Solutions are HOMOGENEOUS mixtures and can be gases
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UNIT 4 Solutions and Solubility Chapter 8 Solutions and Concentration Types of Solutions The simplest solutions contain 2 substances: 1. SOLVENT o any substance that has another substance dissolved in it. o The substance present in the largest amount (by volume, mass, or moles) 2. SOLUTE o The substance dissolved in the solvent. When solute dissolves in a solvent, it is a physical interaction and the substances can be separated by physical means (melting or boiling points). Solutions are HOMOGENEOUS mixtures and can be gases, liquids, or solids. Steel Carbon + Iron Koolaid Sugar + Water Air Nitrogen + Oxygen + Carbon Dioxide Most common solutions are liquid The most common of these are AQUEOUS SOLUTIONS where WATER is the SOLVENT. Many substances dissolve easily in any proportion. These substances are said to be MISCIBLE with each other. Ex. Water and Ethanol
Solutions are HOMOGENEOUS mixtures and can be gases
UntitledUNIT 4 Solutions and Solubility
Chapter 8 Solutions and Concentration
Types of Solutions
The simplest solutions contain 2 substances:
1. SOLVENT o
any substance that has another substance
dissolved in it. o
The substance present in the largest
amount (by volume, mass, or moles) 2.
SOLUTE o
The substance dissolved in the solvent.
When solute dissolves in a solvent, it is a physical
interaction and the substances can be separated
by physical means (melting or boiling points).
Solutions are HOMOGENEOUS mixtures
and can be gases, liquids, or solids.
Steel Carbon + Iron
Koolaid Sugar + Water
Air Nitrogen + Oxygen + Carbon Dioxide
Most common solutions are liquid
The most common of these are AQUEOUS
SOLUTIONS where WATER is the
SOLVENT.
Many substances dissolve easily in any
proportion. These substances are said to be
MISCIBLE with each other.
Ex. Water and Ethanol
Some substances do not dissolve in each other.
These are said to be IMMISCIBLE. Ex. Water
and Oil
SOLUBILITY is a measurement of the amount
of solute that dissolves in a given amount of
solvent, at a certain temperature. Ex. The
solubility of NaCl in H2O at 20oC is 36g per
100mL.
A SATURATED SOLUTION is a solution that
can not dissolve any more solute. If we try to
add more than 36g of NaCl to 100mL of H2O, it
will not dissolve.
If you try to add 40 g ...
An UNSATURATED SOLUTION is a solution that
has less than the maximum amount of solute
dissolved in the solvent.
Solutes described as SOLUBLE have a
solubility of greater than 1g/100mL
Solutes described as INSOLUBLE have a
solubility of less than 0.1g/100mL
Solutes described as SPARINGLY or
SLIGHTLY SOLUBLE have a solubility of
between 0.1g 1g / 100mL
Factors Affecting Rate of Dissolving
The RATE OF DISSOLVING measures
how fast a solute dissolves. This rate is
dependent on many factors.
1. TEMPERATURE a.
Solid solutes dissolve faster at
Temp. b.
temp means kinetic energy,
collisions between molecules of
solute and solvent.
2. Agitation a. Stirring or shaking increases
the rate of dissolving b.
Helps bring undissolved solute
in contact with solvent
3. Surface Area a.
surface area, rate of
dissolving.
b. surface area, # of
collisions between solute and
solvent.
The reason that one substance dissolves in another
is because of THE FORCES OF ATTRACTION
BETWEEN SOLVENT AND SOLUTE PARTICLES.
The intermolecular forces include the attraction
between: 1. SOLUTE and SOLUTE particles 2.
SOLVENT and SOLVENT particles 3.
SOLUTE and SOLVENT particles
When the force of attraction between
DIFFERENT particles is GREATER
THAN the attraction between LIKE
particles a solution is formed.
The STRENGTH of attraction between
particles determines solubility
Recall the Thought Lab on pg. 288:
Iodine was insoluble in water. This means that
the attraction between the nonpolar iodine and
the polar water was weak. Also the force of
attraction between water and water
(intermolecular forces) are strong.
Iodine was soluble in kerosene. The force of
attraction between nonpolar iodine and non
polar kerosene is stronger than the attraction
between iodine and iodine as well as
between kerosene and kerosene.
INTERMOLECULAR FORCES
In Unit 1 you learned the difference between
polar and nonpolar molecules.
Recall water:
Water is polar because it appears to
other molecules to have 2 oppositely
charge ends or “poles”. Molecules
like this are said to have a permanent
DIPOLE.
A DIPOLE consists of 2 opposite charges separated
by a short distance.
Remember how water “sticks” to water?
This is a result of the interactions between opposite
charges on different polar molecules. These are
called DIPOLEDIPOLE ATTRACTIONS.
This is a type of INTERMOLECULAR FORCE.
They act between molecules. These forces are
about 1% as strong as an ionic or covalent bond
(Intramolecular Force)
A special type of dipoledipole attraction
happens when hydrogen is chemically bonded
to O, N, or F. Because these atoms are so
electronegative, H gets a positive charge that
is extra strong. This leads to HYDROGEN
BONDING.
When IONIC substances are dissolved in a
polar solvent the cation and anions of the
ionic compound are attracted to different
ends of the polar compound. This is known
as IONDIPOLE ATTRACTION.
In an aqueous solution each cation and
anion will be surrounded by water
molecules. Each ion is said to be
HYDRATED and hydrated ions can move
freely in the solution making it an
ELECTROLYTE (soln with the ability to
conduct electricity).
Most ionic compounds are soluble but NOT ALL.
To predict solubility compare electronegativity:
Large difference Polar/Ionic Bonds Should
dissolve
Small difference Covalent Bond Should be
insoluble
When covalent compounds are mixed
with water, most are insoluble. This
is because many are nonpolar.
Exceptions are alcohols and sugars.
Both of these form Hbonds with
water.
However, nonpolar covalent
compounds are soluble in nonpolar
solvents.
In general LIKE dissolve LIKE.
Ionic and polar covalent solutes dissolve
in polar solvents.
Nonpolar solutes dissolve in nonpolar
solvents.
Some substances behave as both polar and non
polar substances. Acetic acid, small alcohols, and
soap are examples
Factors Affecting Solubility
(Don’t these get confused with rate of dissolving)
1. Molecule Size
Small molecules are more soluble than large.
Think of different alcohols
2. Temperature Solubility varies with temperature
When a solid dissolves energy is required to
break bonds between particles.
At increased Temp, more energy
available,solubility increases.
This is true for solids.
For liquids energy is not required so temp has
little effect on solubility.
When gases dissolve in liquids they actually
lose energy, so Temp adds
energy back and solubility.
3. Pressure
Changes in pressure have little/no
effect on solid and liquid solubility
The solubility of a gas is directly
proportional to the pressure of the
gas above the liquid.
For example in a 2L pop bottle the
pressure of CO2 is high (400 kPa).
Solubility of CO2 in the liquid is
high. When you open the bottle, the
pressure of CO2 above the liquid
drops to 0.03 kPa, solubility ↓ and
CO2 gas comes out of solution!
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