The “
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SOLUBILITY
Solutions form between solute and solvent molecules can be predicted due to similarities between them. “Like dissolves Like,” refers to polar and nonpolar solvents and
solutes.
· Polar solids (this includes ionic solids) dissolve in water because the charged ions (polar) are attracted to the polar water molecules.
· Nonpolar molecules such as oil and grease dissolve in nonpolar solvents such as kerosene.
Factors Affecting Solubility
There are three main factors that control solubility of a solute.
(1) Temperature: Generally solubility increases with the rise in temperature and decreases with the fall of temperature but it is not necessary in all cases. However we must follow
two behaviors: In endothermic process solubility increases with the increase in temperature and vice versa. In exothermic process, solubility decrease with the increase in
temperature.
(2) Nature of solute or solvent: “Like dissolves Like”
(3) Pressure: The effect of pressure is observed only in the case of gases. An increase in pressure increases of solubility of a gas in a liquid. For example carbon dioxide is added
to cold carbonated drinks due to pressure.
Thus for gases, as the pressure of the gas above the solution increases, the solubility of the gas increases. For gases, as the temperature of the solution increases, the solubility of
the gas decreases. For most solids, as temperature increases, the solubility increases.
SOLUTIONS
A solution is a homogeneous mixture
of two substances: a solute and a
solvent.
-Solute:
substance
being
dissolved; present in lesser
amount.
-Solvent: substance doing the
dissolving; present in larger
amount.
-Solutes and solvents may be of
any phase of matter: solid,
liquid or gas.
FORMING SOLUTIONS
In order for a solution to form, the
solute intermolecular forces
(IMF’s) must be broken as well
as the solvent IMF’s. Then the
solute and solvent form new
intermolecular forces with each
other. If the energy required to
break the IMF’s is much greater
than the energy released when
the new IMF’s are formed, the
solution will not form and thus
the solute is insoluble.
COLLIGATIVE PROPERTIES
A colligative property is a property that depends on the number of solute particles in the sample.
The vapor pressure of a solution is lower than the pure solvent because the number of solvent
particles on the top layer that can evaporate is lower. Because the vapor pressure is lower, the
boiling point of a solution is always the higher than the pure solvent and the freezing point is
always lower than the pure solvent.
An electrolyte solution, one in which the solute breaks apart into multiple ions which allow electricity
to be conducted, has an even greater change in vapor pressure, boiling point or freezing point
because there are more particles in the solution than molecules added to the solution.
TYNDALL EFFECT
Colloids are mixtures with
solute particles large
enough
to
scatter
light. Colloids exhibit the
SOLUBILITY RULES
Tyndall Effect, where
Solubility is a physical property of a pure substance. Many observations over
light is seen traveling
time have led to some rules (generalizations) about the solubility of
through and spreading
certain salts. These rules are based on the terms soluble, insoluble, and
out in the colloid as it
slightly soluble. Using these rules, we can predict when a particular salt is
travels through it unlike a
likely to be soluble in water, and if we have an unidentified compound we
solution. The Tyndall
can design experiments to find out what it is.
Effect can be used as an
indicator to distinguish
Soluble:
Insoluble (0.10 M or greater):
• All Nitrates, Acetates, Ammonium, and • All Carbonates and Phosphates
between a solution and a
Group 1 (IA) salts
except Group 1 (IA) and
colloid
• All Chlorides, Bromides, and Iodides,
except Silver, Lead, and Mercury(I)
• All Fluorides except Group 2 (IIA),
Lead(II), and Iron(III)
• All Sulfates except Calcium, Strontium,
Barium, Mercury, Lead(II), and Silver
Ammonium
• All Hydroxides except Group 1
(IA), Strontium, Barium, and
Ammonium
• All Sulfides except Group 1 (IA), 2
(IIA), and Ammonium
• All Oxides except Group 1 (IA)
3 THINGS ABOUT ENERGY
Energy is the ability to do work which is using force to move an object a
distance.
1) Kinetic Energy (KE): Energy of MOTION; contained by anything that
MOVES. Atoms, molecules and other particles of that scale move faster
when temperature is increased.
2) Potential Energy (PE): STORED energy; energy that is not doing work
right now, but it has the ability to if released. Found in coiled springs,
chemical bonds, objects at a height above gravity, magnetism (both
attraction and repulsion)
Measurement: Since stored energy cannot be directly measured, it must be
converted to KE and measured using a CALORIMETER.
JOULE (J): The metric unit for PE. 1000 Joules is a kiloJoule (kJ), and is the
unit associated with PE changes in chemical and physical changes.
3) Heat Flow: Heat flows from where it is HOT to where it is NOT.
SOLUBILITY CURVES
A solubility curve shows the # of
grams of solute in a saturated
solution containing 100 mL or 100 g
of water at a certain temperature.
Any amount of solute below the line
indicates the solution is unsaturated
at a certain temperature
Any amount of solute above the line in
which all of the solute has dissolved
shows
the
solution
is
supersaturated.
If the amount of solute is above the
line, u, the solution is saturated and
the # grams of solute settled on
the bottom of the container = total
# g in solution – # g of a
saturated solution at that
temperature. (According to the
curve)
Solutes whose curves move upward
w/ increased temperature are
typically solids as the solubility of
solids increases w/ increased
temperature.
Solutes
whose
curves
move
downward
w/
increased
temperature are typically gases as
the solubility of gases decreases
with increased temperature.
Kinetic Molecular Theory AND THE PHASES OF MATTER
The “
Gas
assumes the shape and volume of its
container
particles can move freely past one
another
compressible
lots of free space between particles
Liquid
assumes the shape of the part of the
container which it occupies
particles can move/slide past one
another
not easily compressible
little free space between particles
flows easily
particles can move freely past one
another
separation between particles is very large
compared to their size no IMF’s (ideally)
between the molecules
flows easily
particles can move/slide past one
another
particles are farther apart than in a
solid
close enough that IMF’s confine the
material to the shape of its container
movement is somewhat constrained
due to weak IMF’s
liquid conforms to its container
movement of the particles is assumed to
be random and free due to lack of IMF’s
V for a quantity of gas is dependent on its
T and the surrounding P
”
Solid
retains a fixed volume and
shape
rigid - particles locked into
place
not easily compressible
little free space between
particles
does not flow easily
rigid - particles cannot
move/slide past one another
particles are close
IMF’s confine the material to
create the specific shape
motion of the particles is
severely constrained to a small
area
solid maintains its rigid shape
CALORIMETRY
Objects “warm-up: or “cool-down” by either gaining
energy or losing energy. In general, the more
massive the object, the greater the amount of
energy needed to raise its temperature. Likewise,
the energy given off when cooling off is greater
for a more massive object.
Note the distinction between heat capacity and
specific heat; specific heat is a property of a
substance and is phase dependent (it is not
affected by the size of the sample only by the
IMF interactions), while heat capacity is a
property of a particular object and phase
independent (a large, massive object can have
a large heat capacity even if it is made out of a
substance having a low specific heat).
Remember Δ = Final – Initial so
ΔT = Tfinal - Tinital
Heat (in J or cal)
Specific heat = CP = mass (in g) • ΔT
So the units for specific heat are...
Cp = J __
g • ˚C
Energy (heat) of TEMPERATURE changes: is all
about one formula.
∆T is the temperature
change experienced by the
substance as it warms or
cools in ⁰C
Note: ΔT = Tfinal - Tinital
CP is the specific heat
capacity of the substance
in J/(g•⁰C) and is phase
dependent.
q = m CP ΔT
Sublimation (solid → gas)
Deposition (gas → solid) =
Again phase transitions can
result from changing pressure
alone, temperature alone, or a
combination.
HEAT vs. TEMPERATURE
Heat is defined as the total KE of particles in a substance in
comparison to temperature being the average KE of
particles.
In a substance, heat reflects the particles average KE AND
the number of particles (mass).
In a substance, temperature reflects only the particles
average KE, not the total energy content.
PHASE DIAGRAMS
Shows the complete picture of the three phases of matter in
terms of conditions of temperature and pressure. i.e.
TEMPERATURE
Phase is Temperature and Pressure DEPENDENT.
Temperature is a measurement from something to noting (0 K)
The solid curve meets the liquid and gas curve at a triple
of movement at the atomic level.
point where all three phases are in equilibrium (important Kelvin’s zero point is absolute zero, the theoretical temperature
later). Every diagram has it limits. Every liquid has a
at which the molecules of a substance have the lowest
characteristic critical temperature, the highest point at
energy and thus cess moving. Many physical laws and
which the liquid phase can exist distinctly.
formulas can be expressed more simply when an absolute
Vaporization (liquid → gas)
Condensation (gas → liquid)
= Note that phase transitions
can result from changing
pressure
alone,
or
temperature alone, or a
combination.
Melting (solid → liquid) Freezing
(liquid → solid) = Again phase
transitions can result from
changing pressure alone, or
temperature alone, or a
combination.
temperature scale is used thus our use of Kelvin.
K = °C + 273.15
°C = K – 273.15
IMPORTANCE OF Δ
Δ means change in math/science. Change is defined as the
difference between final and initial conditions. Thus any
change may be calculated as:
Δ = final – initial
Note: By taking final-initial, the sing ( + or - ) of the change is
found, not just the numerical value of the change. This
removes the need to interpret if a change is + or -.
.
q is the total amount of thermal
energy absorbed or released by
a chemical system in joules (J)
m is the mass of
the substance in
grams (g)
Energy (heat) of PHASE changes: is all about one
formula.
q = m HFUS/VAP
NO ΔT as Temp is Hfus/vap is the Heat of Vaporization
not changing but ( l↔ g) or Heat of Fusion ( s ↔ l)
the phase
of the substance in J/g
HEAT AND COOLING CURVES
Best step by explanation found at:
http://lgfl.skoool.co.uk/viewdetails_KS3.a
spx?ID=593
3 P’s = Plateau
= Phase change
and Potential Energy Change.
Note: a Cooling Curve will remove Heat and go
from high temperature to low temperature as a
result