1. Solubility Experiment 1: Add 1 drop of red food coloring A B A B
Before
AFTER
Miscible – “mixable”
two gases or two liquids
that mix evenly
Water
COLD
Water
HOT
Water
COLD
Water
HOT
You should observe that temperature effects the rate of solution. As the temperature of the liquid solvent increases, the molecules move faster, and the food coloring dissolves more quickly.
A B
A B

2. Solubility Experiment 2: Add oil to water and shake T0 sec T30 sec
AFTER
Before
Immiscible – “does not mix”
two liquids or two gases
that DO NOT MIX
Oil
You should observe that for solutions to mix they must be chemically similar. Polar and polar molecules will mix, non-polar and non-polar molecules will mix, but polar and non-polar molecules will not mix. The reasons for this will be explained later.
Remember, ‘like dissolves like’. polar dissolves polar
non-polar dissolves non-polar
Water
Water
T0 sec
T30 sec

3. SUPERSATURATED SOLUTION
Solubility
UNSATURATED SOLUTION
more solute dissolves
SATURATED SOLUTION
no more solute dissolves
SUPERSATURATED SOLUTION
becomes unstable, crystals form
Maximum amount of a solute that can dissolve in a solvent at a specified temperature and pressure is its solubility.
– Solubility is expressed as the mass of solute per volume (g/L) or mass of solute per mass of solvent (g/g) or as the moles of solute per volume (mol/L).
– Solubility of a substance depends on energetic factors and on the temperature and, for gases, the pressure.
• A solution that contains the maximum possible amount of solute is saturated.
• If a solution contains less than the maximum amount of solute, it is unsaturated.
When a solution is saturated and excess solute is present, the rate of dissolution is equal to the rate of crystallization.
• Solubility increases with increasing temperature — a saturated solution that was prepared at a higher temperature contains more dissolved solute than it would contain at a lower temperature, when the solution is cooled, it can become supersaturated.
increasing concentration

4. Solubility Solids are more soluble at... Gases are more soluble at...
high temperatures.
Gases are more soluble at...
low temperatures &
high pressures (Henry’s Law).
EX: nitrogen narcosis, the “bends,” soda
External pressure has very little effect on the solubility of liquids and solids, but the solubility of gases increases as the partial pressure of the gas above a solution increases.
The concentration of molecules in the gas phase increases with increasing pressure, and the concentration of dissolved gas molecules in the solution at equilibrium is also higher at higher pressures.
Relationship between pressure and the solubility of a gas is described quantitatively by Henry’s Law: C = kP, where C is the concentration of dissolved gas at equilibrium; P is the partial pressure of the gas; and k is the Henry’s law constant, which must be determined experimentally for each combination of gas, solvent, and temperature and has units of mol/(L•atm) = M/atm.
Concentration of a dissolved gas in water at a given pressure depends strongly on its physical properties.
For a series of related substances, London dispersion forces increase as molecular mass increases with the Henry’s law constants increasing smoothly.
Gases that react chemically with water do not obey Henry’s law; all of these gases are much more soluble than predicted by Henry’s law

5. Solids dissolved in liquids Gases dissolved in liquidsTo
Sol. To
Sol.
As To , solubility
As To , solubility

6. Solubility vs. Temperature
200
180
160
140
120
100 80 60 40 20 KI
KNO3
Solubility (g solute / 100 g H2O)
NaNO3
The general rule of thumb is that solubility of solids increases with increases in temperature.
Maximum amount of a solute that can dissolve in a solvent at a specified temperature and pressure is its solubility.
– Solubility is expressed as the mass of solute per volume (g/L) or mass of solute per mass of solvent (g/g) or as the moles of solute per volume (mol/L).
– Solubility of a substance depends on energetic factors and on the temperature and, for gases, the pressure.
• A solution that contains the maximum possible amount of solute is saturated.
• If a solution contains less than the maximum amount of solute, it is unsaturated.
When a solution is saturated and excess solute is present, the rate of dissolution is equal to the rate of crystallization.
• Solubility increases with increasing temperature — a saturated solution that was prepared at a higher temperature contains more dissolved solute than it would contain at a lower temperature, when the solution is cooled, it can become supersaturated.
Solubility of a substance generally increases with increasing temperature
No relationship between the structure of a substance and the temperature dependence of its solubility
Solubility may increase or decrease with temperature; the magnitude of this temperature dependence varies widely among compounds
This variation of solubility with temperature is used to separate the components of a mixture by fractional crystallization, the separation of compounds based on their solubilities in a given solvent
Fractional crystallization is a common technique for purifying compounds; the compound of interest must be more soluble at high temperature than at low temperature, so that lowering the temperature causes it to crystallize out of solution
Solubility of gases in liquids decreases with increasing temperature
Attractive intermolecular interactions in the gas phase are essentially zero for most substances
When a gas dissolves, its molecules interact with solvent molecules and heat is released when these new attractive interactions form, therefore, dissolving most gases in liquids is an exothermic process (Hsoln < 0)
Adding heat to the solution provides thermal energy that overcomes the attractive forces between the gas and the solvent molecules, thereby decreasing the solubility of the gas
Na3PO4
NaCl 20 40 60 80
100
Temperature (oC)
Timberlake, Chemistry 7th Edition, page 297

7. Gas Solubility Higher Temperature …Gas is LESS Soluble CH4 O2
2.0 O2
Higher Temperature
…Gas is LESS Soluble CO
Solubility (mM)
1.0
The general rule of thumb is that the solubility of gases decreases when temperature increases.
Solubility of a substance generally increases with increasing temperature
No relationship between the structure of a substance and the temperature dependence of its solubility
Solubility may increase or decrease with temperature; the magnitude of this temperature dependence varies widely among compounds
This variation of solubility with temperature is used to separate the components of a mixture by fractional crystallization, the separation of compounds based on their solubilities in a given solvent
Fractional crystallization is a common technique for purifying compounds; the compound of interest must be more soluble at high temperature than at low temperature, so that lowering the temperature causes it to crystallize out of solution
Solubility of gases in liquids decreases with increasing temperature
Attractive intermolecular interactions in the gas phase are essentially zero for most substances
When a gas dissolves, its molecules interact with solvent molecules and heat is released when these new attractive interactions form, therefore, dissolving most gases in liquids is an exothermic process (Hsoln < 0)
Adding heat to the solution provides thermal energy that overcomes the attractive forces between the gas and the solvent molecules, thereby decreasing the solubility of the gas He 10 20 30 40 50
Temperature (oC)

8. Pure water does not conduct an electric current
Source of
electric power
Pure
water
Pure water doesn’t conduct electricity because it contains no ions. Ions (cations have (+) charges) carry electrons in solution. The flow of electrons is called electricity.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 215

9. Ionic Solutions conduct a Current
Source of
electric power
Free ions
present
in water
To make a solution that conducts electricity (an electrolyte) – an ionic salt is added. An alternative method is to add acid. In truth, most acids are oxysalts dissolved in water.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 215

10. Electrolytes
Classify each compound as either a strong electrolyte or a nonelectrolyte.
If a compound is a nonelectrolyte, the concentration is the same as the molarity of the solution.
If a compound is a strong electrolyte, determine the number of each ion contained in one formula unit and find the concentration of each species by multiplying the number of each ion by the molarity of the solution.
(a) Nonelectrolyte (b) Weak electrolyte (c) Strong electrolyte
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

11. Electrolytes Electrolytes - solutions that carry an electric current
Electrolyte — any compound that can form ions when it dissolves in water
– When strong electrolytes dissolve, constituent ions dissociate completely, producing aqueous solutions that conduct electricity very well.
– When weak electrolytes dissolve, they produce relatively few ions in solution, and aqueous solutions, of weak electrolytes do not conduct electricity as well as solutions of strong electrolytes.
– Nonelectrolytes dissolve in water as neutral molecules and have no effect on conductivity.
strong electrolyte
weak electrolyte
nonelectrolyte
NaCl(aq) Na+ + Cl-
HF(aq) H+ + F-
Timberlake, Chemistry 7th Edition, page 290

12. Solution, Suspension, Colloid
The main difference between a solution, colloid and suspension is in PARTICLE SIZE. With a solution, the particles are very small (too small to be seen with the naked eye) and are dissolved between the molecules of the solvent (in the interstitial spaces). With a colloid, the particles are still small enough to fit in the interstitial spaces, but are large enough to be seen with the naked eye. Both a solution and a colloid are homogeneous mixtures. In a colloid, the particles are not dissolved in the solution, they are too large to fit in the interstitial spaces. Instead, they are stirred up and suspended in the solvent for short periods of time. Suspensions settle out when allowed to stand undisturbed.
Two common types of mixtures whose properties are intermediate between those of true solutions and heterogeneous mixtures are:
1. Suspension — a heterogeneous mixture of particles with diameters of about 1 m (1000 nm) that are distributed throughout a second phase, if allowed to stand, the two phases will separate
2. Colloid — a heterogeneous mixture with particles smaller than those of a suspension (2 – 500 nm in diameter) that do not separate into two phases on standing
Mixture of gases is the only combination of substances that cannot produce a suspension or colloid because their particles are small and form true solutions
Graham characterized colloids in 1860 and found that they diffuse very slowly or not at all.
• A colloid can be classified as
1. a sol or gel, a dispersion of solid particles in a liquid or solid in which all the solvent has been absorbed by the solid particles, thus preventing the mixture from flowing readily;
2. An aerosol, a dispersion of solid or liquid particles in a gas;
3. An emulsion, a dispersion of one liquid phase in another liquid with which it is immiscible.
• Colloids share many properties with solutions — the particles in both are invisible without a microscope, do not settle on standing, and pass through most filters.
• A colloid can be distinguished from a true solution by its ability to scatter a beam of light, known as the Tyndall effect.
Colloids and suspensions can have particles similar in size, but the two differ in stability.
– The particles of a colloid remain dispersed indefinitely unless the temperature or chemical composition of the dispersing medium is changed.
– Chemical explanation for the stability of colloids depends on whether the colloidal particles are hydrophilic or hydrophobic.
– Hydrophilic colloids contain an outer shell of groups that interact favorably with water, whereas hydrophobic colloids have an outer surface with little affinity for water.
– A stable colloid can be transformed to an aggregated suspension by a minor chemical modification.
– Aggregation and precipitation can result when the outer, charged layer of a particle is neutralized by ions with the opposite charge.
Emulsions are colloids formed by the dispersion of a hydrophobic liquid in water, thereby bringing two mutually insoluble liquids in close contact.
• Various agents have been developed to stabilize emulsions, the most successful being molecules that combine a relatively long hydrophobic “tail” with a hydrophilic “head.”
• Examples of emulsifying agents include soaps and detergents.
Timberlake, Chemistry 7th Edition, page 309

13. Tyndall Effect Put a beam of light through a mixture
Reflection of light off undissolved particles
A) Solution - no Tyndall effect- can’t see the beam
B) Suspensions - sparkle off big particles
C) Colloids – continuous beam A B C

14. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.