions
O Aqueous Solution-Water that contains a
dissolved substance.
O 2 Parts to a solution:
O Present in the smallest amount - Solute
O Solvent - Present in the larger amount
O Solvent dissolves the Solute.
Solutions
O Are Solvents and Solutes found in the liquid
state only?
O Gas Solutions
O The air we breathe- Oxygen and Nitrogen
O Carbon Dioxide mixed with your liquid soda
O Solid Solutions
O Nickel Coin- Copper and Nickel
O Sterling Silver- Silver and Copper
O Can you name any?
Solutions
O Homogeneous mixtures- nothing settles out
when left standing
O Solute particles are very…very small.
O Less than 1nm = 10 -9 m
O What would happen if we tried to filter a
homogeneous solution through filter paper?
Could you separate the solute from the
solvent?
Solutions
O Substances that dissolve most readily in
water are…
O Ionic Compounds
O Polar Covalent Compounds
O Polar molecules dissolve in Polar molecules.
O Nonpolar covalent molecules such as oils,
fuels, and grease dissolve in Nonpolar
covalent molecules.
The Solution Process
O A water molecule is polar, with a partial
negative charge on the oxygen atom and
partial positive charges on the hydrogen
atoms.
O As individual solute ions break away from
the crystal, the negatively and positively
charged ions become surrounded by solvent
molecules and the ionic crystal dissolves.
The Solution Process
O The process by which the positive and
negative ions of an ionic solid become
surrounded by solvent molecules is called
solvation.
O This relationship can
be summed up in the
expression “like
dissolves like.”
O Why is the oil and
water not mixing?
O Can oil and gasoline
mix?
Electrolytes
O An electrolyte is a compound that conducts
an electric current when it is in an aqueous
solution or in the molten state.
O All ionic compounds are electrolytes
because they dissociate into ions.
O In order for the bulb to
light, an electric
current must flow
between the two
electrodes that are
immersed in the
solution
O Sodium chloride, a
strong electrolyte, is
nearly 100%
dissociated into ions in
water.
O Glucose, a
nonelectrolyte, does
not dissociate in water.
O A nonelectrolyte is a
compound that does
not conduct an electric
current in either an
aqueous solution or
the molten state.
Electrolytes
O Not all electrolytes conduct electric current
to the same degree
O In a solution that contains a strong
electrolyte, all or nearly all of the solute
exists as ions. Ex: Sodium Chloride
O A weak electrolyte conducts an electric
current poorly because only a fraction of the
solute in the solution exists as ions.
O Ex: Acetic Acid
O Your cells use electrolytes,
such as sodium and
potassium ions, to carry
electrical impulses across
themselves and to other
cells
O An electrolyte imbalance
can occur if you become
dehydrated.
O When you exercise, you
can lose water and
electrolytes from your
body through perspiration.
O Pickles contain table
salt. Why can electric
current flow through a
pickle, causing it to
glow?
O Electrolytes conduct an
electric current when
they are in an aqueous
solution. Table salt, or
NaCl, is a strong
electrolyte. The water
and salt in the pickle
form a solution that
conducts an electric
current. The electric
current causes the
pickle to glow.
O Explain why you must
be extremely careful
when using
electricity near a
swimming pool.
O The chlorinated
water in a swimming
pool is a solution
that can conduct an
electric current. If a
current is introduced
into the water, any
swimmers could be
shocked.
O Why do
appliances warn
you not to use
them near water?
O Because there
are electrolytes in
tap water and
therefore it
conducts
electricity.
Thumbs Up…Thumbs Down
O All Solutions are conductors of electricity.
O Degree of electrical conductivity is directly
related to kinetic energy.
O Ionic compounds conduct electricity
because they contain ions.
Hydrates
O A compound that contains water of
hydration is called a hydrate.
O The dot is not a multiplication sign.
O It connects the compound to however many
water molecules are present.
Hydrates
The forces holding the water molecules in
hydrates are not very strong, so the water is
easily lost and regained.
O A piece of filter paper
that has been dipped in
an aqueous solution of
cobalt(II) chloride and
then dried is blue in color
(anhydrous CoCl2).
O When the paper is
exposed to moist air, it
turns pink because of the
formation of the hydrate
cobalt(II) chloride
hexahydrate
(CoCl2.6H2O).
Let’s test our knowledge…
O Pg. 510 #49
O Pg. 281 Chart 9.4
To determine what percent by
mass of a hydrate is water:
O First determine the mass of water in one
mole of hydrate.
O Then determine the molar mass of the
hydrate.
O The percent by mass of water can be
calculated using the following equation:
Finding the Percent by Mass of
Water in a Hydrate
O Pg. 500 #8
O Analyze -List the known and the unknown
O To determine the percent by mass, divide
the mass of water in one mole of the hydrate
by the molar mass of the hydrate and
multiply by 100%.
Let’s test our knowledge…
O Pg. 512 #89 d and e
OCalculate the percent by
mass of water in epsom
salt, magnesium sulfate
heptahydrate
(MgSO4.7H2O)
Test our Knowledge…
O What property of all ionic compounds make
them electrolytes?
O Why do hydrates easily lose water when
heated and regain water when exposed to
moisture?
O Identify the solvent and the solute in
vinegar, a dilute aqueous solution of acetic
acid.
Due Friday
O Online assignment calculating % by mass.