3/4/2010
Define solute and solvent.
Solute and Solvent 6a
Simple
solutions are homogenous mixtures of
two substances.
Solutions
Solute is the dissolved substance.
Solvent is the majority of the solution.
Chemistry Standard 6
Examples:
Dissolving 6b
Saltwater
Soda
salt = solute
water = solvent
sugar, coloring, CO2 = solutes
water = solvent
How do solutes dissolve in
solvents?
What is equilibrium?
Because
the molecules of a solvent and solute
are in constant random motion, they have
kinetic energy, the energy of motion.
This energy causes diffusion of the solute into
the solvent.
Once the solute molecules are evenly spread
throughout the solvent, they are said to be at
equilibrium.
4
Describe the process by
which salts dissolve in
water.
Not
all molecules dissolve equally in a solvent.
The
amount that dissolves is called the
equilibrium concentration.
When
salts dissolve in water, the anions and
cations are separated and surrounded by polar
water molecules.
These
form “hydration spheres”
It
depends on how attractive solute and
solvent are themselves and each other.
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3/4/2010
Factors Affecting Dissolution
6c
In
a liquid solvent, the solubility of gases and
solids is dependent on temperature.
Solids
are usually more soluble as you increase
temperature
Example: Sugar in iced tea vs. Sugar in hot tea
Gases
are less soluble as you increase
temperature
Example: warm water contains less oxygen and
can actually kill marine life.
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How are the solubilities of
solids and gases affected by:
- temperature?
- pressure?
Solubility
is also affected by pressure
The solubility of a gas in a liquid is “directly
proportional” to the pressure of that gas
above the solution.
In other words, if you increase the pressure of a
gas above a solution, you increase its solubility.
Example: When a soda can is pressurized, the CO2
is dissolved in the soda. Open the can and release
the pressure and the CO2 bubbles out since it’s
suddenly less soluble.
Units of Concentration
6d
The
concentration of a solution can be
measured several ways.
Grams per liter (g/L) represents the mass of
solute divided by the volume of the solution.
Molarity (M) (or mol/L) indicates the number of
moles of solute per liter of solution.
Percent composition (%) is the ratio of one part
solute to one hundred parts solvent.
To find -
mass _ solute
x100 = %composition
total _ mass
Parts per million (ppm) indicates the number of
molecules of solute for every million molecules of
solution.
To find - mass _ solute
x1,000,000 = parts _ per _ million
total _ mass
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