SSOOLLUUTTIIOONN TERMINOLOGY TERMINOLOGY1. A solution is a homogeneous mixture that can exist in

any of the three states – gas liquid or solid.• Air is a gaseous solution • Metal alloys are solid state solutions• Carbonated beverages are liquid solutions of a gas

2. A solution is composed of:• the solutesolute: the minor component (least number of moles)• the solventsolvent: the major component (largest number of moles)

3. Concentrated / Dilute: A concentrated solution has a relatively large quantity of a specific solute per unit amount of solution. A dilute solution has a relatively small quantity of a specific solute per unit amount of solution.

GGEENNEERRAAL PL PRROOPPEERRTTIIEESS O OFF S SOOLLUUTTIIOONNSS1. A solution is a homogeneous mixture of two or

more components.

2. It has variable composition.

3. The dissolved solute is molecular or ionic in size.

4. A solution may be either colored or colorless nut is generally transparent.

5. The solute remains uniformly distributed throughout the solution and will not settle out through time.

6. The solute can be separated from the solvent by physical methods.

ELECTROLYTES REVIEW

Electrolytes are substances which will conduct electricity when dissolved in water.

Salts and Strong Acids & Bases form Strong Electrolyte H20

HCl(s) H+ + Cl-

Salt and strong acids (and bases) are fully dissociated therefore all of the ions present are available to conduct electricity.

Weak Acids and Weak Bases form Weak Electrolytes

NH3 + H2O NH4+ + OH

Weak electrolytes are partially dissociated therefore not all species in solution are ions, some of the molecular form is present. Weak electrolytes have less ions available to conduct electricity.

PPRROOPPEERRTTIIEESS O OFF S SOOLLUUTTIIOONNSS

1. Soluble / Insoluble: A soluble substance readily dissolves in the solvent. An insoluble substance will NOT dissolve readily in a solvent.

2. Miscible / Immiscible: Two liquids are miscible in each other if they readily mix to form a uniform solution. Two immiscible liquids will always separate out into two distinct layers.

PROPERTIES OF SOLUTIONSSOLUBILITYSOLUBILITY - describes the amount of solute that will dissolve in a - describes the amount of solute that will dissolve in a

solvent. Solubility is also used in a relative way for example, a solvent. Solubility is also used in a relative way for example, a substance can be considered either very soluble, moderately substance can be considered either very soluble, moderately soluble, slightly soluble or insoluble.soluble, slightly soluble or insoluble.- 35.7 of sodium chloride will dissolve in 100g of water at 20oC, so the solubility of NaCl in water is 35.7 g/100g H20 at 20oC- Polar or ionic substances tend to be more miscible with other polar substances.- Nonpolar substances tend to be miscible with other nonpolar substances.

For example:1) Sodium Chloride (ionic substance) is soluble in water, slightly

soluble in ethyl alcohol and insoluble in ether and benzene.2) Pentane, C5H12, a nonpolar substance, is slightly soluble in water

but very soluble in benzene and ether.

PPRROOPPEERRTTIIEESS O OFF S SOOLLUUTTIIOONNSSFactors which effectFactors which effect solubilitysolubility::

1. The size of the ions interacting1. The size of the ions interacting

2. The charge of the ions interacting2. The charge of the ions interacting

3. Attractive and repulsive force interactions 3. Attractive and repulsive force interactions between ionsbetween ions

4. Intermolecular force interactions between 4. Intermolecular force interactions between solute and solvent.solute and solvent.

5. Temperature5. Temperature

6. Pressure (for gas/liquid solutions)6. Pressure (for gas/liquid solutions)

Factors that Determine Solubility

Intermolecular Forces: “Like dissolves like”

Factors that Determine Solubility Temperature: Solubility of most solids

increases with rising temperature. The solubility of gases in liquids are generally lower at higher temperatures.

Factors that Determine Solubility

Partial Pressure of a Solute Gas over Liquid Solution: “Soda Pop”

General General Solubility Solubility Rules for aqueous Rules for aqueous solutionssolutions

Disclaimer: these rules do not address slightly soluble salts.

1. All Na+, K+, and NH4+ salts are soluble.

2. All NO3- and most C2H3O2

- are soluble.

3. The Halides are soluble except Ag+, Hg22+, & Pb2+.

4. Sulfates are soluble except Ba2+, Sr2+, and Pb2+.

5. CO32-, PO4

3-, OH-, & S2- are insoluble except for those mentioned in #1.

Formation of a Solution

• The dissolving process is reversible. As the dissolved solute particles move randomly through the solution, the come into contact with the un-dissolved solute and crystallize (return to the solid state).

• The rate per unit of surface area at which a solute dissolves depends primarily on temperature.

• The rate of crystallization per unit area depends primarily on the concentration of the solute at the crystal surface.

Formation of a Solution

When the rates of dissolving and crystallization become the same, the solution is saturated at its solubility at that temperature and dynamic equilibrium is reached. When equilibrium is reached, the solution is saturated.

Formation of a SolutionA soluble ionic crystal is placed in water, the negatively charged ions at the crystals surface are attracted by the positive region of the polar water molecule. A “tug of war” begins between the crystal and the water resulting in a hydrated crystal.

FACTORS EFFECTING THE RATE OF FACTORS EFFECTING THE RATE OF DISSOLVING SOLIDSDISSOLVING SOLIDS

1. Particle size: The smaller the particle size, the more surface area that is exposed thus the easier the solute dissolves.

2. Temperature: In many cases, temperature increases the rate of dissolving.

3. Concentration of solution: Dissolving is easier when there is less solute particles. The rate of dissolving decreases as the solution nears saturation.

4. Agitation: Stirring and swirling a solution increases the kinetic motion thus increases dissolving.

CuCl2(s) H2O Cu+2(aq) + 2 Cl–

(aq)

PPRROOPPEERRTTIIEESS O OFF S SOOLLUUTTIIOONNSSA SATURATEDSATURATED solution occurs when the rate of dissolving of the solute (pink dots) into the solvent (blue dots) is in equilibrium with the rate of formation of the solute back into crystalline form. No more solute can be added without disturbing the equilibrium, resulting in the solute “falling” out of solution and crystal reformation is apparent. In this picture since the salt crystal is visible, the solution “saturated” with the solute. This solution has the maximum amount of solute dissolved.

A salt crystal in water

PPRROOPPEERRTTIIEESS O OFF S SOOLLUUTTIIOONNSS In a SUPERSATURATEDSUPERSATURATED solution, the amount of

solute dissolved in the solvent is beyond the saturated amount. This is possible by altering some physical conditions in order to “shift” the equilibrium so more solute can dissolve.

For some substances, an increase in the temperature is one way to increase how much solute will dissolve in a given solvent. 204 g of sugar will dissolve in 100 g of water at 20oC but at 50oC you would be able to dissolve 260 g. If the 50oC saturated solution was allowed to cool to 20oC and if the sugar remained in solution then the solution is said to be supersaturatedsupersaturated. This is usually an unstable situation and any disturbance to the cooled solution could cause the excess solute to “fall out” of solution as the 20oC saturation equilibrium is established.

PRACTICE PROBLEMSShort essay: (answers on next slide)1. Can a saturated solution ever be a dilute solution? Explain.

2. According to the general solubility rules, which one of the following compounds would be insoluble?

a) NaBr b) CuS c) CaF2 d) (NH4)2S

3. A saturated solution of sodium nitrate contains 80 g NaNO3 per 100 g H2O. How many grams of NaNO3 must be added to a solution containing 27 g NaNO3 in 65 g H2O to make the solution saturated?

a) 60 g b) 35 g c) 25 g d) 15 g

BB

DD

Short essayanswers:1. Can a saturated solution ever be a dilute solution? Explain.1. Can a saturated solution ever be a dilute solution? Explain.

Yes, a saturated solution can be dilute since the two terms do not correspond to each other. A saturated solution has the dissolved solute in equilibrium with undissolved solute, that is, all possible solute is already dissolved for that given temperature. A dilute solution contains a small amount of solute relative to the solvent.

An example of a dilute solution that is saturated would be LiF in water, the solubility of LiF at 0oC is 0.12 g per 100 g of H2O therfore if you calculate the moles of solute:

0.12 g LiF (1 mol / 25.94 g) = 0.0046 mol of solute

The moles of solvent is: 100 g ( 1 mol / 18 g ) = 5.55 mol of solvent

Upon comparison, since the moles of solvent is 99.9% more than the moles of solute, one could argue that LiF is dilute relative to the solvent (Although still saturated).

GROUP STUDY PROBLEMSShort Essay (write answers on back)

1. Some drinks like tea are consumed either hot or cold but soft drinks are drunk only cold. Explain.

2. In a saturated solution containing undissolved solute, the solute is continuously dissolving, but the concentration of the solution remains unchanged. Explain.

___ 3. According to the general solubility rules, which of these salts will not form a precipitate with lead ion, Pb2+?

a) Br- b) SO42- c) CO3

2- d) NO3- e) PO4

3-

___ 4. A saturated solution of potassium chloride contains 27.6 g KCl per 100 g H2O. How many grams of KCl must be added to a solution containing 50.0 g KCl in 235 g H2O to make the solution saturated?