SOLUTION TERMINOLOGY 1.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: solutethe solute : the minor component (least number of moles) solventthe solvent : 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.

GENERAL PROPERTIES OF SOLUTIONS 1. 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 H 2 0 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 NH 3 + H 2 O  NH 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.

PROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONS 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 SOLUTIONS SOLUBILITY - describes the amount of solute that will dissolve in a solvent. Solubility is also used in a relative way for example, a substance can be considered either very soluble, moderately soluble, slightly soluble or insoluble of sodium chloride will dissolve in 100g of water at 20 o C, so the solubility of NaCl in water is 35.7 g/100g H 2 0 at 20 o C - 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, C 5 H 12, a nonpolar substance, is slightly soluble in water but very soluble in benzene and ether.

PROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONS Factors which effect solubility : 1. The size of the ions interacting 2. The charge of the ions interacting 3. Attractive and repulsive force interactions between ions 4. Intermolecular force interactions between solute and solvent. 5. Temperature 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 Solubility Rules for aqueous solutions Disclaimer: these rules do not address slightly soluble salts. 1. All Na +, K +, and NH 4 + salts are soluble. 2. All NO 3 - and most C 2 H 3 O 2 - are soluble. 3. The Halides are soluble except Ag +, Hg 2 2+, & Pb Sulfates are soluble except Ba 2+, Sr 2+, and Pb CO 3 2-, PO 4 3-, OH -, & S 2- 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 Solution A 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 DISSOLVING 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.

CuCl 2(s) H2O Cu +2 (aq) + 2 Cl – (aq)

PROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONS SATURATED A SATURATED 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

PROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONSPROPERTIES OF SOLUTIONS SUPERSATURATED In a SUPERSATURATED 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. supersaturated 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 20 o C but at 50 o C you would be able to dissolve 260 g. If the 50 o C saturated solution was allowed to cool to 20 o C and if the sugar remained in solution then the solution is said to be supersaturated. 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 20 o C saturation equilibrium is established.

PRACTICE PROBLEMS Short 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) CaF 2 d) (NH 4 ) 2 S 3. A saturated solution of sodium nitrate contains 80 g NaNO 3 per 100 g H 2 O. How many grams of NaNO 3 must be added to a solution containing 27 g NaNO 3 in 65 g H 2 O to make the solution saturated? a) 60 gb) 35 gc) 25 gd) 15 g B D

Short essayanswers: 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 0 o C is 0.12 g per 100 g of H 2 O therfore if you calculate the moles of solute: 0.12 g LiF (1 mol / g) = 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 PROBLEMS Short 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, Pb 2+ ? a) Br - b) SO 4 2- c) CO 3 2- d) NO 3 - e) PO 4 3- ___ 4. A saturated solution of potassium chloride contains 27.6 g KCl per 100 g H 2 O. How many grams of KCl must be added to a solution containing 50.0 g KCl in 235 g H 2 O to make the solution saturated?