Saturated Solutions and Solubility
The opposite of the solution process (dissolution) is
There is an dynamic equilibrium between the solution
and solute + solvent; example: a liquid at its boiling
point is where the gas and liquid phases are in
solution is one where the solvent can
easily accept more solute, i.e., sugar in water.
A saturated solution is one where no more
solute can be dissolved in the solvent.
saturated solution for a given amount of solvent is
called the solubility of that solute in the solvent in
that experiment at that temperature.
solutions are also possible,
more solute is dissolved than normally would be
at equilibrium (think about supercooling).
Factors Affecting Solubility:
Polar liquids tend to dissolve in polar solvents;
non-polar liquids dissolve in non-polar solvents.
LIKE DISSOLVES LIKE!!!
Miscible liquids: mix in any proportions.
Ex.: water and alcohol;
water and ethylene glycol (antifreeze).
Immiscible liquids: do not mix at all.
Ex.: water and olive oil;
water and gasoline.
ethanol are miscible because the broken hydrogen
bonds in both pure liquids are re-established
(albeit in a different way) in the mixture (solution).
The number of carbon atoms in a chain can affect
the more C atoms in a compound, the less soluble
that compound is in water.
of -OH groups within a molecule increases
its solubility in water; sugars have many -OH groups,
and are very soluble in water.
(REMEMBER::::LIKE DISSOLVES LIKE!)
CALCULATE M OF 23.5 g NaOH DISSOLVED
IN ENOUGH WATER TO MAKE 450 mL OF SOLUTION.
CALCULATE m OF 23.5 g NaOH DISSOLVED
IN 450 mL OF WATER.
NOTICE THE DIFFERENCE BETWEEN THESE LAST TWO!!!
1 - CALCULATE M OF 25.5 g BENZENE (MW = 78.0 g/mol)
DISSOLVED IN ENOUGH CARBON TETRACHLORIDE
TO MAKE 550. mL OF SOLUTION.
M = 25.5g (1 mol/78.0g) / 0.550 L = 0.594 M
- CALCULATE m OF
25.5 g BENZENE (MW = 78.0 g/mol)
DISSOLVED IN 550. mL OF CARBON TETRACHLORIDE
(DENSITY OF CCl4 = 1.60 g/mL).
m = 25.5g (1 mol/78.0g)/550. mL(1.60 g/mL)(1kg/1000g)
m = 0.32602mol/ 0.880 kg = 0.370 m
Effect of Temperature on Solubility
For solids in liquids.....we note that sugar dissolves
more easily in warm water than in cold; the sugar is
more soluble in hot tea than in ice tea.
Therefore, as temperature increases, the solubility of
solids in solvents generally increases.
in liquids....experience tells us that
carbonated beverages go flat as they get warm.
Gases are less soluble at higher temperatures.
become less soluble and are not available for
plants or animals.
of Pressure on the Solubility
Solubility of a gas in a liquid is a function of the
pressure of the gas.
The higher the pressure of a gas ABOVE the solution,
the more molecules of gas are close to the surface
of the solvent and the greater the chance of a gas
molecule striking the surface and entering the
pressure of the gas, the
greater the solubility of the gas in the liquid.
the pressure of the gas ABOVE the solution,
fewer molecules of gas are close to the solvent,
and the lower the solubility.
Henry's law: kPgas = Cgas
is the partial pressure of gas above the
solution, in atm.
Cgas is the molar concentration of dissolved gas and
k = Henry's law constant for a particular gas and a
particular solvent at some T.
CO2 in water at
conditions if the solubility at 25oC and 1 atm is
0.034 mol/L. The partial pressure of CO2 in air is
0.00030 atm. kPgas = Cgas
Find k: k = C/P = 0.034 mol/L /1atm = 0.034 mol/L-atm
atmosphere: C = kP = 0.034mol/L-atm(0.00030atm)
C = 1.0 x 10-5 mol/L
As the bottle is opened, Pgas decreases and the
solubility of CO2 decreases. Therefore, bubbles of
CO2 escape from solution.
REACTS WITH WATER, HIGHER SOLUBILITIES RESULT.
EX: AMMONIA(g) + WATER GIVES THE AMMONIUM ION
AND HYDROXIDE ION. CARBON DIOXIDE REACTS
WITH WATER TO MAKE CARBONIC ACID.
Solutions (or collective properties)
depend on the quantity (numbers)
of individual solute particles (molecules OR ions):
Vapor Pressure Lowering:
SOLUTE = non-volatile: solutes reduce the ability
of the surface solvent molecules to escape the liquid.
Therefore, vapor pressure of solvent is lowered and
the amount of vapor pressure lowering depends on
the amount of solute. EX: sugar dissolved in water.
Raoult's Law: P1 = X1 P1o
is the vapor pressure of the solution, P1o
vapor pressure of the pure solvent, and X1 is the
mole fraction of the solvent in the solution.
NOTE: the decrease
in vapor pressure, DP, is directly
proportional to the concentration (mole fraction =X2)
of the solute present. LOWERING!!!
2) BOTH COMPONENTS ARE VOLATILE: THE VAPOR
PRESSURE OF THE SOLUTION IS THE SUM OF THE
INDIVIDUAL PARTIAL PRESSURES OF THE
PA AND PB ARE
PB=XB PBo PAo AND PBo ARE VAPOR PRESSURES
OF THE PURE SUBSTANCES.
PTOTAL= PA + PB
IS THE VAPOR PRESSURE OF
P1 + P2 + P3